Category Archives: Atlantic, Caribbean, and Gulf of Mexico

Atlantic TCs

Rapidly Intensifying Tropical Storm Fred Threatens Cape Verde Islands

An area of low pressure organized quickly after it moved off the coast of West Africa and the National Hurricane Center designated it as Tropical Storm Fred.  At 2:00 p.m. EDT on Sunday the center of Tropical Storm Fred was located at latitude 14.1°N and longitude 20.7°W which put it about 195 miles (315 km) east-southeast of Praia in the Cape Verde Islands.  Fred was moving toward the northwest at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 1000 mb.  A Hurricane Warning has been issued for the Cape Verde Islands.

Tropical Storm Fred was a well organized low pressure system when it moved over the eastern Atlantic Ocean from West Africa.  The input of energy from the ocean enhanced the existing thunderstorms and the low pressure system quickly reached the intensity necessary to be classified as a tropical storm.  The circulation continued to organize further on Sunday.  A primary rainband has wrapped almost entirely around the center of circulation.  A small eye and an eyewall may be forming and other spiral bands of thunderstorms are developing.  The thunderstorms are generating upper level divergence which is pumping out mass.  Fred is moving over water where the Sea Surface Temperatures (SSTs) are near 27°C to 28°C.  The winds in the upper levels are relatively light and there is not much vertical wind shear.  The favorable environmental conditions are allowing Fred to intensify rapidly and it could become a hurricane tonight.  As Fred moves farther toward the northwest, it will start to move over cooler SSTs and into a region where there is more vertical wind shear.  As a result, Fred is likely to weaken back to tropical storm intensity later this week.

There is a weaker area in the subtropical ridge over the Atlantic Ocean and Fred is moving northwest toward that area.  The ridge is expected to strengthen during the week and as it strengthens it will cause Fred to move more toward the west.  On its anticipated track Fred will reach the Cape Verde Islands in about 12 hours.  It could bring strong winds and heavy rain when it move across those islands.

Tropical Storm Erika Bringing Heavy Rain to Hispaniola

Tropical Storm Erika is moving across Hispaniola and it is bringing heavy rain to parts of that island.  At 5:00 p.m. EDT the center of Tropical Storm Erika was located at latitude 17.9°N and longitude 71.2°W which put it about 95 miles (155 km) west-southwest of Santo Domingo, Dominican Republic and about 745 miles (1200 km) southeast of Miami, Florida.  Erika was moving toward the west at 21 m.p.h. (33 km/h).  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 1009 mb.  Tropical Storm Warnings have been issued for the southeastern Bahamas, the Turks and Caicos, for the Dominican Republic, Haiti, for the Central Bahamas including Cat Island, the Exumas, Long Island, Rum Cay and San Salvador.  Tropical Storm Watches have been issued for the northwestern Bahamas including the Abacos, Andros Island, Berry Island, Bimini, Eleuthera, Grand Bahama Island and New Providence, the Cuban provinces of Ciego de Avila, Camaguey, Las Tunas, Holguin and Guantanamo.

The circulation around Tropical Storm Erika is even less well organized today.  At times a small cyclonic rotation appeared on visible satellite images, while at other times Erika looked a lot like a very strong tropical wave.  Vertical wind shear caused by an upper level trough over the western Caribbean Sea has prevented thunderstorms from forming near the core of the circulation.  The lower part of the circulation will be significantly disrupted by the mountains of Hispaniola, but the middle portion may make it across the island.  If the middle level circulation is disrupted as well, then Erika will degenerate into a disorganized area of thunderstorms.  If the middle level circulation is still intact when it emerges west of Hispaniola, then it is possible that momentum could be transferred to the surface and a new low level center spun up.  Erika would most likely be a tropical depression at most at that time.  The water north of Cuba is very warm and if Erika still exists, it could intensify somewhat as it moves toward Florida.

The winds in the lower levels continued to push Erika toward the west-northwest on Friday and that general motion is likely continue for the next 12 to 12 hours.  Erika is getting closer to the western end of the subtropical high and it could turn more toward the north during the weekend.  On its anticipated track Erika or its remnants could be approaching the Florida Keys on Sunday afternoon.  At this time it is almost impossible to know how strong it will be at that time.  If Erika does start to reorganize when it gets west of Hispaniola, watches and/or warnings could be issued for parts of Florida.

Erika Bringing Heavy Rain to the Northeastern Caribbean

Although it is not very well organized, Tropical Storm Erika brought heavy rains to parts of the northeastern Caribbean Sea on Thursday and it caused flooding on Dominica.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Erika was located at latitude 16.6°N and longitude 65.3°W which put it about 135 miles (215 km) south-southeast of San Juan, Puerto Rico and about 1145 miles (1850 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 17 m.p.h. (28 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1008 mb.  Tropical Storm Warnings have been issued for Puerto Rico, Vieques, Culebra, the U.S. Virgin Islands, the British Virgin Islands, the southeastern Bahamas, the Turks and Caicos, the coast of the Dominican Republic from Isla Saona to the border with Haiti, St. Barthelemy and St. Martin.  Tropical Storm Watches have been issued for the Central Bahamas and the coast of the Dominican Republic from Isla Saona to Punta Palenque.

The circulation around Tropical Storm Erika is poorly organized to due persistent upper level winds from the west which are causing vertical wind shear.  The low level circulation consists of a large diffuse center with at least once smaller mesoscale center rotating around inside the larger diffuse center.  The mesoscale center could have been produced by one of the thunderstorm clusters that form nightly in the southeastern portion of the circulation.  Again on Thursday the strongest thunderstorms occurred east of the center of circulation.  Those thunderstorms produced a lot of upper level divergence but the upper level westerly winds pushed that divergence east of the low level center.  As a result, the surface pressure actually rose a couple of millibars on Thursday.  Stronger thunderstorms are forming southeast of the center of Erika again tonight.  So, the pattern of the past several nights appears to be repeating itself again.

An upper level trough over the western Caribbean Sea is causing the westerly winds that are the source of vertical wind shear over Erika.  That trough is expected to drift west and slowly weaken.  If it does weaken in a couple of days, then the upper level wind pattern could be more favorable for intensification.  However, the center of Erika could pass over or very near Hispaniola.  It is likely that the mountains on that island would significantly disrupt the low level circulation.  If the low level circulation maintains its integrity, the Sea Surface Temperatures around the Bahamas and south Florida are very warm.  If Erika still has a coherent circulation at that time it could organize quickly.

A subtropical ridge is steering Erika toward the west.  Erika is nearing the western end of the ridge and a turn toward the west-northwest is possible.  If Erika gets stronger and the circulation is taller, then the upper level trough could push it more toward the north.  On the other hand, if the circulation of Erika stays weaker and shorter, then lower level flow could push it farther west.  Erika is likely to pass near or over Hispaniola on Friday and on its anticipated track it could be approaching south Florida in about 72 hours.

Even if Erika is a disorganized tropical storm it is capable of producing heavy rains and flooding on any island it crosses.

Tropical Storm Erika Approaches the Leeward Islands

Tropical Storm Erika moved steadily toward the Leeward Islands on Wednesday.  At 11:00 p.m. EDT on Wednesday the center of Tropical Storm Erika was located at latitude 16.7°N and longitude 60.2°W which put it about 110 miles (175 km) east-southeast of Antigua and about 1400 miles east-southeast of Miami, Florida.  Erika was moving toward the west at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1006 mb.  Tropical Storm Warnings have been issued for Anguilla, Saba, St. Eustatius and St. Maarten, Puerto Rico, U.S. Virgin Islands, British Virgin Islands, Montserrat, Antigua, Barbuda, St. Kitts, Nevis, St. Martin and St. Barthelemy.  Tropical Storm Watches have been issued for the coast of the Dominican Republic from Cabo Engano to Cabo Frances Viejo, the southeastern Bahamas and the Turks and Caicos, and Guadeloupe.

Although Erika looks very impressive on infrared satellite images with a large area of cold cloud tops, it is in reality very poorly organized.  The thunderstorms generating those cold clouds are located southeast of the low level center of circulation.  There are not really any thunderstorms in other parts of Erika.  There could be a mid-level center of circulation within the cluster of thunderstorms southeast of the surface center.  Well organized tropical cyclones are vertically stacked with the mid-level center directly above the surface center.  This is certainly not the case with Erika.  Upper level winds from the west appear to be causing vertical wind shear over Erika and that is contributing to the poor organization.

Erika is moving over water where the Sea Surface temperature is almost 29°C.  So, there is sufficient energy in the upper ocean to support intensification.  However, an upper level trough over the central Caribbean Sea could continue to cause wind shear over Erika.  The intensity guidance is inconsistent.  Some guidance strengthens Erika to a hurricane during the next few days, while other guidance weakens it.  Until the circulation become more well organized and thunderstorms develop near the center of circulation, significant intensification is unlikely.  If the vertical wind shear gets any stronger it could weaken Erika to a tropical depression.

The track forecast is also challenging.  The numerical guidance shifted the track toward the east on Wednesday evening, but that was due to the fact that the models were predicting that Erika would become a stronger hurricane.  If it become a stronger storm with a taller, vertically coherent circulation, then the upper trough over the Caribbean could push Erika farther east.  However, if Erika remains weaker, then the winds in the lower levels of the atmosphere could push it farther to the west.  On its anticipated track Erika could approach southeastern Florida in about four days.

 

Tropical Storm Erika Prompts Warnings for the Caribbean

The imminent approach of Tropical Storm Erika prompted the issuance of watches and warnings for locations in the northeastern Caribbean Sea.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Erika was located at latitude 16.0°N and longitude 54.4°W which put it about 495 miles (800 km) east of Antigua and about 1780 miles (2870 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 18 m.p.h. (30 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1006 mb.  Tropical Storm Warnings have been issued for Anguilla, Saba, St. Eustatius, and St. Maarten.  Tropical Storm Watches have been issued for Puerto Rico, the U.S. Virgin Islands, the British Virgin Islands, Montserrat, Antigua, Barbuda, St. Kitts, Nevis, Guadeloupe, St. Martin and St. Barthelemy.

For much of Monday the circulation around Tropical Storm Erika consisted of a large swirl of low level clouds and a few thunderstorms well to the southeast of the center.  The minimum surface pressure rose several millibars which was indicative of a weakening storm.  In the past several hours satellite imagery suggests that a few new thunderstorms could be forming closer to the center of circulation.  Erika is moving over water where the Sea Surface Temperature (SST) is between 28°C and 29°C.  So there is plenty of energy in the upper ocean.  The circulation could be pulling in some drier air from farther north of the storm.  There is also some vertical wind shear which may also be inhibiting intensification.    The combination of positive environmental factors like SST and negative environmental factors like drier air and wind shear make the intensity forecast challenging.  Guidance from numerical models is divergent.  Some models predict intensification while others predict that Erika will dissipate like Danny did.  If more thunderstorms continue to develop around the center of circulation, then intensification would be more likely.  On the other hand, if the recently formed thunderstorms dissipate in a few hours, the Erika could weaken to a tropical depression.

A subtropical ridge is steering Erika a little north of due west and that general motion is expected to continue during the next several days.  On its anticipated track Erika would approach the northern Leeward Islands in about 24 hours and it could be near Puerto Rico in less than two days.

Danny Dissipates But Erika Forms Behind It

Vertical wind shear weakened Tropical Storm Danny as it entered the eastern Caribbean Sea and its circulation degenerated into a weak area of low pressure.  However, a new tropical storm formed about a thousand miles east of the remnants of Danny and the National Hurricane Center designated it as Tropical Storm Erika.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Erika was located at latitude 14.4°N and longitude 47.7°W which put it about 955 miles (1535 km) east of the Leeward Islands and about 2240 miles (3600 km) east-southeast of Miami, Florida.  Erika was moving toward the west at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1003 mb.

The circulation around Erika is a little larger than the circulation around Danny was.  There are several bands of thunderstorms near the center of circulation and the thunderstorms are generating upper level divergence in all directions.  Erika is moving over water where the Sea Surface Temperature is near 27.5°C and it will gradually move over warmer SSTs as it moves west.  Erika is moving at 20 m.p.h. and that is about the upper limit for storms that intensify over the tropical Atlantic Ocean.  Currently the low level winds and upper level winds are blowing at nearly the same speed.  So, there is not much vertical wind shear.  However, if Erika were to move toward the west faster, then vertical wind shear could be more significant.  As long as Erika does not move too fast, the environment is favorable for intensification and Danny intensified rapidly over the same region a few days ago.  When Erika enters the Caribbean Sea in two or three days, it could encounter the same upper level trough that sheared Danny apart.

A subtropical ridge is steering Erika quickly toward the west and that same general steering motion is expected to continue for the next two or three days.  Erika could be approaching the northern Leeward Islands in about 48 hours.

Tropical Storm Danny Approaching Dominica and Guadeloupe

Tropical Storm Danny weakened on Sunday but it was maintaining its status as a tropical storm as it approached Dominica and Guadeloupe.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Danny was located at latitude 15.6°N and longitude 59.8°W which put it about 115 miles (240 km) east-southeast of Guadeloupe and about 1415 miles (2280 km) east-southeast of Miami, Florida.  Danny was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1009 mb.  Tropical Storm Warnings have been issued for Antigua, Barbuda, Montserrat, St. Kitts and Nevis.  Tropical Storm Watches have been issued for Saba, St. Eustatius and St. Maarten.

Strong southwesterly winds in the upper levels created vertical wind shear which pushed the stronger thunderstorms northeast of the center of circulation.  The core of Tropical Storm Danny consisted of an area of low clouds rotating cyclonically for much of the Sunday, but satellite images and radar indicate that a few more showers and thunderstorms formed during the past few hours.  Danny still has a well defined low level circulation.  Thunderstorms northeast of the center were producing winds to tropical storm force and Danny was still classified as a Tropical Storm at 11:00 p.m. EDT on Sunday.

Upper level southwesterly winds are forecast to continue over the eastern Caribbean Sea.  The resulting vertical wind shear will make it difficult for thunderstorms to persist near the center of Tropical Storm Danny and it could weaken to a tropical depression at any time.  However, it is moving over warm water and a reduction in wind shear could allow for the circulation to maintain itself for a longer period if that happens.

A subtropical ridge north of Danny is steering the tropical storm toward the west and that general motion is expected to continue.  Danny will enter the eastern Caribbean Sea on Monday.  On its anticipated track Danny will pass south of Puerto Rico and it is unlikely to bring much rain to help alleviate the drought conditions there.  Danny could bring some wind and rain to the southern Leeward Islands as it passes over them during the next few hours.

Wind Shear Weakens Danny to a Tropical Storm

Strong upper level winds sheared the top off of Hurricane Danny on Saturday and it weakened to tropical storm intensity.  At 11:00 p.m. EDT on Saturday the center of Tropical Storm Danny was located at latitude 15.6°N and longitude 54.7°W which put it about 480 miles (775 km) east of the Leeward Islands and about 1760 miles (2840 km) east-southeast of Miami, Florida.  Danny was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 70 m.p.h. (110 km/h).  The minimum surface pressure was 999 mb.  Tropical Storm Watches have been issued for Antigua, Barbuda, Montserrat, St. Kitts, Nevis, Anguilla, Saba, St. Eustatius, St. Maarten, Gudaloupe, St. Barthelemy and St. Martin.

A upper level trough over the eastern Caribbean Sea generated brisk southwesterly winds over the top of Danny and blew the upper portion of the circulation northeast of the low level center.  By late Saturday afternoon the low level center was exposed on satellite imagery.  The vertical wind shear disrupted the vertical circulation of Danny and it weakened fairly quickly.  A few more thunderstorms appear to have developed northeast of the center in recent hours and the wind shear may have decreased just slightly.  Danny will move over slightly warmer water on Sunday, which could add a little more energy to the circulation.  The wind shear is forecast to continue and Danny could weaken further.

As Danny weakened, the lower portion of the circulation was steered more by the winds closer to the surface.  Those winds pushed the center more toward the west.  The subtropical ridge that was steering Danny is expected to strengthen and Danny is forecast to move toward the west for the next day or two.  On its anticipated track Danny could be near the Leeward Islands in about 30 hours and it could be approaching Puerto Rico in 48 hours.

Danny Becomes a Major Hurricane

Hurricane Danny intensified quickly and a NOAA plane investigating it on Friday afternoon found that Danny had maximum sustained winds of 115 m.p.h.  That made Danny a Category 3 hurricane on the Saffir-Simpson Scale which also made it a Major Hurricane.  At 5:00 p.m. EDT on Friday the center of Hurricane Danny was located at latitude 14.5°N and longitude 49.1°W which put it about 860 miles (1390 km) east of the Leeward Islands and about 2140 miles (3450 km) east-southeast of Miami, Florida.  Danny was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 115 m.p.h. (165 km/h) and there were wind gusts to 135 m.p.h. (195 km/h).  The minimum surface pressure was 974 mb.  Danny had a Hurricane Intensity Index (HII) of 20.6, a Hurricane Size Index (HSI) of 6.0, and a Hurricane Wind Intensity Size Index (HWISI) of 26.6

Danny remains a very small hurricane.  It is about two thirds of the size that Hurricane Charley was when it hit southwest Florida in 2004.  Danny may be starting to weaken.  The small eye is no longer visible on satellite images.  Southwesterly winds in the upper levels may be generating some vertical wind shear and those winds may also be inhibiting upper level divergence on the western side of Danny.  The small size of Danny means that it could weaken almost as fast as it intensified, if the shear increases.  Danny will move over warmer water when it passes west of longitude 55°W, which could slow the rate of weakening in about 36 hours.

Danny is being steered toward the west-northwest by a subtropical ridge located north of the hurricane.  The ridge is expected to strengthen in two or three days and steer Danny more toward the west after that time.  On its anticipated track Danny could be approaching the northern Leeward Islands in about two and a half days and it could be near Puerto Rico in about three and a half days.

Tiny Danny Quickly Intensifies Into a Hurricane

Tiny Tropical Storm Danny intensified quickly during the past 12 hours and the National Hurricane Center upgraded it to hurricane status in its 11:00 a.m. EDT advisory on Thursday.  At 11:00 a.m. EDT on Thursday the center of Hurricane Danny was located at latitude 12.5°N and longitude 44.8°W which put it about 1090 miles (1755 km) east of the Windward Islands and about 2480 miles (4000 km) east-southeast of Miami.  Danny was moving toward the west-northwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 992 mb.

The core of Hurricane Danny organized quickly on Thursday.  An eye formed in the center of the circulation and a ring of thunderstorms developed around the eye.  The circulation around Danny is very small.  Hurricane force winds only extend out about 12 miles (19 km) from the center and tropical storm force winds only extend 60 miles (95 km) from the center.  The Hurricane Size Index (HSI) for Danny is only 4.2.

The environment around Danny remains complex.  It is over water where the Sea Surface Temperature (SST) is near 28°C and the upper level winds are very light.  Upper level divergence is being produced by the thunderstorms around the eye.  On the other hand, slightly cooler SSTs and drier air are just to the north of Danny.  In addition, small hurricanes like Danny can be strongly affected by changes in their environment and they can intensify or weaken very quickly.  The environment would seem to support further intensification, but if Danny moves a little farther north, it could move into a more hostile environment.

Danny is being steered toward the west-northwest by the subtropical ridge to its north and that general steering pattern is expected to continue for another two or three days.  Late in the weekend the subtropical ridge is forecast to strengthen and steer Danny more toward the west.  On its anticipated track Danny could be near the Leeward Islands in about four days and near Puerto Rico in about five days.