Hurricane Irma strengthened rapidly as it moved over the tropical Atlantic Ocean. At 11:00 a.m. EDT on Thursday the center of Hurricane Irma was located at latitude 16.9°N and longitude 33.8°W which put it about 1845 miles (2975 km) east of the Leeward Islands. Irma was moving toward the west-northwest at 10 m.p.h. (16 km/h). The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h). The minimum surface pressure was 979 mb.
Hurricane Irma intensified rapidly on Thursday morning. A circular eye developed at the center of circulation and a ring of strong thunderstorms surrounded the eye. Numerous bands of showers and thunderstorms developed outside the core of Irma. Hurricane Irma has a very circular, symmetrical shape. Thunderstorms in the core of Irma were generating strong upper level divergence which was pumping mass away in all directions from the hurricane.
Hurricane Irma will move through an environment favorable for intensification during the next few days. Irma will move over water where the Sea Surface Temperature is near 28°C. Irma is under the western end of an upper level ridge, but the upper level winds are weak and there is not much vertical wind shear. Irma is likely to intensify during the next few days and it is forecast to become a major hurricane. Hurricanes that intensify rapidly often develop concentric eyewalls, which cause fluctuations in their intensity. It is highly likely that Hurricane Irma will go through one of more eyewall replacement cycles which will cause temporary fluctuations in the wind speed. Eyewall replacement cycles often result in a larger hurricane and Hurricane Irma has the potential to develop into a big classic Cape Verde hurricane.
Hurricane Irma is nearing a weaker region in the subtropical ridge to its north. The weakness is allowing Irma to move toward the west-northwest. The ridge is expected to strengthen and steer Hurricane Irma more toward the west or west-southwest during the next few days. On its anticipated track Hurricane Irma is forecast to be a major hurricane east of the Leeward Islands in five days. The uncertainty about the future track of Hurricane Irma increases after that time. People around the western Atlantic need to monitor the progress of Hurricane Irma.
Tropical Depression 12 intensified Monday into Tropical Storm Kate. Kate continued to intensify on Monday night as it started to move away from the Bahamas. At 10:00 p.m. EST on Monday the center of Tropical Storm Kate was located at latitude 27.2°N and longitude 76.0°W which put it about 175 miles (280 km) north-northeast of the Northwestern Bahamas. Kate was moving toward the north 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 1005 mb.
Kate is more organized this evening and it looks more like a tropical storm. The is a core of thunderstorms at the center of circulation and several rainbands are wrapping around the northeastern side of the storm. Kate has a small circulation and tropical storm force winds only extend out about 80 miles (130 km) on the eastern side of it. The thunderstorms in the core of Kate are generating upper level divergence which is spreading northeast of the center.
Tropical Storm Kate is in an environment that is favorable for further intensification. It is over water where the Sea Surface Temperature is near 28°C. The combination of a large trough west of Kate and a smaller upper level high east of it are creating some southerly winds over the top of the circulation. However, the vertical wind shear is moderate at the current time, and Kate could intensify further. Kate could reach hurricane intensity in the next 24 to 36 hours. After that time the trough to the west of Kate will cause increased vertical wind shear.
The upper level trough and ridge are steering Kate toward the north. As Kate moves farther north, stronger westerly winds will begin to push it toward the northeast. Since Kate is moving toward the northeast away from the Bahamas, the government there has discontinued all tropical storm warnings.
A small center of circulation developed within a larger disturbance near the Bahamas and the National Hurricane Center classified it as Tropical Depression 12 (TD12). At 10:00 p.m. EDT on Sunday the center of Tropical Depression 12 was located at latitude 23.0°N and longitude 73.0°W which put it about 115 miles (185 km) southeast of San Salvador in the Bahamas and about 30 miles (50 km) north of Mayaguana. TD12 was moving toward the northwest at 14 m.p.h. (22 km/h). The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h). The minimum surface pressure was 1010 mb.
Tropical Storm Warnings have been issued for the Central and Northwestern Bahamas and for the Acklins, Samana Cays, Crooked Island and Long Cay in the Southeastern Bahamas.
Tropical Depression 12 formed when a tropical wave interacted an upper level low. Tropical cyclones that develop in that manner tend to be poorly organized in their early stages. Most of the stronger thunderstorms are located east and south of the center of circulation. The surface center is located on the western edge of the convection.
Although Tropical Depression 12 is over water where the Sea Surface Temperature is near 28°C, the upper level environment is marginal for intensification. An upper level low near southwest of the depression is generating southerly upper level winds over the western part of TD12. A small upper level high is over the eastern part of TD12. The upper level high is generating some divergence to the east of the depression. Some further intensification is possible and the depression could become Tropical Storm Kate on Monday.
Tropical Depression 12 could bring rain and squally weather to parts of the Bahamas. It is near some of the same places that were hit by Hurricane Joaquin last month and it could hinder recovery efforts.
Hurricane Joaquin turned northward on Friday and it is starting to move slowly away from the Central Bahamas. However, it is still producing strong winds, heavy rain and storm surges on San Salvador and nearby islands. At 5:00 p.m. EDT on Friday the center of Hurricane Joaquin was located at latitude 24.1°N and longitude 74.7°W which put it about 15 miles (25 km) west-northwest of San Salvador in the Central Bahamas and about 745 miles (1200 km) south of Cape Hatteras, North Carolina. Joaquin was moving toward the north at 7 m.p.h. (11 km/h). The maximum sustained wind speed was 125 m.p.h. (205 km/h) which made Joaquin a Category 3 hurricane on the Saffir-Simpson Scale. There were wind gusts to 155 m.p.h. (250 km/h) and the minimum surface pressure was 942 mb. The Hurricane Intensity Index (HII) was 23.6. The Hurricane Size Index (HSI) was 20.3 and the Hurricane Wind Intensity Size Index (HWISI) was 43.9.
A Hurricane Warning is in effect for the Central Bahamas including Cat Island, the Exumas, Rum Cay, Long Island and San Salvador. A Hurricane Warning is in effect for the Northwestern Bahamas including the Abacos, Berry Island, Eleuthera, Grand Bahama Island and New Providence. A Hurricane Watch has been issued for Bimini and Andros Island. A Tropical Storm Warning is in effect for Andros Island and the Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayaguana, the Ragged Islands and the Turks and Caicos. A Tropical Storm Watch has been issued for Bermuda.
Hurricane Joaquin did not change a lot on Friday, although there were some indications that vertical wind shear may be starting to affect it. Microwave satellite imagery and aerial reconnaissance indicate that there is still and eye, although the eyewall is thinner on the north side. Most of the stronger thunderstorms are on the southern side of the circulation. An upper level trough over the eastern U.S. may be creating stronger winds that are hitting Joaquin from the southwest. Those southwesterly winds may be limiting upper level divergence on that side of the hurricane. The hurricane is still over water where the Sea Surface Temperature is near 30°C. So, vertical wind shear is the only factor inhibiting intensification. The trough is expected to produce more vertical wind shear on Saturday, which could start to weaken Joaquin.
The upper level trough is starting to steer Joaquin slowly toward the north. The trough is expected to steer Joaquin toward the northeast at a faster rate during the next several days. Guidance from all of the numerical models has come into agreement that Joaquin will stay east of the U.S. Conditions in the Central Bahamas should improve on Saturday as Hurricane Joaquin moves farther away. The possibility that Joaquin could be near to Bermuda on Sunday prompted the issuance of a Tropical Storm Watch for that island.
Hurricane Joaquin intensified very rapidly on Wednesday and it reached Major Hurricane intensity. At 11:00 p.m. EDT on Wednesday night the center of Hurricane Joaquin was located at latitude 23.8°N and longitude 73.1°W which put it about 90 miles (145 km) east of San Salvador and about 750 miles (1215 km) south-southeast of Cape Hatteras, North Carolina. Joaquin was moving toward the southwest at 6 m.p.h. (10 km/h). The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 140 m.p.h. (220 km/h). The wind speed made Joaquin a Category 3 hurricane on the Saffir-Simpson Scale and a Major Hurricane. The minimum surface pressure was 951 mb. The Hurricane Intensity Index (HII) was 20.6, the Hurricane Size Index (HSI) was 11.6, and the Hurricane Wind Intensity Size Index (HWISI) was 32.2.
A Hurricane Warning has been issued for the Central Bahamas including Cat Island, the Exumas, Long Island, Rum Cay and San Salvador. A Hurricane Warning has been issued for the Northwestern Bahamas including the Abacos, Berry Islands, Eleuthera, Grand Bahama Island and New Providence. A Hurricane Watch has been issued for Bimini and Andros Island. A Tropical Storm Warning has been issued for Andros Island and the Southeastern Bahamas including the Acklins, Crooked Island, Long Cay, the Inaguas, Mayguana and the Ragged Islands.
Joaquin has a well formed structure. The circulation is fairly symmetrical, although there are more spiral bands of thunderstorms south and east of the center. The hurricane is over water where the Sea Surface Temperature is near 30°C. A narrow upper level ridge west of Joaquin is causing light northerly winds over the circulation, but those winds did not inhibit rapid intensification on Wednesday. The convection generated upper level divergence which pumped out mass and caused the pressure to decrease quickly. Further intensification is possible during the next 24 hours, although if an eyewall replacement occurs, it would interrupt that process. An upper level trough over the eastern U.S. will generate more vertical wind shear in a day or two and Joaquin will start to weaken.
A ridge north of Joaquin is blocking the hurricane and forcing it to move toward the southwest. The ridge will weaken in a day or so and the upper level trough will start to steer Joaquin toward the north. When the hurricane starts moving northward, it will also begin to move faster. It could be approaching the Mid-Atlantic Coast by later on Saturday.
Tropical Storm Joaquin is on the verge of reaching hurricane intensity. At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Joaquin was located at latitude 25.8°N and longitude 71.7°W which put it about 360 miles (580 km) east of the Northwestern Bahamas and about 680 miles (1100 km) south-southeast of Cape Hatteras, North Carolina. Joaquin was moving toward the west-southwest at 5 m.p.h. (8 km/h). The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h). The minimum surface pressure was 988 mb. The government of the Bahamas has issued a Hurricane Watch for the Central Bahamas.
The organization of the circulation of Tropical Storm Joaquin increased on Tuesday in spite of moderate amounts of vertical wind shear. More thunderstorms developed near the core of circulation and a partial eyewall formed around the southern and eastern parts of the center. Although it is more organized, the circulation is still asymmetrical and the stronger winds were found in the eastern side of the tropical storm.
A thin upper level ridge is east of Florida and clockwise flow around the ridge is producing northerly winds over the top of Joaquin. Those winds produced moderate vertical wind shear on Tuesday but the shear appears to be decreasing with time. Joaquin is over water where the Sea Surface Temperature is near 30°C. As the upper level winds diminish, the environment favors intensification and Joaquin is likely to become a hurricane on Wednesday. Joaquin will continue to be in an environment that favors intensification during the next several days.
A ridge of high pressure north of Joaquin is blocking it from moving north and the ridge is forcing the tropical storm to move toward the west-southwest. That general motion is expected to continue for another 24 to 48 hours and it could bring Joaquin near the Central and Northwestern Bahamas. When Joaquin reaches the western end of the ridge it will turn toward the north. An upper level trough over the eastern U.S. will cause Joaquin to move more quickly toward the north at the end of the week. On its anticipated track, Joaquin could be approaching the Mid-Atlantic Coast of the U.S. by the weekend.
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.
Reconnaissance aircraft found that the maximum sustained wind speed in Tropical Depression Four has increased to 45 m.p.h. and it has been upgraded to Tropical Storm Cristobal. At 8:00 a.m. EDT the center of Cristobal was located at latitude 23.0°N and longitude 73.0°W which put it about 135 miles east-southeast of Long Island in the Bahamas and about 480 miles east-southeast of Miami, Florida. Cristobal was moving toward the northwest at 9 m.p.h. The minimum surface pressure was 1002 mb. Tropical Storm Warnings remain in effect for the Southeastern and Central Bahamas and the Turks and Caicos.
Upper level winds from the northwest appear to be creating wind shear over Cristobal. Most of the convection is occurring east and south of the center.
A reconnaissance aircraft found westerly winds in the southeastern side of a low pressure system over the Southeastern Bahamas and was able to close off a center of circulation. As a result the National Hurricane Center classified the low as Tropical Depression Four (TD4). At 5:00 p.m. EDT on Saturday the center of TD4 was located at latitude 21.8°N and longitude 72.3°W which put it about 75 miles northeast of Great Inagua Island in the Bahamas and about 560 miles east-southeast of Miami, Florida. TD4 was moving toward the northwest at 12 m.p.h. The maximum sustained wind speed was 35 m.p.h. and the minimum surface pressure was 1005 mb.
Tropical Storm Warnings have been issued for the Southeastern Bahamas including The Acklins, Crooked Island, Long Cay, The Inaguas, Mayaguana and the Ragged Islands as well as The Turks and Caicos Islands and the Central Bahamas including Cat Island, The Exumas, Long Island, Rum Cay and San Salvador.
A small upper low north of Cuba is causing some wind shear over the western portion of TD4. On the other hand the Sea Surface Temperatures around The Bahamas are very warm and TD4 is very likely to intensify into Tropical Storm Cristobal and eventually into a hurricane. Since the center has just formed the motion and future track are still highly uncertain, although a general motion toward the southeastern U.S. seems likely.
The circulation around the tropical disturbance designated 96L has been disrupted by the mountains on Hispaniola. There a appears to be a broad low level center near the northern coast of Haiti. There are several smaller vorticies rotating around within the broader area of low pressure. The strongest winds are occurring north and east of the center and several reconnaissance flights found winds to tropical storm force north of the center. The broad center appears to be moving toward the west-northwest at 10-15 m.p.h. The area of low pressure has produced heavy rain on some of the islands of the northern Caribbean Sea.
It is still possible that 96L could organize into a tropical cyclone as it moves away from Hispaniola. Once it gets away from the mountains, it will be easier for the flow to consolidate around one primary circulation center. The Sea Surface Temperatures (SSTs) are very warm around the Bahamas and the upper level winds are not too strong.
There is a large amount of uncertainty about the future track of this system and that will continue until a well defined center of circulation exists. It appears that the low has been initialized too far to the northeast in some runs of numerical models and that has produced some forecast tracks that are also too far north and east. It is still possible that this system could head in the general direction of the southeastern U.S.
Development will possibly be slow to occur until the system becomes better organized. Tropical cyclones can intensify rapidly over the Bahamas and people would be wise to monitor future developments with 96L.