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.