2011 Unnamed Tropical Storm

Storm Active: August 31-September 2

*This cyclone was classified as a tropical storm during the 2011 postseason analysis. It therefore received no name, despite being tabulated in the number of tropical depressions and tropical storms of the 2011 season.

On August 29, a circulation took shape in an area of convection north of Bermuda, some of which had been associated with Tropical Storm Jose a few days previously. The resulting trough organized over the next few days, increasing in shower activity. Late on August 31, a closed low formed on the southeastern edge of the shower activity, and the system became a tropical depression (although it was not then recognized as such). Convection increased markedly on September 1, and gale force winds were recorded, suggesting that the cyclone at this time became a tropical storm.

A banding feature to the southwest of the center formed the same day, and the cyclone strengthened overnight, reaching its peak intensity of 45 mph winds and a pressure of 1002 mb early on September 2. By this time, an approaching front had begun to push the system northeast, away from the U.S. east coast. The proximity of the front caused the unnamed storm to lose definition during the day of September 2, and the system became extratropical that evening. The remnants continued to move north-northeastward, and were fully absorbed on September 2. This event marked the first time since 2006 that a tropical storm was added in postseason analysis.



The unnamed tropical storm weakening on September 2.



Track of the unnamed tropical storm.

2011 Season Summary

The 2011 Atlantic hurricane season was an above average season, with

20 cyclones attaining tropical depression status
19 cyclones attaining tropical storm status*
7 cyclones attaining hurricane status†
and 3 cyclones attaining major hurricane status

*In the NHC postseason analysis, an additional unnamed tropical storm was identified to have formed during the month of September. This means, that although 2011 only reached the letter "S" in tropical cyclone names, and 2010 reached "T", both seasons had the same number of tropical cyclones form.

†Nate was upgraded from a tropical storm to a hurricane during the postseason analysis.

At the beginning of the season, I predicted that there would be

20 cyclones attaining tropical depression status
19 cyclones attaining tropical storm status
10 cyclones attaining hurricane status
and 6 cyclones attaining major hurricane status

The tropical depression and tropical storm predictions happened to be exactly correct, although there was a lower number of hurricanes and major hurricanes than I predicted. As with the 2010 season, the 2011 season was tied for third in overall number of tropical storms with 19. This was caused by an ongoing La Nina event that actually intensified towards the latter part of the season. However, many of these storms were short-lived, and this reflects the abundance of favorable conditions for formation, but not for intensification. These conditions included high wind shear over much of the Caribbean for long periods of time, and also large pockets of dry air associated with anticyclones, which worked their way into many developing systems.

Some notable cyclones and facts about the season include:

• Hurricane Ophelia, the strongest storm of the season, attained Category 4 status at an unusually high latitude of 32.5° N
• 2011 was the first season in which none of the first eight tropical storms (Arlene through Harvey) became a hurricane
• Hurricane Irene, the first hurricane and major hurricane of the season, was also the first cyclone of hurricane strength to make landfall in the U.S. since Ike of 2008
• An unnamed tropical storm formed in early September, the first cyclone to be recognized only in the postseason analysis since 2006
• Nate was upgraded from a tropical storm to a hurricane in postseason analysis, the first such instance since 2007
• Hurricane Philippe was the longest lived storm in the Atlantic basin since 2008, but, despite its longevity, it affected no land.

Overall, the 2011 season was one of numerous, but weak, storms. The U.S. was affected much more than it had been in the previous two years with one hurricane and two tropical storm landfalls, but the damage associated with these systems was not severe.

Tropical Storm Sean (2011)

Storm Active: November 8-11

On November 4, a frontal boundary moved off of the U.S. east coast. A low pressure system along the front deepened as it moved off the coast of North Carolina later that day. The section of the front to the north of the low had most of the cloud cover associated with it, but the convection moved closer to the circulation of November 6, as the system drifted southeast. After temporarily losing definition, the low strengthened again on November 7. By this time, gale force winds occupied a region around the low, extending hundreds of miles in each direction.

Over the following day, the southern extension of the frontal boundary degenerated, devolving into a banding feature expanding clockwise from the low. Meanwhile, the remainder of the front had moved away to the east, and the leftover moisture became entrenched in the circulation of the cyclone. Early on November 8, convection had circumnavigated the center, and the system was upgraded to Subtropical Storm Sean.

The cyclone continued to increase in organization that afternoon, the eye contracting, and the surface circulation becoming better defined. The movement of the circulation into the lower levels of the atmosphere merited a reclassification of Sean into a tropical storm. Throughout the day, Sean remained nearly stationary, initially revolving around a broader cyclonic center, and later adopting a slow westward motion. Convection developed in earnest during the morning of November 9, and the system intensified into a strong tropical storm, also forming an eye feature.

By this time, Sean had entered the steering currents of the west Atlantic and began to accelerate northward. On November 10, the system curved to the northeast, also reaching its peak intensity of 65 mph winds and a pressure of 983 mb. Late that night, the windfield of Sean enveloped Bermuda, causing tropical storm force winds on the island, along with periods of heavy rain.

As it moved away from Bermuda on November 11 winds shear drastically increase and extratropcal transition began as Sean cam into close proximity with a front. By that evening, the center had elongated, and convective bands associated with the circulation ere stripped away. As a result, the system became extratropical that night. Sean caused minor damage and one fatality in Bermuda.



Tropical Storm Sean near peak intensity on November 10. The Outer Banks of North Carolina are visible on the upper left.



Erratic track of Sean through the Western Atlantic.

Hurricane Rina (2011)

Storm Active: October 23-28

During the day of October 18, a cold front swept across the Gulf coast. Heading unusually far south, the front continued to moved over the Gulf, crossing the Yucatan Peninsula during the afternoon of October 19. Simultaneously, a tropical wave, moving through the Caribbean, degenerated into a trough, though it still produced showers and thunderstorms. On October 20, these systems merged off of the coast of Nicaragua and a low pressure system formed.

Over the next day, the low drifted south and then west, all the while increasing in organization. Thunderstorm activity became concentrated just off the coast of Nicaragua during the evening of October 21, However southwesterly wind shear displaced thunderstorm to the west of the low pressure center, causing some heavy rainfall in Central America the following day. On October 23, now moving northward off of the coast of Honduras, the low experienced a reformation, with the new center within the southern edge of the convection. That afternoon, sufficient organization had been attained to classify the system as Tropical Depression Eighteen.

An increase in the symmetry of Eighteen later that night merited an upgrade to Tropical Storm Rina. A series of increases in sturutal organization followed early on October 24, with the outflow imporving in all quadrants. Despite this, the eyewall itself did not undergo any major changes until the early afternoon, at which time a contraction caused a well-defined eyewall, as well as a radiating band feature, to form. Rina was therefore upgraded directly from 45 mph to a hurricane.

Shortly afterward, Rina turned to the west and decreased in speed due to the influence of a ridge over the Gulf of Mexico. Meanwhile, Rina's internal structure continued to improve, and an eye appeared on visible, but not infrared images. Therefore, early on October 25, the cyclone underwent another burst of strengthening and became a Category 2 hurricane. Further fluctuations in the strength of the eyewall pushed Rina to its peak intensity that night, achieving winds of 110 mph and a pressure of 966 mb.

The hurricane maintained this intensity through the morning, but a tongue of dry air invaded from the north. This, coupled with increasing wind shear caused rapid deteriorated of the circulation, reducing Rina's intensity to that of a Category 1 hurricane. As the cyclone began to turn north, the area of deep convection associated with the system shrunk. By October 27, interaction with the Yucatan Peninsula to the west and the exposure of the center of circulation weakened Rina to a tropical storm. Later that day, Rina made landfall near Cancun, causing heavy rainfall and a small area of tropical storm force winds.

By the morning of October 28, the system emerged into the Yucatan Channel and weakened into a tropical depression. All convection had been displaced to the north by this time, and Rina degenerated into a remnant low that afternoon. It was absorbed by a front the next day. Due to its rapid degeneration, the cyclone caused only minimal damage in Central America.



Hurricane Rina at peak intensity, with an eye feature apparent on visible imagery.



Track of Rina.

Hurricane Philippe (2011)

Storm Active: September 24-October 8

A well-defined low pressure area formed west of the African nation of Guinea on September 23. The low deepened rapidly later that day, already having developed large rain bands spread out evenly around the circulation. Convection decreased that night, but became very concentrated near the center, and the system became closed early the next morning. It was then declared Tropical Depression Seventeen. Slow organization followed later in the day as Seventeen moved west-northwest, and the system soon intensified into Tropical Storm Philippe.

A weakness in the ridge to Philippe's north allowed it to turn northwestward and decelerate into the day of September 25, when it reached an intensity of 60 mph winds and a pressure of 997 mb. The tropical storm maintained this strength into September 26, by which time it began to encounter higher wind shear and cooler waters. A gradual weakening ensued, as the circulation became exposed on September 27. That afternoon, Philippe's forward motion slowed to 5 mph and its shallow circulation was steered back to the west-northwest with a restrengthening of the subtropical ridge to its north.

That night, despite the fact that Philippe was a minimal tropical storm with little convection near the center, the outflow remained fairly robust, and thunderstorm activity reappeared just north of the center on September 28. The cyclone even strengthened a little that day. On September 29, the center reformed to the north of its previous position, and once again was completely enveloped in the convection associated with Philippe. The exact center position of Philippe remained difficult to identify overnight, but the circulation became more well-defined on September 30, and the cyclone strengthened further.

As the storm moved farther to the northwest, it encountered very strong shear associated with the outflow of Ophelia, but the tropical storm once again demonstrated resilience to strong upper-level winds, and maintained its intensity, deep convection even increasing near the center of circulation overnight. An analysis of the windfield of Philippe revealed it to be stronger than expected, with winds of 65 mph. Late that night, more intensification occurred, bringing Philippe to the verge of hurricane strength early on October 2.

However, the unfavorable conditions near the cyclone finally began to take their toll that morning, exposing the center and weakening the system. As before, however, Philippe recovered its convection, as Ophelia moved north, and conditions became less hostile. The next day, winds were found to be stronger than previously estimated, and the cyclone was a strong tropical storm yet again. Meanwhile, the center reformed farther to the south than before, and Philippe moved west-southwestward during the day of October 3.

After navigating around the periphery of the ridge steering it, the tropical storm began to turn north on October 4. Recurvature occurred quickly during the following days, and shear gradually decreased. On October 5, the center remained displaced from the deepest convection, but, on October 6, strengthening finally began, bringing Philippe to hurricane strength after over 12 days as a tropical cyclone. An eye feature formed later that evening, particularly visible on infrared imagery, and the hurricane reached its peak intensity of 90 mph winds and a pressure of 976 mb that evening.

Upper-atmospheric conditions rapidly deteriorated on October 7, causing weakening as the cyclone accelerated to the east-northeast. The center quickly became exposed that afternoon, and Philippe's brief period as a hurricane was over. A front encouraged extratropical transition on October 8, and absorbtion completed in that afternoon. Philippe was the longest lived tropical cyclone in the Atlantic since Bertha of 2008, lasting over two weeks. Despite this, it affected no land.



Hurricane Philippe over the open Atlantic.



Track of Philippe.

Hurricane Ophelia (2011)

Storm Active: September 20-October 3

On September 17, a broad area of showers and thunderstorms formed in association with a large low pressure system in the eastern Atlantic. Three low pressure centers existed in close proximity near the area during the day of September 18, oriented west to east near the 10ºN parallel. Over time, the central low became stronger and dissipated the others, and convection increased. The circulation also increased in definition over the following days, but numerous reformations of the center kept the circulation open. However, late on September 20, thunderstorms became concentrated near a single circulation center, and the low was upgraded directly to Tropical Storm Ophelia.

As the tropical storm moved west over the central Atlantic, shear steadily increased, but despite unfavorable conditions, winds in Ophelia's rain bands increased significantly, and strengthening ensued. On September 21, convection was displaced to the east of the center, but notwithstanding any satellite data to the contrary, winds were reported that suggested a strong tropical storm intensity. By the morning of September 22, Ophelia had reached an intensity of 65 mph winds and a pressure of 994 mb.

Wind shear began to finally take its toll on the system later that day, and the cyclone weakened. By the morning of September 23, Ophelia, had weakened to a minimal tropical storm, and all remaining convection was pushed northeast into a rain band that extended several hundred miles. Meanwhile, Ophelia took a turn to the west-northwest. Later on September 23, shear temporarily relaxed, and shower activity re-ignited near the center of the cyclone, causing it to unexpectedly strengthen that evening.

However, this increase in intensity did not persist, as strong upper-level winds resumed early on September 24. Ophelia weakened once again during that day, and, as a result, turned back to the west. As the system's circulation continued to become shallower, a due west motion was assumed, and by the morning of September 25, Ophelia was a minimal tropical storm. A large area of convection was over 150 miles east of the center during the day, with the center itself bare but for a few showers to the northeast. The Lesser Antilles, to Ophelia's southwest, experienced some gusty winds during the afternoon, as the center of the circulation became more elongated. Subsequently, the system was observed to lack tropical characteristics, and was downgraded to a remnant low.

The exposed center quickly dissipated, but a new swirl quickly became evident in the thunderstorm activity to the east. During the day of September 26, upper-level winds relaxed, and the circulation of the newly formed low became much better defined that evening. As the system continued to organize overnight, it drifted eastward and southward, stalling close to the Leeward Islands. On September 27, moderate rainfall occurred over these islands, as convection increased further during the afternoon, and the low became organized enough to be redesignated as Tropical Depression Ophelia.

Shear still abounded over the region overnight, and strengthening was gradual, bringing Ophelia to tropical storm strength during the morning of September 28. By this time, the cyclone had assumed a definite north-northwestward motion, and it moved away from the Caribbean. Outflow improved throughout the same day, allowing the cyclone to hold its own despite marginally favorable conditions. Further strengthening followed that night, and the system was a powerful tropical storm by September 29. An impressive banding feature formed to the east of the circulation later that afternoon, causing Ophelia to be upgraded to Category 1 hurricane status.

During the same evening, Ophelia's eyewall solidified, and the eye itself became more consistent in its appearance on satellite imagery. Following these structural changes, the cyclone rapidly strengthened. By the morning of September 30, Ophelia was a Category 2 hurricane! However, the strengthening was by no means over, as the hurricane assumed a more rounded appearance, the outflow improving and the eye broadening further. By that afternoon, Ophelia was a Category 3 hurricane. Meanwhile, the storm turned north and started to accelerate, as a large trough exited the U.S. east coast and pushed it farther poleward. Late that night, the system finally stabilized in intensity at 120 mph winds and a pressure of 956 mb.

Early on October 1, the pressure dropped slightly to 952 mb, and the outer bands of Ophelia began to impact Bermuda. During the day, gusty winds and scattered heavy squalls affected the island, but the hurricane passed well to the east, making its closest approach late that afternoon. Just after passing Bermuda, Ophelia unexpectedly underwent rapid intensification, bringing it to its peak intensity as a Category 4 hurricane with 140 mph winds and a pressure of 940 mb. During the morning of October 2, Opheila finally began to weaken as it turned to the north-northeast, reaching a forward speed of 30 mph north of 35ºN latitude. The circulation slowly lost definition as it raced towards Newfoundland ahead of a cold front to its west.

That night, Ophelia lost most of its remaining tropical characteristics, weakening to a tropical storm during the morning of October 3. Any central convection still associated with the system vanished as Ophelia made landfall in the Avalon Peninsula, and the system became extratropical. The cyclone continued northeastward until dissipating on October 5. Minimal damage was the only effect of Ophelia, with no fatalities occurring.



Hurricane Ophelia nearing peak intensity as a Category 4 hurricane.



Track of Ophelia, including time spent as an non-tropical system before reforming.

Hurricane Nate (2011)

Storm Active: September 7-11

After Tropical Storm Lee became extratropical over the southeast U.S., an extension of its associated frontal boundary dipped into the southern Gulf of Mexico. On September 6, the interaction of this front with a trough of low pressure caused a low pressure system to form in the Bay of Campeche. Over the next day, the low hardly moved, and organized rapidly. On September 7, the low-level circulation of the low became more well-defined and the system was upgraded into Tropical Storm Nate.

Nate formed with a very slow motion to the southeast, and did not move significantly overnight. Despite a low shear environment, there was one inhibiting factor to strengthening: a large area of dry air to the system's northwest, occupying the entire northern Gulf. During the day of September 8, the center drifted further southeast, becoming closer to the convection, which had been displaced to the southwest of the center by moderate wind shear. Nate was sheltered somewhat, and strengthening commenced. By the evening of that day, Nate was completely stationary, and at its peak intensity of 75 mph and a pressure of 994 mb*.

Dry air entered the system during the early morning of September 9, however, and weakening took place. Later that day, Nate began to move slowly northwest, away from the Yucatan Peninsula, as further weakening occurred. By the morning of September 10, rainbands had recovered somewhat on the periphery of the cyclone, but the center remained devoid of convection, giving Nate a hollow appearance. The tropical storm finally adopted a definite motion later that day, moving due west. As it did so, conditions improved slightly and re-strengthening occurred afternoon. Nate reached its secondary peak intensity of 65 mph winds before convection decreased once again early on September 11.

The position of the center became very uncertain as Nate approached the Mexican coast, and the definition of the circulation decreased, lowering Nate's intensity to only 45 mph as it made landfall in Veracruz. The cyclone quickly weakened to a remnant low that night. Not much convection was associated with Nate over its lifetime, but its slow movement still allowed prolonged periods of gusty winds and rain along many parts of the coast of the Bay of Campeche. 7 fatalities were the result of Nate.

*Nate was upgraded to a hurricane during the 2011 postseason analysis, its maximum winds having previously been recorded as only 70 mph.



Tropical Storm Nate at peak intensity on September 8. At this time, Nate was nearly stationary.



Track of Nate.

Hurricane Maria (2011)

Storm Active: September 6-16

On September 4, a tropical wave off of the African coast began to generate shower activity south of the Cape Verde Islands. This activity became more widespread and more organized with the westward moving wave on September 5, as surface pressures began to drop over the region. A low pressure center developed in association with the wave that day, and the circulation became closed on September 6, announcing the formation of Tropical Depression Fourteen. The depression slowly organized over the next day, as it moved quickly west-northwest. A rapid intensification occurred during the morning of September 7, as an area of deep convection appeared northeast of the center, and the cyclone was upgraded to Tropical Storm Maria, with 50 mph winds.

High wind shear affected the system from its formation, however, and a powerful ridge to Maria's north imparted it with an extremely rapid westward motion of 23 mph during the night and into the morning of September 8. The storm struggled to maintain a circulation during the afternoon, and began to weaken as a result. All but minimal central convection disappeared during the early evening, and Maria became a minimal tropical storm. Overnight, however, a huge area of convection appeared. Despite this new thunderstorm activity, Maria did not intensify significantly on September 9, as the low level center was ill-defined and difficult to locate on satellite imagery.

On September 10, all convection was displaced to the northeast of the center by wind shear. So although being in close proximity to the northeast Caribbean Islands, the storm caused nearly no rain there as Maria moved northwest. The cyclone began to recover organization once again during the morning of September 11, and became a strong tropical storm as it moved west-northwest past the U.S. Virgin Islands that afternoon. A powerful trough coming off of the United States east coast started to affect Maria that evening, and it took a turn to the north on September 12, though slowing to nearly stationary. On September 13, the system began to accelerate, and finally moved away from the upper-level low that had been affecting it for so long with wind shear.

The center of Maria reformed within an area of deep convection late that night, and banding features increased in organization. During the morning of September 14, intensification began, and shear decreased. The decrease was gradual, however, and no further change occurred during the afternoon. By this time, Maria had turned to the north-northeast and already was accelerating extremely rapidly. Conditions in Bermuda deteriorated late that night and into the morning of September 15, as Maria passed to its west at near hurricane strength. Deep convection appeared near the eye that afternoon, and an eye structure began to form. Maria was therefore upgraded to hurricane status.

That night, Maria reached its peak intensity of 80 mph winds and a pressure of 979 mb. During the morning of September 16, the cyclone's forward speed exceeded 50 mph. Its closed circulation vanishing, Maria made landfall in Newfoundland as a minimal hurricane on the cusp of extratropical transition that afternoon, followed by absorbtion by a front a few hours later.



Hurricane Maria moving rapidly northward. The cyclone is already exhibiting some extratropical traits.



Track of Maria.

Tropical Storm Lee (2011)

Storm Active: September 1-4

During the day of August 30, shower activity increased with a tropical wave moving west-northwestward through the western Caribbean Sea. Meanwhile, a stationary low pressure trough was situated over the Gulf of Mexico. During the next few days, the tropical moisture of these two systems combined, forming a very large area of strong thunderstorms over the eastern Gulf, stretching from the Yucatan Peninsula to Florida. Shear from the west affected the system, but began to slowly abate during the day of September 1. During that afternoon a circulation appeared on the western edge of the clouds, becoming closed by the evening. Tropical Depression Thirteen had formed.

During the night, the depression's center reformed farther south and lost nearly all of its initial motion to the northwest, Due to weak steering currents, the system remained nearly stationary through the morning of September 2. Also, an area of deep convection developed near the center, despite the center itself remaining rather elongated. Due to the system's large size, rain and gusty winds already were moving into southeastern Louisiana. The circulation of the system became more well-defined that afternoon, and Thirteen became Tropical Storm Lee.

Lee had an unusually large windfield even at the time of its formation, and it continued to expand later that day. The cyclone itself also slowly strengthened, moving erratically, but generally northward. Lee still exhibited some characteristics of a non-tropical cyclone even into September 3, with the southwest quadrant still devoid of convection. During that morning, heavy rain continued across Louisiana and Mississippi, and tornadoes were reported within the heaviest bands, located in southern Louisiana.

Lee strengthened further as it slowly moved toward the Gulf coast, reaching its peak winds of 60 mph during the day. However, a second low-level center developed within the system early that afternoon, the original over land, and the second still off the coast. The new formed center took over the circulation while the other dissipated, and Lee therefore stalled off of the coast of Louisiana, with tropical storm conditions still extending far inland all across the central Gulf states. During the night, convection decreased, with the only rain band near the center extending to the southwest. Gradual weakening occurred, but Lee still did not assume any definite motion, and was still hovering over the coast, continuing the already severe flooding of the surrounding areas. Despite the winds having fallen, Lee's central pressure decreased to 987 mb early on September 4. The system finally made landfall in Louisiana later that morning.

The circulation actually became better defined for a brief period over land that afternoon, but the cyclone quickly degenerated, weakening further that evening, and began extratropical transition late that night. The system was fully extratropical by the next day, but the rain was by no means over. During the day of September 5, the remnants of Lee combined with a powerful cold front. With the addition of tropical moisture, a region of heavy rain formed from the tail end of Lee, in Louisiana, through the end of the front, in Canada! Lee's remnants lost their well-defined center on September 8, but rainfall continued for two more days, finally ending on September 10. The several days that Lee spent moving up the coast saw unprecedented flooding in the the mid-Atlantic states, New England, and even in some areas as far north as Canada. Rainfall totals from the combined storm system exceeding 6 inches in widespread areas, with local amounts significantly greater. 21 fatalities resulted from Lee, along with over $250 million in damages.



Lee strengthening over the northern Gulf of Mexico.



Track of Lee.

Note: In post-season analysis, Lee was confirmed to have been subtropical from September 3 up to the points of extratropical transition. This means that the cyclone transitioned from tropical to subtropical, a very rare event.

Hurricane Katia (2011)

Storm Active: August 29-September 10

A low formed just off of the African coastline on August 27, associated with a tropical wave, and was already showing signs of organization. The broad area of showers and thunderstorms quickly became concentrated over the next day, as the system passed well south of the Cape Verde Islands. Rapid development continued, and the system became Tropical Depression Twelve early on August 29. The depression also formed at 9.4º N, fairly far south for a tropical cyclone. Some shear out of the east affected the system from the beginning, and, as a result, the center remained on the eastern tip of the cloud cover through the day, A ore circular area of convection developed early on August 30, and although shear continued, the system was organized enough to be named Tropical Storm Katia.

Katia adopted a west-northwest motion that morning, and also accelerated somewhat in forward speed. Through the day, shear lessened significantly, and Katia began to rapidly intensify. Deep convection had enveloped the center by that afternoon, and Katia quickly became a strong tropical storm that evening. The intrusion of dry air on the circulation delayed intensification overnight, but Katia resumed a slow strengthening trend by August 31. Meanwhile, the cyclone moved even faster to the west-northwest, under the influence of a ridge to its northeast, its forward speed exceeding 20 mph. Katia continued to slowly organize, and the development of a well-defined eyewall merited the upgrade of the system to a hurricane late that night.

However, some dry air entered the circulation from the south, temporarily weakening the eyewall early on September 1, and causing the cyclone to stabilize in intensity. Katia also returned to a westerly motion that morning. However, shear increased during the day from an upper-level low to Katia's north, due to the close proximity of the low, and Katia again became disorganized weakening back to a tropical storm. A deeper burst of convection appeared with the system early on September 2, but the center remained on the periphery of this cloud cover during the early morning hours. Katia decelerated significantly, and turned once again to the west-northwest. Despite somewhat hostile conditions, Katia regained hurricane status later that morning, as a gradual turn to the northwest began.

Katia continued to struggle against wind shear throughout the day, and even developed an eye for a time that evening! However, the eye remained too close to the edge of convection to survive, and clouded over early on September 3. The cyclone's central pressure dropped, and Katia maintained minimal hurricane intensity. Thunderstorm activity decreased in the eastern half of the circulation that afternoon, and the cyclone became slightly lopsided. As a result, Katia again weakened to a tropical storm. Later in the evening, the fluctuations in intensity continued, as convection once again increased, and another eye formed. Due to this, Katia was once again upgraded to a hurricane during the morning of September 4. Through the night, Katia had still maintained a general northwest motion.

Later that morning, a well-defined eye developed, and Katia underwent rapid strengthening, becoming a Category 2 hurricane. That afternoon, Katia reached an intensity of 105 mph winds and a pressure of 965 mb. However, dry air invaded the system once again, this time from the northeast quadrant, and Katia weakened slightly during the early morning of September 5. Rather than disrupting the circulation in the long term, however, the dry air was incorporated into a large eye that appeared later in the morning. Katia once again strengthened rapidly, as outflow also improved that afternoon. Following these structural changes, the cyclone was subsequently upgraded to a major hurricane. Further intensification ensued late that evening, and Katia quickly reached its peak intensity as a Category 4 hurricane, with 135 mph winds and a pressure of 946 mb.

However, as the storm continued northwest, it began to encounter less favorable conditions, including lower ocean temperatures, and increased wind shear. A general weakening trend began, and Katia soon lost Category 4 status. The hurricane force wind field remained quite broad, though, and even became larger during the morning of September 6. These winds extended up to 55 miles from the center that afternoon. Rip currents and high surf were already beginning to affect Bermuda, and the threat increased on September 7. In the face of dry air and wind shear from the west, the circulation became more lopsided, with any remaining symmetry in the eyewall disappearing by that morning.

Bermuda also received gusty winds and scattered showers, being on the periphery of Katia's powerful east side. By that afternoon, the cyclone's winds had decreased to 85 mph, a Category 1 intensity. A turn to the north followed during the early evening hours, and Katia's forward motion increased. Despite moving into cooler waters, the upper atmospheric conditions near Katia improved that night and it strengthened slightly as it recovered the western half of the eyewall somewhat. The system made its closest approach to Bermuda the following morning, passing well to the west. Once again, Katia's convection actually increased over cool waters during the day of September 8. A turn to the northeast commenced that evening, and Katia's motion rapidly increased. By September 9, the cyclone was speeding away from the New England coast. Extratropical transition began later that day, and Katia finally became extratropical during the morning of September 10, after reaching a forward speed of over 50 mph.

At the time of the last advisory, Katia still packed winds of 80 mph, and became a powerful extratropical cyclone, impacting north portions of the British Isles on September 11 with high winds and rain as it passed to the north. Katia indirectly affected the Lesser Antilles, Bermuda, the east coast of the United States, and the United Kingdom. 2 fatalities, one direct and one indirect, were the result of Katia.



Katia near peak intensity as a Category 4 hurricane.

Tropical Storm Jose (2011)

Storm Active: August 28-29

On August 19, a tropical wave moved off of Africa, and was immediately monitored for development upon leaving the coast. A broad low pressure system quickly formed in conjunction with the wave, and convection increased, but despite favorable conditions, no closed circulation formed as the system passed near the Cape Verde Island on August 20. The low's circulation became elongated during the day of August 21, and it moved northwest, into cooler waters. THe system did not dissipate, however, and still produced some shower activity over the next few days. The low elongated further on August 25, and degenerated into a trough of low pressure. This trough interacted with another to its west, and a weak low formed from this union on August 27, now located south-southeast of Bermuda. The low deepened and moved generally northwest, but very high shear from the outflow of Hurricane Irene ripped convection from the low faster than it could form. Despite these extremely hostile conditions to tropical development, the circulation, although being nearly devoid of convection, became closed, and gale force winds in the low's southeast quadrant caused it to be named Tropical Storm Jose during the morning of August 28.

Due to its proximity to Bermuda, a tropical storm warning was issued there. Against all odds, Jose's southern side developed some deep convection that afternoon and the system strengthened slightly as it moved north, past Bermuda, and reached its peak intensity of 45 mph winds and a central pressure of 1007 mb. Overnight, Jose accelerated northward and was weakening by the morning of August 29, as it encountered cooler waters. By later that day, the circulation no longer existed, and Jose dissipated, downgraded to a trough of low pressure. In the wake of Jose, to its south, large areas of thunderstorms appeared near Bermuda for the remainder of the day, partly having their origin in tropical moisture from the cyclone, which was displaced to the south by shear. Therefore, Jose indirectly caused some minimal damage to Bermuda.



Track of Jose.

Tropical Depression Ten (2011)

Storm Active: August 25-26

During the afternoon of August 22, a low pressure system moved into the Atlantic off of the African coast. The circulation of the low was not yet well-defined, but it slowly moved west-southwest over the next few days, gaining convection and organization as it went. As the low passed to the south of the Cape Verde Islands, scattered showers occurred there. By August 24, the system was moving west away from the islands, and was quickly organizing. Early on August 25, a well-defined circulation developed, and the existence of a rain band circumnavigating the center, confirmed the formation of Tropical Depression Ten.

Initially, the depression seemed on the verge of tropical storm strength, but as it tracked west-northwest, the convection decreased, and was minimal by later in the morning on August 25. Despite a return of convection during the day, the circulation became elongated, and badly defined. This trend continued into August 26, keeping the cyclone at tropical depression intensity. Winds near gale force still appeared periodically, but the circulation became so stretched that the depression no longer met the standards of a tropical cyclone by later that night. Tropical Depression Ten officially degenerated into a trough near midnight, losing its definition entirely by August 27. The cyclone affected no land masses, with the exception of a few storms in the Cape Verde Islands.



Tropical Depression Ten over the east Atlantic.



Track of Tropical Depression Ten.

Hurricane Irene (2011)

Storm Active: August 20-29

On August 15, a tropical wave moved off of Africa, but dry air near the system did not allow significant development. However, on August 17, a small area of convection formed in associated with the wave, followed by a low pressure center on August 19, when a definite circulation appeared in the clouds. Pressure in the area began to fall overnight, but no surface circulation had yet formed. During the evening of August 20, however, rapid intensification occurred, and a very organized surface circulation appeared. Hurricane hunter aircraft found winds high enough for the system to skip the tropical depression stage, and the low became Tropical Storm Irene, packing 50 mph winds even at its formation!

Early on August 21, Irene moved over the Lesser Antilles, and, being a fairly large cyclone, caused gale force winds and tropical storm conditions over a wide area as it entered the Caribbean. The cyclone was still moving westward at a fast clip, with its forward speed exceeding 20 mph. Irene maintained its intensity throughout the day, and made landfall in Puerto Rico that evening, causing heavy rain and very strong winds over the entire island. Despite some interaction with land, Irene rapidly strengthened, its circulation and outflow improving greatly that night. A huge burst of convection engulfed the system early on August 22, and the cyclone became Hurricane Irene, the first hurricane of the 2011 season.

Irene decelerated during the morning, and continued to move west-northwest, leaving Puerto Rico, where over 10 inches of rain fell in localized areas. The eyewall developed further during the evening of August 22, and the Irene rapidly intensified into a Category 2 hurricane with 100 mph winds as it passed just to the north of the Dominican Republic, with tropical storm conditions covering much of the country, and gusts of hurricane force on the northern coasts. Irene slowed down even more during the morning of August 23, with a forward speed of 10 mph to the west-northwest as it approached the Bahamas.

Later in the morning, a ragged eye appeared, and the central pressure of Irene dropped slightly. However, it was not a well-formed structure, and it clouded over in the afternoon, causing a weakening not uncharacteristic of eye replacement, putting the system back to a Category 1 intensity. Land interaction decreased considerably as Irene moved away from Hispaniola during the evening, convection returned in earnest, the central pressure dropped further, and another, more organized eye appeared. The cyclone soon regained its lost strength, and then intensified further, as it encountered the Turks and Caicos Islands during the morning of August 24. The system's winds surpassed 110 mph that same morning, and Irene became the first major hurricane of the season, with 115 mph winds and a pressure of 957 mb.

By later in the day, Irene had entered the Central Bahamas, the eye was tightening, and a new eyewall was forming. As a result of this, the eye began to cloud over, causing fluctuations in intensity. However, the system remained a Category 3, and the central pressure continued to steadily drop. Irene maintained its northwest motion into August 25, as surf began to increase along the U.S. coast. Later in the day, Irene finally left the Bahamas, and made a turn northward, toward the Outer Banks of North Carolina, early on August 26. The pressure of the cyclone dropped to 942 mb, the lowest yet for the cyclone, but another eye replacement weakened the system, decreasing its wind speeds to that of a Category 2 hurricane.

Rain bands from Irene were already beginning to sweep across the U.S. east coast from Florida up through the Carolinas. The internal structure of Irene remained slightly disorganized, and gradual weakening occurred as conditions became less favorable for intensification. Powerful outer bands packing tropical storm force winds penetrated into North Carolina through the day. Late on August 26, the convection became rather lopsided, with the southwest quadrant weak, and Irene subsequently weakened to a Category 1 hurricane early on August 27. Around 8:00 am EDT that morning, Hurricane Irene made landfall with 85 mph winds in eastern North Carolina, just west of the Outer Banks.

The cyclone began to assume a more asymmetrical appearance that afternoon, with most of the rain extending northward, reaching even Pennsylvania and New Jersey by early afternoon. The circulation, however, actually increased in definition as the day wore on. The forward speed of Irene finally began to increase that evening, but the cyclone moved steadily north-northeast, and emerged over water once again later that night, paralleling the Virginia coastline. Dry air entered Irene's southern side, and weakened it slowly through the morning of August 28, as the center of the hurricane made landfall in New Jersey before sunrise. At the time, the cyclone had weakened to a strong tropical storm, with 70 mph winds.

The windfield of the storm, however, was larger than ever, as tropical storm force winds spanned portions of 8 states. During the morning, Irene began to rapidly accelerate to the north-northeast, while quickly transitioning to an extratropical cyclone. By this time, all precipitation associated with Irene was on its north side, with the exception of one rain band, which protruded to the southwest, and affected areas as far south as Maryland even into early afternoon. The cyclone weakened to a tropical storm before making landfall in New York City that same morning. Irene persisted in the same general motion throughout the day, still bringing gusty winds to much of the northeast, before finally becoming extratropical near the U.S. border with Canada late that night. Rainfall continued in Canada as the remnants of Irene continued speeding northeastward, and the low emerged into the north Atlantic on August 30, passing near Greenland by the next day.

Irene had a devastating impact on areas from the Lesser Antilles to Vermont, and caused between 10 and 20 inches of rainfall locally in all regions along its path. The Bahamas, in particular, suffered high wind damages, as Irene was at peak intensity over the islands. Damage is estimated at $10.1 billion, and 54 fatalities resulted from the cyclone. Irene was also the first storm to make landfall in the U.S. at hurricane intensity since Ike of 2008.



Irene as a major hurricane entering the Bahamas.



Track of Irene on its path through the Caribbean, the Bahamas, and along the east coast of the United States.

Tropical Storm Harvey (2011)

Storm Active: August 18-22

On August 10, a vigorous tropical wave emerged off of Africa, and immediately began to produce an area of concentrated thunderstorms southeast of the Cape Verde Islands. On August 11, the system became more organized as a low pressure centered formed. However, the dry air of the eastern Atlantic penetrated the system, and cloud cover rapidly decreased as the low degenerated back into a tropical wave. The wave continued its journey westward, and convection once again erupted over a large area surrounding the system as it entered the moist waters near the Lesser Antilles. A broad upper-level circulation developed on August 16, but the system lacked a surface low, which inhibited further development as it entered the Caribbean Sea. The system moved due west for another few days before developing a surface low late on August 18, and being classified Tropical Depression Eight.

Eight was already producing rain and wind near the Honduras-Nicaragua border at formation, and conditions worsened on the northern coast of Honduras as the cyclone paralleled this coast, just a few miles offshore. Despite its proximity to land, the system developed deep convection and rain bands about the center, and a jog northeast on August 19 made conditions more favorable for strengthening as the day went on. A well-defined eyewall appeared on the south and west sides of the center during the afternoon, and Eight was named Tropical Storm Harvey shortly after.

The cyclone continued on a westward track through the evening of August 19, and strengthened rapidly, reaching an intensity of 65 mph winds and a pressure of 994 mb before temporarily stabilizing in intensity early on August 20. Since the tropical storm force winds extended only about 20 miles south of the center, (they extended 35 miles north at the time) gale force winds missed Honduras for the most part, although heavy rain fell throughout the region. Harvey continued to maintain the above peak intensity through landfall in Belize, which occurred that afternoon.

After landfall, Harvey continued to move west to west-northwest, and maintained a tropical storm intensity for an impressive 12 hours before weakening into a tropical depression over northern Guatemala. Thunderstorm activity continued throughout the region even as Tropical Depression Harvey crossed from inland Guatemala into inland Mexico on August 21. Later that day, the center, which was still well-defined, jogged to the north, and the depression emerged over the Bay of Campeche. With this new found access to water, Harvey strengthened slightly, but did not regain tropical storm intensity before making a turn to the west-southwest and making landfall in the southern Gulf coast of Mexico early on August 22.

Harvey quickly weakened as it moved inland, and dissipated later that morning. Only minimal damage was sustained, but 3 fatalities occurred from flooding, as Harvey dumped many inches of precipitation over Central America. Since Harvey did not reach hurricane strength, the record of consecutive named storms to not became hurricanes to start the season was extended to eight.



Tropical Storm Harvey shortly after formation.



Track of Harvey.

Tropical Storm Gert (2011)

Storm Active: August 13-16

On August 10, a trough of low pressure developed over the Central Atlantic, associated with a low pressure system to its north. Over the next two days, the low center accelerated northeast, leaving the trough in its wake. The trough formed another weak low pressure center on August 12, as it drifted to the west-southwest at around 10 mph. The convection associated with the low remained very disorganized during the day, but the circulation became more well-defined on August 13, despite the center being partially exposed. More shower activity developed developed later that day, and a deepening of the low sparked the formation of Tropical Depression Seven late that night.

Deeper convection appeared overnight, and Seven intensified into Tropical Storm Gert as the cyclone made a turn to the north on August 14. The outflow of the system improved and the circulation assumed a more rounded appearance early on August 15, and rapid strengthening followed as the cyclone approached Bermuda. Gert reached peak intensity of 65 mph winds and a pressure of 1000 mb later that day. During the afternoon, Gert began a turn to the northeast, passing well to the east of Bermuda, and causing only minimal damage. The cyclone then began to accelerate further, and dry air permeated the system, weakening it overnight and into August 16. Gert quickly lost organization, and was an extratropical cyclone by later that day. Since Gert passed well east of Bermuda, no damage was sustained on the island. Additionally, since Gert did not achieve hurricane status, 2011 became the only year on record in which the first seven named storms did not become hurricanes.



Gert near peak intensity east of Bermuda, on which the cyclone had only minimal impacts.



Track of Gert.

Tropical Storm Franklin (2011)

Storm Active: August 12-14

On August 10, a large trough of low pressure formed over Florida, with shower activity extending both east into the Atlantic, and west into the Gulf of Mexico. This activity moved generally to the northeast and interacted with a front moving off of the east coast. During the morning of August 12, convection concentrated at a low pressure center on the front, but the elongated nature of the frontal low kept it extratropical through the morning. As it accelerated away from land, the low became well-defined, and became disconnected from the front. As a result, Tropical Depression Six formed that afternoon, just north of Bermuda.

The effects on the island were only to the extent of scattered showers and gusty winds, as Six was tracking quickly away to the northeast. By the morning of August 13, the presence of deep convection within the system allowed it to intensify into Tropical Storm Franklin. Through the morning, thunderstorm activity with this tropical storm continued to increase, and outflow improved in all quadrants, despite increasing shear. Following this increase in organization, Franklin reached its peak intensity of 45 mph winds and a central pressure of 1004 mb during the day. However, Franklin was quickly approaching colder waters, and rapid weakening ensued that evening. By the following morning, Franklin had become extratropical. The remnant low of Franklin tracked east, and was quickly absorbed. The cyclone affected no land.



Tropical Storm Franklin over the open waters of the northwest Atlantic.



Track of Franklin.

Tropical Storm Emily (2011)

Storm Active: August 1-7

An intense tropical wave left the African coast during the last week of July, producing a large area of scattered showers and thunderstorms as it moved westward. On July 28, a low pressure center formed on the south side of the system. The low continued to increase in organization, and on July 31, the circulation became associated with the convection in a pronounced swirl of clouds. However, the system was not yet closed, and development was delayed as the low approached the Windward Islands. During the evening of August 1, a burst of convection appeared west of the central low's previous position, accompanied by a circulation organized enough to name the system Tropical Storm Emily.

Due to the initial westward shift of the cyclone, its position at formation was west of the Windward Islands, in the Caribbean Sea. Emily's quick westward motion persisted overnight, bringing the system into the warm open waters of the Caribbean. However, conditions were not ideal for strengthening due to wind shear and dry air near the system, and Emily's center underwent a reformation on August 2, temporarily rendering it stationary. After shifting slightly to the north, the cyclone resumed its track and intensified somewhat as it approached Hispaniola.

Emily became disorganized during the morning of August 3, with the center of circulation becoming exposed and all convection being displaced to the southeast due to moderate wind shear. Despite these factors, Emily maintained its 50 mph intensity throughout the day, and scattered shower and thunderstorm activity reappeared near the center. As a result, heavy rain began to sweep across Haiti and the Dominican Republic. Late that night, the center redeveloped farther east, and Emily was once more temporarily stationary. A huge area of convection appeared about the center as Emily resumed a slow west-northwest motion, and powerful storms raged across Hispaniola early on August 4. The system remained offshore during that morning, but tropical storm force winds and rain covered a portion of the Dominican Republic.

During the afternoon, however, the circulation of Emily became entangled with the mountainous regions of Haiti, causing rapid weakening. By late that afternoon, despite never actually making landfall, all traces of organization were lost and Emily dissipated, leaving only a small trough of low pressure in its wake. The remains of the large area of convection that was formerly associated with Emily slid northward over Hispaniola and into the Bahamas overnight, but some thunderstorm activity reappeared near the trough on August 5, situated just to the south of the eastern tip of Cuba. This activity expanded northward during the day as a low pressure reformed just east of Florida. On August 6, the system became more organized, as the low connected to the new convection, and the low once again became a tropical depression, again being named Emily.

The depression became slightly better organized during that evening, but turned more to the northeast overnight, and the circulation became exposed on August 7 as the center was whisked away from the U.S. east coast. Emily continued to lose organization, and during the afternoon became a remnant low, losing tropical cyclone status once again. Over the next day, the low deepened, and briefly concentrated convection near the center, but it did not exhibit sufficient tropical characteristics to reform. The system was monitored for further development through August 11, but no change occurred, and the remnant low was finally absorbed by a front later that day. 5 deaths and at least $5 million in damages are attributed to Emily.



Emily near its peak intensity of 50 mph winds and a central pressure of 1003 mb.



Track of Emily.

Tropical Storm Don (2011)

Storm Active: July 27-30

Around July 17, a vigorous tropical wave emerged off of Africa, quickly associating convection with it as it tracked over the open Atlantic. On July 22, it began to affect the Lesser Antilles with areas of heavy rain, and briefly developed a low pressure center. However, a small area of unfavorable wind shear passed over the system, and it remained disorganized. Development was hampered further on July 24, as the wave passed directly over the Dominican Republic and Haiti. During the next few days, this was followed by interactions with Jamaica and Cuba, which kept thunderstorm activity to a minimum. However, on July 26 the wave moved over the waters of the Caribbean south of Cuba. Slow organization occurred over the next day, and by July 27, a low pressure center had formed. During that morning, however, the low lacked a closed circulation and the convection was divided into two hemispheres, with the area of low pressure not directly associated with any one part of the system. Finally, during the afternoon of July 27, a circulation became evident at the northern tip of the system's western half, and the low was upgraded to Tropical Storm Don just north of the Yucatan Peninsula.

A ridge of high pressure to the northeast of Don steered it in a generally northwestward course through the Gulf of Mexico. Over the next day, convection increased, particularly on the southern side of the circulation, and modest strengthening occurred despite shear and dry air from the north. On July 29, the ridge became stronger, and turned Don more to the west-northwest, toward southern Texas. During that day, Don reached its peak intensity of 50 mph and a minimum pressure of 997 mb. The presence of Don generated significant tropical moisture along the northwestern Gulf coast, including Louisiana and parts of Texas. However, as the system made landfall, most rain was concentrated near the center and on the south side, and southernmost Texas therefore received the most rain. Tropical storm force winds enveloped a larger area of the coast, but quickly diminished as Don made landfall. Over land, the system weakened rapidly to a remnant low, causing no damage or fatalities.



Don near peak intensity shortly before landfall in Texas.



Track of Don.

Tropical Storm Cindy (2011)

Storm Active: July 20-23

On July 19, a low pressure center formed along a stationary frontal boundary situated over the central Atlantic, in the vicinity of Bermuda. This front was the same one that spawned Tropical Storm Bret. The low quickly moved to the east, and deepened over the next day. On July 20, its circulation became increasingly disassociated with the frontal boundary, and the appearance of deep central convection was enough to name the system Tropical Storm Cindy that afternoon.

Even as it formed, it began to accelerate northeastward at speeds over 20 mph. Cindy strengthened rapidly as the circulation became better defined, developing a proto-eye feature early on July 21. The cyclone reached its peak winds, 70 mph, during that morning, and maintained its tropical characteristics through the day. The winds began to decrease as Cindy passed over the cold water north of the 40ºN parallel, but the pressure dropped from 1002 to 1000 mb. Additional drops in pressure despite negative changes in wind speed is often a symptom of a cyclone entering extratropical transition, which Cindy did on July 22. However, Cindy's convection was rapidly deteriorating by that afternoon, and the system continued to weaken, becoming a minimal tropical storm by late that night. Cindy was downgraded to a remnant low before actually becoming extratropical early on July 23. The remnant low of Cindy dissipated later the same day, causing no damage.



The low pressure system that formed Cindy mere hours before being classified as a tropical storm.



Track of Cindy.

Tropical Storm Bret (2011)

Storm Active: July 17-22

Following the departure of a cold front from the U.S. east coast, a west-to-east situated stationary front stalled over the Florida coast and adjacent Atlantic waters. On July 16, a weak low pressure center formed in association with this front, and produced an area of showers and thunderstorms off of the eastern Florida coast. The pressure of the system remained high as it drifted slowly southward over the next day, but a clearly defined closed circulation formed during the afternoon of July 17, and the low was upgraded to Tropical Depression Two. Further deepening quickly followed, and the cyclone achieved tropical storm status a mere three hours later.

The newly formed Tropical Storm Bret experienced almost no motion overnight, drifting southward and then eastward, all the while meandering over the Northern Bahamas. Despite some wind shear out of the west that was bringing dry air into the system, convection persisted, and even developed during the morning of July 18, and the strengthening trend continued. Bret even developed a ragged eye amidst its tight circulation that evening, reaching a strong tropical storm intensity of 70 mph winds and a minimum pressure of 995 mb.

However, dry air penetrated the system late that night, causing weakening as the cyclone continued to move slowly north-northeast. As Bret paralleled the southern portion of the U.S. east coast early on July 19, nearly all convection was lost, and the system packed winds of only 50 mph. Some convection returned that morning, and Bret managed to maintain its intensity despite increasing shear from the northwest. With the exception of the southeastern quadrant, which contained some cloud cover, but even it was struggling, Bret had no associated convection whatsoever, and was essentially a bare circulation. Bret moved northeast through the day, and even into July 20 maintained the same intensity, despite very adverse conditions.

The storm finally began to weaken again that evening as it moved over slightly cooler waters, becoming a minimal tropical storm by July 21. Late that night, the storm was downgraded to a tropical depression while located between the Outer Banks of North Carolina and Bermuda. It also underwent significant acceleration to the northeast, reaching speeds over 20 mph. Yet despite the lack of convection, the system persisted as a tropical cyclone through most of July 22, and finally degenerated into a remnant low that afternoon. Bret's only effects were scattered storms and gusty winds in the northern Bahamas.



Bret at peak intensity just northeast of the Bahamas.



Track of Bret.

Tropical Storm Arlene (2011)

Storm Active: June 28-30

Arlene originated from one of many tropical waves emerging off of the west coast of Africa during late June. On June 25, this particular wave, at the time moving onto the Yucatan Peninsula, began to interact with a broad trough of low pressure over Central America and the waters to the north. This interaction generated an area of scattered showers and extending westward from the wave itself into the western Caribbean Sea. The next day, on June 26, the wave moved over the central Yucatan, and thunderstorm activity concentrated along it, extending from north to south. On June 27, the wave emerged into the Bay of Campeche, and immediately rain bands began to form about a low pressure center in the southeasternmost area of the Bay, just north of the Mexican coast. The low tracked slowly west-northwestward and strengthened, but upper level winds were not yet favorable, and the circulation was not yet well-defined. However, wind shear diminished further on June 28, and the low was upgraded to Tropical Storm Arlene that evening.

Arlene maintained a slow west-northwest motion overnight, and the rain bands, formerly being sparse, quickly increased in convection early on June 29. The cyclone, which had only minimal tropical storm strength up to this point, intensified as it turned more to the west. By later that day, rain and wind began to sweep across the Mexican coast. Despite its proximity to land, Arlene's winds continued to increase, and the cyclone reached its peak intensity of 65 mph winds and a minimum pressure of 993 mb just before landfall near Cabo Rojo, Mexico. Before losing its water supply, which provided fuel for Arlene's convection, it also developed an eye-like feature.

After landfall early on June 30, Arlene began to quickly weaken over land, becoming a tropical depression that afternoon, and dissipating that evening. The remnants of Arlene caused rain in Mexico for an additional day before moving west into cold Pacific waters. The moisture from Arlene, although causing significant flooding in parts of northeastern Mexico, had a more positive effect on areas of Texas. In that state, numerous thunderstorm activity was generated by the trough associated with Arlene, temporarily relieving drought conditions. 25 fatalities, including 11 direct and 14 indirect, are associated with Arlene.



Arlene near peak intensity shortly after landfall in Mexico. Although a strong tropical storm, Arlene's center (and eye feature) are still not well defined.



Track of Arlene.

Professor Quibb's Picks-2011

My personal prediction for the 2011 Atlantic Hurricane Season (written May 15, 2011):

20 cyclones attaining tropical depression status
19 cyclones attaining tropical storm status
10 cyclones attaining hurricane status
6 cyclones attaining major hurricane status

These predictions are far above the average activity in the Atlantic basin. Several factors contribute to why I have made such a choice. First, the decade of 2000-2009 had shown far above average activity, including the record of most tropical cyclones in a single year (2005, 28 cyclones attaining tropical storm status). This general trend shows no sign of stopping as we enter the 2010's. Second, an ongoing La Nina event that contributed to the 20 tropical storms of the 2010 season is still active, reducing the amount of wind shear present over the Atlantic basin.

Also, I have made the number of hurricanes and major hurricanes quite high in relation to the overall number of cyclones. Last year, a large trough over the Gulf of Mexico prevented storms from tracking all the way through the Caribbean Sea and into the Gulf of Mexico, instead steering them into Central America. This inhibited their strengthening potential, and most landfalling systems were relatively weak. The only major hurricanes of the season meandered out in the open Atlantic. So far this year, there have been a fairly persistent US east coast high pressure systems, and these may serve to steer cyclones on more southward tracks, into the Gulf of Mexico. The Gulf is home to some of the Atlantic Basin's highest ocean temperatures, and in it is the potential for rapid intensification.

Finally, the tendency this year may be toward slower moving and longer lived systems, as the preliminary climatological signs point to weaker upper level steering systems, and the above argument appears to favor longer tracks over water. There is a great deal of uncertainty in slow moving cyclones, and, accordingly, there are many variables to be accounted for in the coming season. The 2011 seasons has the potential to be very active and damaging, but only time will tell whether this is actually the case.

The 2011 Atlantic Hurricane Season will officially begin on June 1, 2011.

Hurricane Names List-2011

For the Atlantic Basin, the hurricane names list for 2011 is as follows:

Arlene
Bret
Cindy
Don
Emily
Franklin
Gert
Harvey
Irene
Jose
Katia
Lee
Maria
Nate
Ophelia
Philippe
Rina
Sean
Tammy
Vince
Whitney

This list is the same as that of the 2005 Atlantic Hurricane Season, with the exceptions of Don, Katia, Rina, Sean, and Whitney, which replaced Dean, Katrina, Rita, Stan, and Wilma, respectively, as the latter were retired from the circulating names list in the same year.

Manifolds: The Shape of the Universe III

This is the final post of the Manifolds Series and the third concerning The Shape of the Universe (see the first of the entire series, or the first concerning The Shape of the Universe).

It was previously discussed that the constant Ω represents the ratio of the Universe's actual density to the so-called critical density which makes the Universe Euclidean. As of yet, the most accurate observation of the density of the observable Universe yields an Ω of 1.02, with a possible error of just over .02. This suggests that the Universe is most likely to be elliptic. However, none of the geometries can be eliminated yet, and other clues will most likely be required to definitively determine its shape.

At the moment, it seems that a Universe with an edge can be ruled out definitively, as the presence of boundary would disturb the isotropy (similarity of the view in each direction from any point in the Universe) which seems to be necessary for a Universe of constant density to form. Since this is most likely the case, a Universe with an edge can be ignored.

This leaves two possibilities. Either the Universe is infinite (no identical image points) or it is finite (with at least one image point in the night sky) but without boundary. The location and distance of these images would determine the shape of the Universe.

Take, for instance, that the Ω value is exactly 1.02, as predicted by current measurements. This implies an elliptic Universe. If the Universe is a 3-sphere, the leading theory for an elliptic structure, then a value of 1.02 would imply a radius of 98 billion light-years, meaning that, if one was to look 98 billion light-years into space, they would see the same view in every direction, namely the diametrically opposite pole. In other words, an expanding ball of space in the Universe would first intersect itself when it reaches this radius, known as the injectivity radius for the given Universe. These similar images in all directions would be very easy to spot, as they would be of the same distance, and therefore the same age.

However, for this particular value of Ω, these images are beyond our ability to see. The Universe is only about 13.7 billion years old, and we can therefore only see that far. Despite this, the most distant objects are seen as they were billions of years ago, and they actually have moved farther away since then. Extrapolating backward from the current rate of expansion, one finds that our observable Universe actually measures 46 billion light-years in radius. Although this is a significant portion of the previously discussed 3-sphere, it is by no means enough to identify the shape of the Universe through images.

One encounters interesting phenomena if the speed of light is allowed to reach infinity in an idealized Universe, making it so that multiple images could be detected. If this was the case, the spacing and distance of images, and shape of the "shells" of the images would identify the manifold. Consider the example below.



In this particular case, images of the Earth can be seen in all directions, and all of the same age and appearance. This is because the speed of light is supposed to be infinite, and the light from all images instantly reaches Earth. Each exists at the center of a dodecahedral "cell", each of which, on its own, represents the entirety of the Universe. The other cells outside of the center one are images. The manifold in question is known as the Poincare dodecahedral space. This is an elliptic manifold with properties similar to that of the 3-sphere. Its construction is shown in detail below.



The fundamental polyhedron for the Poincare dodecahedral space is a dodecahedron, hence the name. This polyhedron has twelve faces, so each face can be connected to the one opposite from it. However, to pair any face with its opposite requires a rotation of one of the faces, for they are not in the same orientation, despite being the same size. The faces are pentagons, and the opposite ones are misaligned by a 1/10 turn. Therefore, by first rotating the indicated face A counterclockwise by a 1/10 turn so that the A1 edges line up, one can connect the faces. This procedure is repeated for all of the pairs of opposite faces. Note that a 3/10 or 5/10 turn produces a completely different manifold! Therefore, choices of rotation and the choice of which pairs of faces are to be attached are both are crucial to determining a manifold.

With this construction in mind, further insight can be gained into the Poincare dodecahedral Universe shown above. It is now clear why the cells are dodecahedra, and that the distortion of these cells is by nature of the manifold being elliptic, as it does not "fit" into Euclidean three-dimensional space without distortion. Second possibly only to the 3-sphere, the Poincare dodecahedral space has the most following of any theory for the shape of an elliptic Universe.

For other geometries and manifolds, the image-finding method is even more difficult than that of the 3-sphere case. For a hyperbolic manifold of given curvature, the deviation of the Ω value from 1 produces a higher injectivity radius then an elliptic manifold of the same deviation, and Euclidean manifolds have images that are spaced unevenly and are at many different distances. (see also the discussion of the 3-torus Universe, found here)

Finally, observations of how forces, particularly gravity, affect objects may be helpful in determining the Universe's shape. At (relatively) small scales, when comparing stars, galaxies, and even superclusters, the gravitational pull of these massive objects distorts the local geometry of the Universe. However, when one considers the entire observable Universe, gravity's effect assumes a more uniform state.



To begin an analysis on how gravity's effect is determined by the shape of the Universe, is is useful to consider the mass distribution in its very early stages. The best source for this information is in the Cosmic Microwave Background Radiation. This radiation was emitted approximately 380,000 years after the Big Bang, by the matter present at the time, and, even at that stage, there were slight discrepancies in density and therefore temperature that gravity slowly molded into the structures we see today. The above image is of the temperature variances in this plasma, the precursor of all that we know in the Universe.

But exactly how did this process occur? Different universes and the gravitational differences between them have been analyzed in previous posts, but many of these properties were concerned with the effects of gravity traveling all around the Universe, and if it is of sufficient radius, these effects are not visible. Also, the most solid evidence thus far points to a lack of both images and these effects points to a Universe of very little curvature, if any. The local properties of our Universe closely resemble an infinite flat one, with just a hint of positive curvature.

In conclusion, the Universe is most likely to be elliptic, in the form of a 3-sphere, as this is the simplest of 3-manifolds, and it is not known how early Universe phenomena could have contributed to turning the Universe into a more complicated manifold, such as the Poincare dodecahedral space. The density measurements, with image and gravity evidence taken in mind yield an Ω probably between 1.01 and 1.02. The radius of the Universe is therefore very large, possibly over 100 billion light-years, and since this figure is constantly increasing, it is unlikely that the shape of the Universe can ever be determined through the image method alone.

The study of manifolds and topology is a broad and insightful area of mathematics that the above series of posts has only touched upon. The potential of manifolds in projection, mappings, the abstract and elegant constructions, and many other aspects of manifolds makes it an important area of study, which may even reveal what type of Universe we live in.

Sources: http://www.ams.org/notices/200406/fea-weeks.pdf, http://en.wikipedia.org/wiki/Homology_sphere#Poincar.C3.A9_homology_sphere,