Tuesday, August 31, 2010

Tropical Storm Fiona (2010)

Storm Active: August 30-September 3
On August 26, a strong tropical wave emerged off the coast of Africa, adopting the same general track of Danielle and Earl before it. By later that same day, a low pressure center became embedded in the wave. Although the outflow and circulation of the system was very organized from the beginning, convection remained minimal and a tropical depression didn't form during the next few days. On August 28, a burst of convection appeared at the center, but it ebbed away over the next day. By August 30, the system was producing tropical storm force winds, and a center was found, causing the low to be promoted to Tropical Storm Fiona, with no intermediate tropical depression stage.

Its initial intensity was 40 mph winds and a pressure of 1007 mb. Fiona sped off to the west and westnorthwest over the next day, and tropical storm watches were issued for some of the Northern Leeward Islands in preparation for possible tropical storm conditions in areas that were still recovering from Hurricane Earl. Fiona's motion was at least 20 mph until September 1, when the presence of Earl to its east slowed its motion. The outflow of Earl and Fiona kept a certain distance between the two, and Fiona actually became more organized as it slowed down, unexpectedly strengthening into a strong tropical storm by the morning of September 1, with winds of 60 mph. However, later on September 1, Fiona peaked at 60 mph and a pressure of 997 mb, before losing most of its cloud cover and weakening. Meanwhile, it turned to the northwest and sped up again through the morning of September 2. Fiona recovered some convection during the day, but intense shear exposed Fiona's circulation, and as it turned north, it continued to weaken. As Fiona struggled north-northeast, its pressure rose further, and it weakened to a tropical depression and then a remnant low late on September 3, before even reaching Bermuda.

The only effects of Fiona were some showers and gusty winds in the Northern Leeward Islands and Bermuda.

Fiona at peak intensity on September 1, despite the exposure of its circulation.

Track of Fiona, notable for coinciding almost exactly with that of Tropical Storm Colin earlier that year.

Thursday, August 26, 2010

Hurricane Earl (2010)

Storm Active: August 25-September 4
On August 23, a strong tropical wave emerged off of Africa and immediately began to show signs of organization. The wave developed a low pressure center on August 24, and during that day, brought rain and gusty winds to the Cape Verde Islands. However, the system did not possess a closed circulation until August 25, and was then declared Tropical Depression Seven. Upon formation, Seven was already on the verge of tropical storm intensity and in another six hours, during the afternoon on August 25, the system became Tropical Storm Earl.

Overnight, the outflow of the system grew very organized, suggesting strengthening, but the location of the center itself was a moving target, reforming every few hours in a slightly different location relative to the convection. The center became more defined with a burst of convection during the evening of August 26, but the system did not undergo significant intensification overnight. Earl persisted westward during the day of August 27, and tropical storm watches were issued for portions of the northern Leeward islands as a result. Meanwhile, Earl began to strengthen, reaching strong tropical storm intensity by August 28. Despite an early turn north on the models, Earl continued west much longer than expected, and continued strengthening. Earl attained hurricane strength on August 29, and hurricane watches and warnings were issued for parts of the Northern Leeward Islands.

Finally, Earl turned westnorthwest later that day, but the outer bands of Earl began to sweep across the northeasternmost islands of the Caribbean bringing heavy rains and wind, with conditions getting progressively worse into the evening hours. By 8:00 pm EDT that night, tropical storm force surface winds covered the northern Leeward Islands, and hurricane force sustained winds also brushed these areas causing intense storm surge and flooding. Meanwhile, Earl continued to gain strength and rapidly became a Category 2 very late on August 29 and was on the verge of major hurricane strength by the morning of August 30. An eye appeared in Earl during the day as it strengthened rapidly, becoming a major hurricane quickly and then a Category 4 as it passed north of the U.S. Virgin Islands and Puerto Rico and caused tropical storm force winds and rain throughout the regions. Earl's pressure continued to drop, and by August 31, Earl had reached an amazing intensity of 135 mph winds and a 931 mb pressure. It still maintained a general westnorthwest motion, and the eye clouded over somewhat as Earl went through the Eye Replacement Cycle. The pressure rose as the cycle progressed, and Earl turned northwest, passing east of the Bahamas. But Earl maintained a Category 4 intensity until September 1, when it encountered some more significant shear and weakened to a Category 3 hurricane. Earl slowly turned to the north-northwest and recovered an eye, becoming more organized during the afternoon of September 1, and it restrengthened into a Category 4 hurricane. It surpassed its previous peak in intensity and reached its primary peak of 145 mph winds and a pressure of 928 mb early on September 2!

The storm continued to approach the Outer Banks of North Carolina during the day. By that evening, rainbands and tropical storm force winds swept over Cape Hattaras and the surrounding areas, as Earl turned north-northeast. However, hurricane force winds stayed offshore. As Earl approached, the eye clouded over again and Earl began steadily weakening, to a Category 3, and then a Category 2 by the time it passed by Cape Hattaras early on September 3. The weakening continued, and Earl was a tropical storm by the time it brushed passed Cape Cod overnight, bringing tropical storm force winds and rain to that area as well. By September 4, conditions were deteriorating in Nova Scotia. During the day, Earl made landfall in Nova Scotia and then Prince Edward Island as a powerful tropical storm, before entering the Gulf of St. Lawrence and finally becoming extratropical late on September 4 just off the coast of northeast Quebec. In total, Earl caused $150 million in damages and 3 fatalities over the areas it affected.

Earl nearing its peak intensity east of the Bahamas on September 1.

Track of Earl.

Sunday, August 22, 2010

Hurricane Danielle (2010)

Storm Active: August 21-30
On August 19, a broad area of low pressure formed just of the coast of Africa and quickly developed deep convection due to its proximity to the Intertropical Convergence Zone. Over the next day, the system developed two centers along the trough, one on the eastern side, toward Africa, and one on the western side. The one on the western side was 1008 mb, as opposed to the eastern's 1011 mb, and the former soon gained dominance as the other dissipated. During the day of August 20, the system remained disorganized. However, during the afternoon on August 21, a closed circulation formed, and a very apparent spin appeared on satellite images, and the disturbance was classified Tropical Depression Six that day with 30 mph winds and a pressure of 1008 mb. Six strengthened as it moved westnorthwest, and a burst of convection near the center merited an upgrade to Tropical Storm Danielle during the afternoon of August 22.

Favorable conditions with warm water and minimal wind shear allowed Danielle to strengthen significantly through the night and into August 23. By the afternoon of that day, Danielle reached hurricane strength and was still rapidly intensifying. Also, contrary to previous models, Danielle still continued on a generally westnorthwestward track overnight and into the next day. During the early morning of August 24, Danielle reached Category 2 hurricane strength. However, a dry air mass embedded itself in the system during the afternoon, briefly exposing the center! This caused Danielle to weaken to a tropical storm by the evening, but already it had recovered and started to regain strength. By early on August 25, Danielle's movement slowly was shifting to the northwest, although it was still westnorthwest for much of the morning.

The system was also a hurricane again by this time and gaining intensity. Danielle maintained an intensity of 85 mph winds and a pressure of 982 mb through the day, and turned northwest during the evening. Also, an eye feature began to develop during the night, albeit an asymmetrical one, as Danielle once again became a Category 2 hurricane. The eye had been clouded over due to the Eye Replacement Cycle, but Danielle still gained intensity into August 26. Danielle redeveloped a well-formed eye during the day, and its movement to the northwest slowed as a trough interfered with its motion. Danielle continued to strengthen, becoming the first major hurricane of the 2010 season at 2 am EDT on August 27, and became a Category 4 just three hours later with an amazing intensity of 135 mph winds and a minimum central pressure of 946 mb. Later that day, Danielle achieved its peak intensity of 135 mph winds and a central pressure of 942 mb.

After that, Danielle began to be exposed to some wind shear and cooler waters, resulting in some weakening. Danielle lost its major hurricane status early on August 28, and continued its downward trend during that day as it turned to the north. During the day of August 28, Danielle, despite being over 1000 miles from the east coast, influenced the surf along the coastline, and created 3-6 foot waves and rip currents, killing one person in Florida. However, a trough moving off the east coast picked up Danielle and began to steer it to the east. That evening, Danielle's circulation broadened and became asymmetrical, marking the beginning of its extratropical transition. This transition continued into August 29, as the cyclone accelerated northeast and weakened to a Category 1 hurricane. By August 30, it was clear that Danielle was nearly extratropical and barely holding on to minimal hurricane strength, but it somehow stayed tropical through the day and turned more eastward, weakening to a tropical storm. However, by 11:00 pm EDT on August 30, Danielle had become fully extratropical and the last advisory was issued.

Danielle's remnants became embedded in a frontal boundary the next day, and it dissipated soon after as it sped off to the east. No damage and 1 indirect death occurred from Danielle.

Danielle near peak intensity over the open waters of the Atlantic.

Track of Danielle.

Wednesday, August 11, 2010

Tropical Depression Five (2010)

Storm Active: August 10-11
On August 8, a stationary frontal boundary off the east coast of the United States developed a low pressure system at its southern end. The force of high pressure systems to the west pushed the low south, where it encountered the typical west to east motions of the lower latitudes, and tracked over Florida on August 9, emerging over the Gulf of Mexico on August 10 as a 1010 mb low. The pressure continued to drop, and the circulation became organized enough to be declared Tropical Depression Five at its peak intensity of 35 mph winds and a pressure of 1007 mb. However, the convection associated with the system never attained definition with respect to the center, and the low weakened as it moved northwestward. The low dissipated before even reaching the Gulf coast on August 11. The broad area of low pressure associated with the dissipated Tropical Depression Five combined with a stationary front inland over the Gulf states in August 13. The system once again tracked southeastward, and approached the Gulf, intensifying as it went. As the low deepened, it became detached from the front, and by early on August 16, the system was a powerful 1010 mb low entering the Gulf with a fairly impressive clump of convection. However, no closed circulation formed, and the low made landfall once again in Louisiana without achieving tropical characteristics. The low moved north and dissipated.

Five in the Gulf of Mexico.

Track of Five.

Monday, August 2, 2010

Tropical Storm Colin (2010)

Storm Active: August 2-8
On July 29, a low pressure system formed in the southeast Atlantic and slowly drifted westward. The low became associated with a large area of showers and thunderstorms, but the system remained disorganized. A tropical wave accompanied the low as it drifted westward, but the wave disengaged from the circulation, and convection decreased. However, another tropical wave, moving off of Africa combined with the low during the day of July 31, and the systems had totally merged by August 1. However, this time convection persisted within the system and it organized. A flare up of convection that defined the system's center marked the formation of a closed circulation and the system was declared Tropical Depression Four on August 2. Tropical Depression Four's initial movement was swift, to west at 17 mph, due to the steering force of a subtropical ridge to its north. Overnight, Four became more organized, and it was upgraded to Tropical Storm Colin, with 40 mph winds and a pressure of 1006 mb, during the morning of August 3.

Colin accelerated to the west at an even greater speed, reaching a velocity of nearly 25 mph during the day on August 3. Then, the low pressure associated with the system became open, and it degenerated into a remnant low. However, cloud cover persisted within the system, and a new surface low pressure center became evident late on August 4. The system continued to organize, and was redesignated Tropical Storm Colin on August 5. Colin moved northwest and slowed in movement as it encountered a high pressure system, and began to turn east, as with most cyclones in the region. It briefly attained an intensity of 60 mph winds and a pressure of 1005 mb before the circulation became widely separated from the cloud cover again and Colin weakened to a weak tropical storm (45 mph winds) by August 6. Colin became nearly stationary on August 7, and weakened further, barely a tropical storm by the time it resumed movement to the northnortheast later that day. As Colin approached Bermuda, it weakened into a tropical depression, and brought needed rain to the island. Soon after passing west of Bermuda on August 8, Colin lost its circulation and dissipated.

Tropical Storm Colin shortly after reforming on August 5. The circulation, although more organized than before, is clearly exposed.

Track of Colin.