Tropical Depression Eleven (2018)

Storm Active: September 21-23

On September 18, a disturbance developed in the tropical Atlantic well east of the Windward Islands. It moved generally west-northwestward over the following view days and began to exhibit a small but organized canopy of thunderstorm activity. A weak low pressure center appeared on September 20, but wind shear increased significantly around the same time and the atmosphere was quite dry as the system approached the Caribbean. Despite unfavorable conditions, sheared convection persisted near the surface circulation center long enough the next day for the system to be classified Tropical Depression Eleven.

Before long, upper level winds out of the west increased even further, and any bursts of deep convection from Eleven were swiftly blown away. The center moved erratically the next day and began to lose definition, and by the morning of September 23, the system was downgraded to a remnant low. This low dissipated soon after.

Tropical Depression Eleven never achieved much organization during its brief lifetime.

The area of high wind shear over the Caribbean was persistent during the 2018 season, and claimed Eleven as another victim.

Tropical Storm Joyce (2018)

Storm Active: September 12-18

On September 11, a non-tropical low formed along a frontal boundary situated over the north central Atlantic, well west of the Azores. The low drifted generally southward or southwestward over the next day. By September 12, it was producing gale force winds and displayed some organized convective banding. However, the surface low was still colocated with an upper-level low, not the high found for tropical cyclones, so it was designated Subtropical Storm Joyce. Existing contemporaneously with Florence, Helene, and Isaac, the new system was one of four named storms simultaneously occupying the Atlantic basin. This was the first time this had occurred since 2008. Also, Joyce was the fifth subtropical cyclone of the season, the first time that had happened since 1969.

Shortly after formation, the cyclone felt the influence of the much larger Tropical Storm Helene to its southeast. Steered around the periphery of its circulation, Joyce moved west-southwest and then turned south around Helene's left side as it reached the same latitude. Meanwhile, on September 13, Joyce transitioned into a tropical storm. The next day, it strengthened slightly to a moderate tropical storm and turned eastward in the wake of Helene. This intensification was short-lived, however, as increasing wind shear out of the southwest stripped away the little convection that formed in bursts near the center of circulation. On September 16, Joyce weakened to a tropical depression.

The shallow system was left behind by now ex-Helene and instead followed the boundary of a mid-level high located in the subtropical Atlantic. This caused the depression to turn south of due east by September 17 and then south by the 18th. Late on September 18, Joyce had ceased to produce deep convection and was finally downgraded to a remnant low. The low moved slowly southwestward until dissipation.

The above image shows the small Tropical Storm Joyce as well as the edge of the larger Tropical Storm Helene to the east, which greatly influenced Joyce's motion.

Joyce did not affect any landmasses during its journey through the northeast Atlantic.

Hurricane Isaac (2018)

Storm Active: September 7-15

At the beginning of September, a tropical wave moved into the Atlantic. Though it was producing some showers and thunderstorms, but the disturbance remained disorganized for several days as it traveled westward. By September 5, the low had become better defined, but convection was quite limited near the center of circulation. On September 7, the disturbance was classified Tropical Depression Nine. That day, it also became nearly stationary as steering currents collapsed and it felt the pull of newly formed Tropical Depression Eight (which would become Helene) to its east. The center was nearly exposed at first due to shear, but the system's organization increased considerably on September 8. This prompted an upgrade to Tropical Storm Isaac.

The storm was very small, with tropical storm force winds extending only a few dozen miles from the center. Such storms are subject to rapid changes in intensity, and Isaac did gain strength quickly over the next day. Meanwhile, it finally picked up some forward speed toward the west. During the evening of September 9, it was upgraded to a hurricane. There was little change to the system over the next day, despite generally quite favorable conditions. The banding structure and core of Isaac struggled to improve, even with low wind shear. Soon, the satellite presentation became more ragged in appearance and the system was downgraded back to a tropical storm.

Early on September 12, an upper-level trough north of Isaac caused a sudden increase in shear on the system, quickly stripping convection away from the center. The cyclone began to rapidly weaken as a result. Nevertheless, it caused scattered heavy rains and tropical storm force winds as it passed among the Leeward Islands and entered the Caribbean during the morning of September 13. Thunderstorm activity started to make a comeback near the circulation center later that day, but the circulation itself was ill-defined and showed signs of becoming elongated. Isaac weakened to a tropical depression on September 14. Soon after, all traces of a closed circulation vanished and the storm dissipated. The remnants of Isaac brought scattered thunderstorms to Jamaica a few days later.

This image shows the small Tropical Storm Isaac moving over the open Atlantic.

Isaac dissipated shortly after entering the eastern Caribbean. This is a quite common event and this region is often referred to as a "tropical cyclone graveyard" by meteorologists.

Hurricane Helene (2018)

Storm Active: September 7-16

On September 6, an extremely large tropical wave entered the Atlantic basin from west Africa, to which it had brought torrential rains over the past few days. By the time it hit water, the system already possessed a clear spin, and only a lack of central convection lay between it and tropical cyclone designation. This was immediately remedied on September 7 as more concentrated thunderstorms developed near the center. That afternoon, it was designated Tropical Depression Eight, only a few hundred miles west of Senegal. The massive system consolidated fairly quickly for its size and strengthened into Tropical Storm Helene shortly after.

There was some Saharan dry air to the north of Helene, but convection still managed to wrap around the center on September 8 and the storm continued to intensify. That evening, the center passed well south of the Cabo Verde islands, bringing some rain due to its large size, but sparing them from worse impacts. The next day, Helene was upgraded to a hurricane as it moved west away from the islands and it closed off a very large eye that evening. The cyclone turned toward the west-northwest by September 10. The eye also became better defined and Helene intensified into a category 2 hurricane. The next day, Helene reached its peak intensity of 110 mph sustained winds and a minimum central pressure of 966 mb.

By this time, a weakness in the subtropical ridge to the north of Helene (caused by a low over the northeast Atlantic) allowed the system to turn northwest and then toward the north. As it gained latitude, the cyclone encountered lower water temperatures and a drier atmosphere. It weakened to a category 1 on September 12, and to a tropical storm the next day.

Helene began to appear less tropical as it accelerated northward since it became increasingly asymmetric. Nevertheless, it maintained its status as a strong tropical storm into September 14. Soon after, rain bands in its eastern semicircle began to sweep across the Azores Islands. The center of circulation passed just west of the islands on September 15 and veered northeastward. Helene picked up more forward speed and transitioned into an extratropical cyclone over the cold northeastern Atlantic on September 16. The system eventually brought some stormy conditions to Ireland and the UK a few days later.

Helene was a large system, and developed an unusually large eye when it intensified into a hurricane.

Though it did not affect any large landmasses, Helene did have impacts in both the Cabo Verde and Azores Islands.

Tropical Storm Gordon (2018)

Storm Active: September 3-8

During the final days of August, a tropical wave whose axis extended from the Caribbean south of Hispaniola northward to the adjacent Atlantic waters began to produce increased thunderstorm activity throughout the region. However, upper level winds were quite strong over the wave. This prevented further development for a few days as it moved toward the west-northwest. The system passed over the southern Bahamas on September 2 and its satellite presentation improved markedly, though it still lacked a surface circulation. Only on September 3 did Florida radar detect a well-defined surface low, prompting the naming of Tropical Storm Gordon. At the time of naming, Gordon's center was over southern Florida. It moved over the Gulf of Mexico shortly afterward but continued to bring rain to the southern half of the peninsula for the remainder of the day.

While the core intermittently showed signs of an eyewall forming on radar, the overall satellite presentation of Gordon was lackluster as it moved through the Gulf over the next day. The radius of tropical storm force winds remained very small and heavy rain did not extend much beyond it. Nevertheless, maximum winds at the center reached strong tropical storm intensity by September 4. The waters of the Gulf of Mexico were quite warm, but fortunately Gordon's forward speed remained fairly high due to consistent steering patterns, and it moved quickly northwest. Late in the day, the cyclone reached its peak intensity of 70 mph winds and a pressure of 997 mb just before making landfall along the Gulf coast near the border of Mississippi and Alabama. Mississippi was spared most of Gordon's flooding rain impacts since almost all rain was to the east of the center. Some hurricane force gusts were also reported during landfall.

The system quickly weakened inland and became a tropical depression on September 5. Its movement slowed considerably once over land and it gradually moved northward through the midwest over the following couple of days, bringing heavy rainfall to a wide swath of the central U.S. before being absorbed.

The above image shows Gordon just before landfall on the Gulf coast.

Gordon's slow movement after landfall contributed to flooding rains throughout the central U.S.

Hurricane Florence (2018)

Storm Active: August 31-September 17

On August 30, a vigorous tropical wave entered the Atlantic from the west African coastline. While the system was initially large and disorganized, its center became much better defined over the next couple of days. The low passed just south of the Cape Verde Islands on the 31st, bringing some heavy rain and winds. Around the same time, it was classified Tropical Depression Six. Ocean temperatures were only marginal for development, but wind shear was very low and the air surrounding the system quite humid (any Saharan dry air was well to the north). Because of this, the cyclone strengthened as it moved west-northwestward away from the islands, becoming Tropical Storm Florence early on September 1.

Some more intensification occurred that evening, but wind shear out of the southwest suddenly exposed the center of circulation on September 2 and the system weakened slightly. As Florence continued on its west-northwest heading over the open central Atlantic, sea surface temperatures began to warm beneath it. Overnight, the system developed an inner core and strengthened into a strong tropical storm. However, even as temperatures warmed, wind shear increased also and the satellite presentation became a bit ragged. Nevertheless, Florence held its own on the 3rd and approached hurricane strength when a central dense overcast appeared. In defiance of almost all models and forecasts, the system continued to intensify on September 4 and became a hurricane. It turned a bit toward the northwest that evening and an eye became apparent on satellite imagery. The next morning, the eye became better defined and cleared out further. Florence was then upgraded to a category 3 hurricane, the first major hurricane of the 2018 season.

That afternoon, the cyclone peaked as a category 4 hurricane with winds of 130 mph and a minimum pressure of 953 mb before wind shear out of the southwest finally began to take its toll. The southern eyewall thinned and then broke under the shear, the inner core became disrupted, and Florence lost major hurricane status on September 6. Rapid weakening continued throughout the day, and the center nearly became exposed from time to time overnight as the system weakened back to a tropical storm. Meanwhile, mid-level ridging to the north of Florence turned the shallower system back toward the west on September 7. The weakening trend halted that afternoon as shear began to abate and convection gradually worked its way back over the center. But while waters were warm and upper-level winds were more favorable, the circulation had ingested some dry air that it struggled to mix out through the day of September 8. Nevertheless, it approached hurricane strength once again by that evening.

The next day, deeper convection blossomed near the center and hints of an eye reappeared. Florence regained category 1 status that morning and began a process of rapid intensification. This process really accelerated when a symmetrical eye appearing late on September 9. By the afternoon on the 10th, the system was a dangerous category 4, surpassing its earlier peak intensity to reach a new peak of 140 mph winds and a central pressure of 939 mb. Meanwhile, a very strong subtropical ridge began building to its north and Florence turned west-northwest with a greater forward speed. Overnight, the core underwent an eyewall replacement as the small inner eyewall collapsed in favor of a broader outer one. This took some time to consolidate, leaving Florence with a lopsided appearance on infrared imagery. However, the new eyewall eventually closed off and the system maintained category 4 strength. Moreover, eyewall replacement cycles usually are accompanied by a broadening of the wind field; this held true for Florence. Its tropical storm force and hurricane force wind radii increased markedly by September 12.

By September 13, the maximum winds had decreased to category 2 strength, but the system had grown considerably. Its outer bands began to sweep across the coast of southeastern North Carolina that morning. Florence's speed slowed during the day and it stalled off the coastline. That evening, it turned toward the west and ultimately made landfall overnight as a category 1 hurricane. Even as the storm weakened, torrential rains continued to fall over much of coastal North Carolina and pushed into South Carolina on September 14. Florence became a tropical storm that day and the center crossed the border into South Carolina over land. As the circulation spun down, the core lost much of its strength, but the portion of the storm still over water to the northeast of the center was still dragging immense amounts of tropical moisture over coastal North Carolina on September 15. Along with the flooding rains came intermittent tornadoes reported in the northeast part of the circulation.

Overnight, Florence weakened to a tropical depression and finally began to pick up some speed inland toward the west and then north through Appalachia. By September 17, the system turned northeast under the influence of the mid-latitude westerlies and rains spread eastward into the mid-Atlantic, though nowhere near as severe as they had been in the Carolinas. The low pressure center of Florence became elongated later that day and the system finally transitioned to post-tropical near West Virginia. Soon, the remnants moved eastward over the Atlantic. The extratropical successor to Florence eventually spawned a new low in the subtropical Atlantic that would become Leslie. Even well after the storm had passed, river flooding continued for the Carolinas. Florence's devastating rainfall, totaling over 30 inches in parts of coastal North Carolina, made it among the costliest tropical cyclones ever recorded.

The above image shows Florence near peak intensity as a category 4 hurricane.

Florence's track was highly unusual. In a vast majority of instances, cyclones that traversed the Atlantic at the latitude that Florence did would recurve out to sea before hitting land. However, very strong subtropical ridges steered the storm into the Carolinas.

Tropical Storm Ernesto (2018)

Storm Active: August 15-18

On August 12, a low pressure area formed over the subtropical Atlantic well to the southeast off the coast of Nova Scotia. Over the following few days it moved generally toward the east and then southeast. In the meantime, very warm waters in the region allowed it to organize as atmospheric conditions improved. By August 15, the low's center had become well-defined, though the surface center was still situated under an upper-level low and the radius of maximum winds was rather broad. In light of these features, the system was classified Subtropical Depression Five that day.

The depression turned toward the north that day and strengthened into Subtropical Storm Ernesto. Marginal sea surface temperatures allowed a slight bit of intensification the next day and a transition to a fully tropical storm with convection closer to the center. At the same time, the storm began to feel the influence of the mid-latitude westerlies and accelerated northeast and then east-northeast. Ocean temperatures under the storm plummeted on August 17, but humid and unstable air in the region allowed Ernesto to maintain tropical cyclone status for somewhat longer than originally expected. Early on August 18, the system transitioned into a post-tropical storm west of Ireland. Nevertheless, it brought areas of heavy rain and gusty winds to northern Ireland and the United Kingdom as it merged with a front later that day. In both origin and track, Ernesto was very similar to its predecessor, Debby. In addition, it was the fourth system to become a subtropical storm in the 2018 season. This was the first such occurrence since 1969.

The above image shows Ernesto as a subtropical storm shortly after formation.

While Ernesto did not affect land as a subtropical or tropical cyclone, its remnants did impact the United Kingdom and Ireland.

Tropical Storm Debby (2018)

Storm Active: August 7-9

During the first few days of August, a non-tropical low meandered over the north central Atlantic. By the 4th, it was producing gale force winds, but had very little thunderstorm activity associated with it. Over the next couple days, it drifted southeastward, moving over water that was a tad warmer. The system again became stationary and then started to move back to the north, but by this time it acquired more significant convection. On August 7, the system was classified as Subtropical Storm Debby due to the spread of tropical storm force winds and outer banding from the center.

The storm slowed a bit overnight and turned toward the north-northeast on August 8. At the same time, the maximum winds increased somewhat and thunderstorms became more concentrated close to the center of circulation. As a result, Debby was reclassified as a tropical storm that morning. The cyclone also reached its peak intensity of 45 mph winds and a pressure of 1003 mb. Soon, however, the system began to weaken over the cold north Atlantic. Debby transitioned to a post-tropical storm during the afternoon of August 9 as it accelerated to the northeast, far from any land.

Debby was a small and short-lived cyclone that did not have any land impacts.

The above image shows Debby's track over the north Atlantic.

Hurricane Chris (2018)

Storm Active: July 6-12

During the first couple days of July, an disturbance formed in the subtropical Atlantic southeast of Bermuda. Over the next few days, it moved slowly northwestward and environmental conditions gradually improved for development. On July 5, the system acquired a weak low-pressure center. This became someone better defined that day, but thunderstorm activity remained quite limited. It increased on July 6, however, and the system was classified Tropical Depression Three well offshore of the Carolinas.

That night, it turned toward the north and became somewhat more organized over the warm waters. Surface pressure were still high, however, and the system's maximum winds increased only slowly. Meanwhile, steering currents collapsed and the depression moved very little on July 7. Most thunderstorm activity was displaced south and southeast of the center, keeping coastal North Carolina, which was not far to the northwest, dry. A reformation of the surface circulation to the south allowed the system to organize further and strengthen into Tropical Storm Chris by early on July 8. The next day saw gradual strengthening as the circulation tightened, but dry air intrusion prevented Chris from closing off an eyewall. By that evening, the system was on the verge of hurricane strength and finally began to move slowly toward the northeast. Though it began to move away from land, high surf continued to pound the coastline.

Since it had been stationary for days, Chris had caused cold waters to upwell underneath it (due to its strong winds). Though this decrease in temperature was mitigated somewhat by the steady flow of warm Gulf stream waters, it slowed the cyclone's intensification. However, once it started moving, the system rapidly intensified. Late on July 10, it reached its peak intensity as a category 2 hurricane with 105 mph winds and a pressure of 970 mb. As it accelerated northeast, it began to encounter cooler water, weaken, and become less symmetric. Soon, it weakened to a tropical storm and was quickly transitioning to an extratropical system. Chris became fully extratropical on July 12 as it raced northeast over cold north Atlantic waters. The post-tropical cyclone made landfall in southeastern Newfoundland that night, bringing wind gusts to near hurricane force and brief but heavy rains.

The above image shows Hurricane Chris strengthening off the U.S. east coast. Chris was the earliest second hurricane to develop in the Atlantic since 2005.

Chris did not affect land directly as a tropical cyclone, but made landfall in Newfoundland as a post-tropical cyclone.

Hurricane Beryl (2018)

Storm Active: July 5-8, 14-15

At the beginning of July, a tropical wave emerged off of the coast of Africa. This tropical wave was among the first of the season to develop significant convection over the central tropical Atlantic. Despite anomalously cool waters, conditions were still favorable enough in the deep tropics to support development. By July 4, the disturbance was quite well organized, with low shear in its environment and an evident circulation. Nevertheless, the low did not yet appear closed. The next day, organization increased further, and the system was classified as Tropical Depression Two. The depression was quite small and moving fairly quickly toward the west.

It is not uncommon for small cyclones to change rapidly in intensity, and the system strengthened quickly that evening and into July 6, becoming Tropical Storm Beryl just a few hours after formation. A minuscule pinhole eye appeared on satellite imagery and the maximum winds shot up to hurricane strength, making Beryl the first hurricane of the 2018 season by early on the 6th. The system strengthened a little bit more during that day, reaching a peak intensity of 80 mph winds and a pressure of 994 mb. Beryl turned a bit toward the west-northwest during the evening and into July 7. As it did so, it began to encounter increased wind shear. Quickly, convection was displaced toward the southeast and the center was exposed. As a result, Beryl began to quickly weaken and became a tropical storm. Convection flared up near the center from time to time over the following day but the low-level center all but disappeared as the cyclone accelerated west-northwest toward the Windward Islands. As shear continued to increase, Beryl quickly dissipated into a tropical wave.

Nevertheless, Beryl's remnants passed over the easternmost Caribbean islands on July 8, bringing heavy rains and strong winds out of the east. By the 9th, these rains had begun to move over Puerto Rico and the Virgin Islands. Overnight, the heavy rains moved over Hispaniola as the wave proceeded west-northwestward. The wave began to encounter more favorable conditions over the Bahamas, though the main impact to these areas was still locally heavy rain. After that, the disturbance turned northward and then northeastward, passing to the west of Bermuda.

Only on July 13 did the remnants of Beryl begin to show signs of reorganization, with a well-defined circulation developing. Despite marginal sea surface temperatures and atmospheric conditions, thunderstorm activity reappeared near the low-pressure center. On July 14, a full six days after dissipation, Beryl reformed. Though its windfield was concentrated near the center (typical for a tropical cyclone), the system lay under an upper-level trough. Therefore, it was deriving its energy in a manner uncharacteristic of a tropical cyclone. As a result, forecasters classified it as Subtropical Storm Beryl north of Bermuda.

The system slowed its forward motion and meandered somewhat over the next day. Vertical shear was increasing, but Beryl maintained enough convection in the southeastern quadrant to hang on to subtropical storm status. Even this was short-lived, however, and the system finally weakened into a remnant low late on July 15. This low approached Newfoundland before dissipating.

Beryl was one of the smallest hurricanes ever recorded; winds of hurricane force extended only 10 miles from the center. Note also the minuscule eye on satellite imagery.

A majority of Beryl's impacts occurred while the system was a wave moving through the Caribbean (triangle points).