Wednesday, October 5, 2016

Hurricane Nicole (2016)

Storm Active: October 4-18

During late September, a tropical wave was traversing the central Atlantic. Strong upper-level winds made it difficult for the system to organize, but by October 1, a low pressure center developed and the disturbance was producing strong winds. It moved northwest over the following few days and slowly organized as conditions became somewhat more favorable. By October 3, thunderstorm activity had become more concentrated. The next day, the system was producing winds to tropical storm force, and the circulation became better defined. Therefore, the system was designated Tropical Storm Nicole late in the morning on October 4.

It exhibited organized banding features and a well-defined circulation through the next day despite moderate shear. Meanwhile, the small system moved generally west-northwest into October 5. The cyclone continued to defy somewhat unfavorable atmospheric conditions and rapidly intensified over the following day, achieving hurricane status during the afternoon of October 6. An eye appeared on satellite imagery at the same time, and Nicole sped to an intensity of 105 mph winds and a pressure of 968 mb. The cyclone then stopped in its tracks and reversed course toward the south by October 7. Wind shear increased drastically and weakened Nicole as quickly as it had strengthened in addition to periodically exposing the center. By October 8, the system was again a fairly weak tropical storm, though vigorous convection bursts appeared intermittently throughout the day.

Nicole once again slowed to a standstill overnight and upper-level winds slowly relaxed. This allowed the system to recover some organization and initiate a slow strengthening trend. Later on October 9, Nicole finally assumed a more typical northward motion after meandering over the open Atlantic for several days. The next day, the system was again a strong tropical storm. However, the system still struggled with some dry air aloft even as it passed over very warm waters. It managed to develop a ragged eye feature during the morning of October 11, and intensification restarted. In fact, the system rapidly intensified into a hurricane that evening, and a category 2 storm by early on October 12. By this point, the cyclone was moving north-northwestward toward Bermuda. Later that day, the eye became quite large and symmetric and the system had outstanding outflow in all quadrants. These new increases in organization merited an upgrade to a major hurricane that evening and Nicole reached category 4 status briefly that night. Its peak intensity of 130 mph winds and a minimum pressure of 950 mb occurred as the system accelerated toward the north and tropical storm force winds began to engulf Bermuda.

Just after achieving peak intensity, the cyclone experienced a huge increase in wind shear, causing significant weakening to begin early on October 13. Nicole's center passed within 10 miles of Bermuda that morning with the cyclone still at category 3 strength, bringing hurricane force sustained winds to the island. By this time, the system was turning toward the northeast and gaining forward speed. Meanwhile, shear and decreasing ocean temperatures quickly weakened Nicole back to category 1 strength. The system acquired some extratropical characteristics the next day, but rather than transitioning fully, it became a sort of hybrid cyclone: the windfield and size of the system were typical of an extratropical system, but the inner core remained that of a tropical cyclone.

Late on October 14, Nicole briefly weakened to a tropical storm, but baroclinic processes reintensified the system the next day to a very powerful north Atlantic hurricane. It also turned toward the east on October 15 and slowed in forward speed. By the next morning, it had maximum winds of 85 mph and a pressure of 958 mb and was generating large ocean swells throughout the north Atlantic. Some weakening ensued the following day, but Nicole remained a hurricane through the morning of October 17. Diminishing ocean temperatures finally caught up to the system that night, purging the remaining tropical characteristics, and Nicole became post-tropical early on October 18. The cyclone remained extremely powerful for the next few days as it interacted with a frontal low and brought unusually strong winds to the southern coast of Greenland before being absorbed.

The above image shows hurricane Nicole at peak intensity shortly before impacting Bermuda. Since Matthew and Nicole both were category 4 hurricanes in October, the 2016 season was the first in recorded history to have two storms of at least category 4 strength in this month.

Nicole's meandering track brought it southward before doubling back toward Bermuda, stalling over the far northern Atlantic, and finally having impacts as far north as Greenland as an extratropical system.

Thursday, September 29, 2016

Hurricane Matthew (2016)

Storm Active: September 28-October 9

On September 22, a tropical wave exited in the African coast and moved rapidly westward across the Atlantic. For the next few days, the wave remained south of 10°N and embedded in the Intertropical Convergence Zone. Combined with the dry air over the east Atlantic, this factor precluded development initially. By the 26th, thunderstorm activity had increased and spiral bands had begun to appear on the north side of the disturbance. The system was still too far south to acquire spin, but it began to move west-northwest over the following day and acquired additional organization. By September 27, the wave was generating winds to near tropical storm force, but had not yet developed a closed circulation. Early on September 28, the system appeared on satellite imagery to be more organized, and aircraft reconnaissance confirmed the presence of a closed circulation later that day. Therefore, advisories were initiated on Tropical Storm Matthew. The aircraft also estimated that surface winds of 60 mph were already present, making the newly formed Matthew already a strong tropical storm.

At the time of formation, Matthew was passing through the Lesser Antilles and entering the Caribbean, bringing strong storms to the region. During the morning of September 29, moderate shear out of the southwest exposed the center briefly. However, high ocean temperatures and increasing humid air near the system allowed an inner core to quickly develop. By the middle of the afternoon, Matthew had strengthened to a hurricane. Meanwhile, the cyclone veered slightly south of west. Overnight, strengthening continued, bringing Matthew to category 2 status by the morning of September 30. Conditions began to deteriorate in the northernmost areas of Columbia later that morning. It is very unusual for tropical cyclones to affect South America, but Matthew's track was quite far south through the Caribbean. Around the same time, an eye appeared on satellite imagery and further rapid intensification took place. That afternoon, the system vaulted through category 3 and up to category 4 status. During the late evening, Matthew peaked as a category 5 hurricane with winds of 160 mph and a central pressure of 941 mb, making it the first category 5 hurricane in the Atlantic since Felix in 2007. Achieving this intensity at 13.3°N latitude, it was also the southernmost category 5 hurricane ever recorded in the Atlantic.

The forward speed of the system had slowed considerably at this point, although it was still moving west or just south of west. Early on October 1, the eye shrunk and the inner core became less organized, resulting in some weakening that day. This weakening was temporary, however, for after completing a small cyclonic loop that afternoon, Matthew regained strong category 4 strength and its new lowest pressure of 940 mb. The cyclone's motion remained slow and somewhat erratic through the following day, averaging to a general northwestward track during the day of October 2. Later that day, the outer rain bands of Matthew began to affect Jamaica and Haiti as it approached from the south. The system turned to the north and experienced slight weakening that night, but still maintained category 4 intensity. Matthew's structure did not change much the next day as it steadily approached the Greater Antilles. Extremely heavy rains began over Haiti on the 3rd and continued as the storm came closer and closer. Early on October 4, the center passed well to the east of Jamaica, though the island still experienced tropical storm conditions. Meanwhile, Matthew's pressure dropped to 934 mb, though the winds remained within category 4 intensity. Around 7:00 am EDT on October 4, Matthew made landfall in southwestern Haiti with maximum winds of 145 mph, the strongest hurricane to make landfall in the country in over 50 years.

Interaction with land began to slowly weaken the system, though the inner core remained largely intact. The cyclone emerged over water a few hours later and traversed the channel between Cuba and Haiti that day. It remained a category 4 with 140 mph winds when it made landfall near the eastern tip of Cuba at 8:00 pm EDT that evening. The cyclone stalled its northward motion slightly over land and weakened more substantially, becoming a category 3 storm early on October 5. By that time, it had again emerged over water and was entering the Bahamas. An amplifying ridge to the cyclone's east caused a northwest turn later that day. Meanwhile, Matthew began to recover from its land interactions that evening, with the pressure dropping and winds increasing as the eye passed through the Bahamas. Later on October 6, Matthew peaked as a category 4 once again. Rain bands had begun to affect Florida's east coast at this point and the cyclone continued to move closer to land, turning toward the north as it did so. Overnight, the center moved roughly parallel to the central and northern Florida coastline, with the outer eyewall bringing strong winds and heavy rains to the coastline from about 30 miles offshore.

Land interaction and increasing shear also started to weaken the storm as it moved northward. By the time it passed the coast of Georgia very early on October 8, the winds had diminished to category 2 strength. Matthew continued its turn and began to move northeast parallel to the U.S. coastline before finally crossing the shore late that morning as a category 1 hurricane in central South Carolina. Though the maximum winds had decreased by this point, very high levels of moisture in the atmosphere contributed to a huge rainfall event for the Carolina coasts, with over 10 inches of rain falling over a large swath of the region. In addition, the cyclone produced a large storm surge that inundated some low-lying areas. However, by this point, the hurricane was quickly acquiring extratropical characteristics, and transition was completed early on October 9. Though the system was moving eastward away from the coast, rains continued in the Outer Banks of North Carolina through the day before tapering off. The extratropical system was absorbed by a front the next day.

Hurricane Matthew was the first category 5 hurricane in the Atlantic in 9 years. The storm killed over 1000 people, a majority of whom lived in Haiti, making it the deadliest cyclone in the Atlantic since 2005. It also caused over five billion dollars in damages and was the costliest Atlantic hurricane since Hurricane Sandy of 2012. The above image shows the cyclone at peak intensity in the Caribbean Sea.

Matthew formed and strengthened unusually far south in the Caribbean before turning sharply northward and impacting the Greater Antilles, the Bahamas, and the U.S. east coast.

Tuesday, September 20, 2016

Tropical Storm Lisa (2016)

Storm Active: September 19-24

On September 16, a tropical wave moved off of Africa into quite favorable conditions in the eastern Atlantic. As a result, an area of low pressure developed almost immediately and an impressively broad circulation developed. After initially having some trouble consolidating, the circulation became well-defined on September 19 and the system was classified Tropical Depression Thirteen. Shortly after formation, the depression took a west-northwest turn toward a weakness in the ridge to its north. Steady organization followed over the next 24 hours as the system strengthened into Tropical Storm Lisa during the morning of September 20 and then experienced more strengthening through that evening.

Due to the presence of an upper-level low pressure system located to the northwest of Lisa, shear out of the west and southwest began to increase dramatically on September 21, gradually exposing the center of circulation as convection retreated to the east. Lisa held its own, however, continuing to produce very deep convective bursts. It even rebounded from a momentary weakening that day by strengthening to its peak intensity of 50 mph winds and a pressure of 999 mb during the morning of September 22. There was evidence by this point that the circulation was becoming elongated in response to the continued shear. Meanwhile, thunderstorm activity began to wane and Lisa weakened through the rest of the day and overnight.

The storm experienced once last resurgence of thunderstorms during the morning of the 24th and in fact was upgraded back to tropical storm status as a result. However, this was only a temporary reprieve. By that afternoon, the circulation was entirely bare. Lisa was downgraded to a tropical depression that afternoon and a remnant low that night. The circulation produced shower activity for an additional few days before dissipation.

The image shows a disorganized Lisa over the eastern Atlantic.

A break in the ridge to Lisa's north allowed it to veer north quite far east and encounter hostile atmospheric conditions quite quickly.

Thursday, September 15, 2016

Tropical Storm Karl (2016)

Storm Active: September 14-25

On September 12, a tropical wave near the African coastline began to show signs of development. Beginning the next day, gusty winds and locally heavy rain began to affect the Cape Verde Islands as the disturbance moved west-northwest toward them. The system acquired a surface circulation fairly rapidly and was classified Tropical Depression Twelve on September 14, while still over the islands. Moderate wind shear out of the west kept the center exposed and prevented strengthening over the next day. Late on September 15, however, organization markedly increased and the depression intensified into Tropical Storm Karl.

The next day, thunderstorm activity was pushed a bit farther away from the center by the wind shear, and Karl lost some organization. Additionally, the system took a turn to slightly south of due west by the morning of the 17th. Slight weakening followed, though Karl remained essentially steady state through September 18. The system's direction did change toward the west-northwest, and Karl began to gain latitude. Late on September 19, it appeared that the system was finally starting to organize as shear diminished, but thunderstorm activity collapsed into disorder again the next morning. Upper-level winds had not abated as anticipated, and the Karl in fact weakened to a tropical depression late on September 20th.

The long-awaited relaxation of shear commenced the following day, and the overall structure of Karl became much more symmetric, with banding features and deep convection on all sides of the circulation. This large-scale improvement was unusually not accompanied by any development of the inner core. Rather, it remained broad, rather like a pre-tropical system. As a result, Karl remained a tropical depression through the morning of September 22, still moving northwestward over the open Atlantic. Later that day, the cyclone finally began to strengthen, regaining tropical storm strength that evening and continuing to intensify through the morning of September 23 as outflow drastically improved. The system began to round the edge of the subtropical ridge that day and turned toward the north.

Conditions worsened in Bermuda throughout the day as Karl approached, eventually escalating to tropical storm force winds and heavy rains overnight. The center turned to the northeast just short of Bermuda early on September 24 and the system began to quickly accelerate away from the island. Wind shear was high across the system, but as it was beginning to undergo extratropical transition, there was some increase in intensity that day, bringing Karl to its peak of 70 mph winds and a pressure of 990 mb that night. By the morning of September 25, the cyclone was speeding northeast at almost 50 mph and was declared extratropical.

The above image shows Karl just after passing Bermuda.

Despite existing as a tropical cyclone for 11 days, Karl was never able to intensify into a hurricane.

Wednesday, September 14, 2016

Tropical Storm Julia (2016)

Storm Active: September 13-18

On September 8, a tropical wave located east of the Lesser Antilles began to exhibit some signs of organization. However, atmospheric conditions were rather hostile, so the system moved west-northwest and then northwest for several days without significant change. On September 11 and 12, the disturbance brought some storms to the Bahamas as it passed through. Surface pressures remained high, so not development occurred during that time. That night, the circulation center of the low moved over the Florida peninsula. Despite this, the warm waters just to the east fueled a huge increase in convection just offshore and caused the system to strengthen. Late on September 13, the low was upgraded to Tropical Storm Julia even while the center was just inland over northeastern Florida. Julia was the first Atlantic storm to form over land since 1988.

After moving northward overnight and crossing inland into Georgia, the center reformed farther east on the 14th and moved over water. Though land interaction lessened, wind shear increased out of the west. This made it difficult for Julia to develop thunderstorm activity over the center and the system weakened to a tropical depression by the morning of September 15. Now moving slowly eastward, Julia put some distance between itself and the coast, ending significant rainfall over the Carolinas and Georgia and averting a potential flooding event. That night, new convective bursts including gale force winds indicated that the system was once again a tropical storm.

Over the next day, the forward motion of Julia slowed to a standstill and it lost organization as hostile conditions continued. As a result, it was again downgraded to a depression by the morning of September 17. The cyclone maintained no persistent convective features that day, but intermittent bursts were enough to maintain the cyclone as tropical. In the meantime, the center of circulation adopted a slow northwestward drift. Soon, however, dry air finally overwhelmed the system, and it was downgraded to a remnant low the evening of September 18. The low continued northwestward slowly until it merged with a front near the coast of North Carolina.

The above image shows Tropical Storm Julia shortly after formation over Florida. Most convection associated with the system remained offshore to the east.

Julia meandered near the U.S. southeast for several days before wind shear and dry air destroyed the system.

Monday, September 12, 2016

Tropical Storm Ian (2016)

Storm Active: September 12-16

Near the end of September's first week, a tropical wave developed over the central Atlantic. Soon, a low pressure center developed along the southern portion of the wave and began to produce a large area of showers and thunderstorms. Despite conditions being very favorable for development, the system organized only slowly as it moved northwestward. By late on September 11, the low was producing gale-force winds. However, it did not yet possess a well-defined center of circulation. Despite the fact that upper-level winds had increased somewhat, the low managed to organize into Tropical Storm Ian during the morning of September 12.

Convection remained confined to the northeast of the center through the remainder of that day. Meanwhile, the system turned toward the north-northwest well to the east of the Lesser Antilles. The area of tropical storm force winds did experience an expansion that evening, and maximum winds increased somewhat, but Ian's structure did not meaningfully change until the afternoon of the 13th. At that time, convection managed to cover the center for the first time. However, the cyclone began to lose tropical characteristics shortly afterward, with the circulation becoming broader and losing concentrated thunderstorm activity near the center. By the morning of September 15, it was accelerating north-northeast over the open Atlantic. Ian actually appeared more tropical later that day than it had for a couple days, with deep convection reappearing close to the circulation center. However, it was racing toward the north Atlantic by this time, briefly achieving a forward speed of over 50 mph that night. At the same time, it experienced some intensification, reaching 60 mph winds and a pressure of 994 mb by the morning of September 16. The cyclone in fact continued strengthening as it became extratropical that afternoon. It merged with another strong low over the north Atlantic shortly afterward.

The image above shows Tropical Storm Ian shortly after formation.

Ian did not affect any landmasses over its short lifetime as a tropical cyclone.

Monday, August 29, 2016

Hurricane Hermine (2016)

Storm Active: August 28-September 3

On August 18, a tropical wave just southwest of the Cape Verde Islands began to display scattered shower activity. The system remained rather broad and disorganized during its trek westward across the Atlantic for most of the following week. Throughout much of this period, the wave and associated low were little more than an large swirl of sparse clouds with limited convection farther south. This was due to the influence of the Saharan air mass to the north. Organization increased some around the 22nd and 23rd as the low passed through the Lesser Antilles, but a well-defined circulation did not yet develop. In fact, organization decreased markedly over the following several days, as the convection became scattered across many of the islands of the Caribbean away from the center. It was not until the system passed just south of the Florida Keys on August 28 that it finally acquired the status of Tropical Depression Nine.

The location of the center of circulation remained difficult to spot on satellite imagery through the next day, but convection increased overall, particularly to the south of the center. This caused heavy rains for much of western Cuba. Organization increased markedly on August 30 and the subsequent overnight period: a large area of very deep convection developed over the southeastern Gulf of Mexico surrounding the center and the central pressure dropped appreciably. This did not immediately correspond to an increase in maximum winds, but aircraft data collected the afternoon of August 31 indicated that the system had finally strengthened into Tropical Storm Hermine.

By this time, the cyclone had assumed a track toward the north-northeast due to the influence of a trough over the southeastern United States. At the same time, atmospheric conditions improved, allowing Hermine to take advantage of the very warm Gulf waters and intensify quickly. That evening, the storm developed more organized banding features, with a huge band extended from northwest to southeast of the center. Shortly afterward, this band began to affect the Florida panhandle. By the morning of September 1, heavy rain was moving across western Florida as far south as Tampa. An eyewall appeared later that morning and completed its circumnavigation of the center that afternoon. Hermine became a category 1 hurricane soon after. A few hours later, the cyclone reached its peak intensity of 80 mph winds and a central pressure of 984 mb and made landfall in the Florida panhandle, causing storm surges of several feet, strong winds, and over 5 inches of rain for many areas.

Hermine weakened to a tropical storm overnight and move inland over Georgia by the morning of September 2. The cyclone traversed South Carolina that afternoon and entered North Carolina that evening. All the while, it weakened and gradually lost tropical characteristics. This did not prevent it from causing flooding rains from the Carolinas north to the Delmarva peninsula by the morning of September 3. Around this time, Hermine became post-tropical and moved east-northeast back over water. There it reintensified some and developed winds near hurricane force. While storm surge remained a threat to the coast, the system moved farther away from land over the next day, lessening direct impacts. Early on September 5, Hermine changed course, moving first slowly northward, and then toward the west-northwest by the afternoon. Though it remained post-tropical, the system generated some shallow convection to the north and west of the center, bringing continued shower activity to coastal New England. The circulation began to spin down on the 6th, and while it moved a little closer to the coast, impacts diminished. By September 7, the weakening cyclone had switched direction and was moving generally east-northeast. It dissipated shortly after.

The above image shows Hermine shortly after it became a hurricane.

Hermine continued to affect the U.S. east coast even after transitioning to a post-tropical cyclone (post-tropical track points are indicated by triangles).

Sunday, August 28, 2016

Tropical Depression Eight (2016)

Storm Active: August 28-31

On August 26, an area of showers and thunderstorms developed in association with a low pressure system just south of Bermuda that had originated from a stalled frontal boundary. While the atmosphere was fairly dry, organization increased over the next day as the low moved toward the west-northwest. By the evening of August 27, the system had developed a roughly circular area of convection with the center of circulation on the eastern edge. The next morning, it was well-defined enough to be classified Tropical Depression Eight. Over the next day, shower activity blossomed only intermittently, leaving the circulation bare a majority of the time. Thus the system remained a tropical depression into August 29 as it turned toward the northwest. Its forward speed also decreased as it moved toward a break in the subtropical ridge to its north. As a result, it stalled off the coast, missing the Outer Banks of North Carolina by less than 100 miles. As a result, scattered showers and gusty winds affected portions of eastern North Carolina on August 30.

Later that day, Eight began to move slowly northeast away from the U.S. east coast. At the same time, the depression lost organization as it began to interact with a frontal boundary just off of the U.S. east coast. Convection became well displaced from the remaining circulation, and the system opened up into a trough early on August 31.

The above image shows Tropical Depression Eight near the coast of the Carolinas.

Tropical Depression Eight faced marginal conditions at best for development throughout its short lifetime.

Monday, August 22, 2016

Hurricane Gaston (2016)

Storm Active: August 22-September 3

During mid-August, a vigorous disturbance developed well inland over the continent of Africa. The potential development of this system once it emerged into the Atlantic was identified by August 17, three days before it encountered water. By the time it had moved over the ocean on August 20, a small area of thunderstorm activity persisted near its circulation center. Organization continued over the next few days and Tropical Depression Seven formed over the eastern Atlantic during the afternoon of August 22. Initially, conditions were favorable for development as the cyclone moved westward, and it quickly strengthened into Tropical Storm Gaston. The one inhibiting factor for rapid intensification over the following day was the Saharan dry air mass located to the north. Some of this air entered the circulation on the 23rd, forming a large eye-like structure near the center of circulation. However, Gaston managed to develop a central dense overcast shortly thereafter and became a strong tropical storm. Meanwhile, the system took a turn toward the northwest. As it was nearing hurricane strength on August 24, wind shear increased, slowing development. Nevertheless, the system overcame increasing upper-level winds out of the southwest to achieve hurricane status early on August 25, becoming the third hurricane of the 2016 Atlantic season.

However, the deteriorating atmospheric conditions soon disrupted Gaston's circulation, weakening it back to a tropical storm later that day. Squeezed between a upper-level low (the source of the shear) and a ridge to its north, the system moved rather quickly toward the northwest for the remainder of that day and gradually weakened. The next day, shear abated and the tropical storm began to reorganize. As a result, strengthening began once again by the morning of August 27. While Gaston was still moving northwestward, its forward speed slowed considerably that day. An eye feature developed overnight, and steady strengthening continued through the morning of the 28th, bringing the cyclone to category 2 hurricane status. That evening, the system slowed to a standstill and became the first major hurricane of the season. Just afterward, it reached an intensity of 120 mph winds and a pressure of 957 mb.

By August 29, Gaston had gained enough latitude to be affected by the mid-latitude westerlies and began a turn toward the northeast. The cyclone came off its peak intensity that day as the eye clouded over temporarily. However, once the eyewall replacement cycle was complete that night, a very large, symmetrical eye appeared on satellite imagery. Therefore, Gaston strengthened once again during the day of August 30 and regained major hurricane status that night, matching its peak winds of 120 mph and beating its former minimum pressure by achieving a mark of 956 mb. However, cooler water and increasing shear finally began to take their toll the next day and a steadier weakening began as Gaston accelerated off to the east-northeast. By the evening of August 31, the winds had decreased to category 1 intensity and the convection had become asymmetrical. This is typical of system beginning to lose tropical characteristics, and the trend continued into September 1, by which time only the northern side remained of the eyewall.

The remaining thunderstorm activity became decoupled from the center that evening as the cyclone took another turn toward due east. On September 2, Gaston weakened to a tropical storm and moved into the Azores. Later that day, however, most of the cloud tops disappeared, leaving a bare circulation. As a result, the system became post-tropical early on September 3. It was absorbed by a large extratropical system about one day later.

Hurricane Gaston achieved its second peak intensity on August 30, at which time its structure included a very large eye (above).

Gaston was the second tropical cyclone of the 2016 season to affect the Azores, after Hurricane Alex in January. For two such storms to affect the Azores in a season is highly unusual.

Wednesday, August 17, 2016

Tropical Storm Fiona (2016)

Storm Active: August 16-23

On August 14, a tropical wave formed near the western coast of Africa and began to produce a large region of disorganized thunderstorm activity. Over the next couple days, the system moved generally west-northwestward and developed a small but vigorous circulation. Late on the 16th, the system was designated Tropical Depression Six. Water temperatures were warm in the region and wind shear was abating. However, as with many tropical cyclones in the central Atlantic, the depression had to contend with low humidity values in the surrounding air that constantly threatened to overwhelm the small system.

On August 17, a small concentrated burst of convection replaced the larger but less powerful banding features, resulting in the cyclone's upgrade to Tropical Storm Fiona. Thunderstorm activity waxed and waned over the next day following the usual cycle by which convection preferentially forms at certain times of day due to solar heating of the ocean and atmosphere. Overall, Fiona's intensity remained virtually unchanged on August 18. Meanwhile, the cyclone moved generally northwest in towards a gap between high pressure systems centered in the east Atlantic and near Bermuda. Wind shear increased somewhat on August 19 but water temperatures continued to climb as Fiona traversed anomalously hot waters in the central Atlantic. As a result, bursts of convection continued to form. Fiona fluctuated in intensity a bit but this state of affairs remained mostly unchanged through the day on August 20. Overnight, the circulation center became exposed again, and the cyclone weakened to a tropical depression. Fiona struggled more to develop a convective canopy on the 21st, but it held its own enough to remain a depression through the day.

Over the following two days, the system continued to wane, with the circulation becoming elongated by August 23. This, coupled with a lack of persistent convection, prompted its downgrade to a remnant low that morning. The low continued west-northwestward for another few days before it dissipated over the western Atlantic.

Tropical Storm Fiona struggled with dry air for most of its lifetime.

Fiona did not approach land at any time during its trek through the central Atlantic.