Category Archives: Atlantic, Caribbean, and Gulf of Mexico

Atlantic TCs

Strong Low Spins Up Off Southeast Coast

A strong non-tropical low pressure system spun up off the Southeast Coast of the U.S. on Thursday and there is some possibility that it could eventually develop subtropical or tropical characteristics.   At 4:00 p.m. EST on Thursday the low pressure system was centered near latitude 29.0°N and longitude 74.0°W which put it about 425 miles (685 km) west-southwest of Bermuda.  The low was moving toward the east-northeast at 18 m.p.h. (29 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 994 mb.

The low pressure system exhibits the structure of an occluded extratropical cyclone.  An occluded front coils away from the low until it splits into a warm front and a cold front.  Drier air is being pulled around the western and southern sides of the low and a dry slot has formed in the southeastern quadrant of the storm.  However, upper level divergence is pumping mass away from the center of the low and the surface pressure decreased quickly on Thursday afternoon.

The low is in an environment that is not favorable for the classical scenario of formation of a tropical cyclone.  It is moving over water where the Sea Surface Temperature (SST) is near 25°C and strong upper level winds are creating significant vertical wind shear.  However, research has shown that it is possible to get a transition to a subtropical or tropical cyclone over cooler SSTs, when a low pressure system moves into an area where the wind shear is less.

A trough over the southeastern U.S. is steering the low pressure system toward the east-northeast and that general motion is expected to continue during the next day or two.  An upper level ridge is forecast to move north of the low pressure system in a couple of days.  The upper level ridge is expected to steer the low pressure system toward the east-southeast early next week.

If the low pressure system takes the expected track, it could eventually move over slightly warmer SSTs and into an area where there is less vertical wind shear.  The more favorable environment could cause the structure of the low to change into a more subtropical or tropical form.  The National Hurricane Center is giving the low a 10% chance of transitioning into a subtropical cyclone during the next 48 hours and a 30% chance that it makes that transition during the next five days.

Kate Becomes a Hurricane As It Races Northeast

Kate intensified into the fourth Atlantic hurricane of 2015 as it raced northeastward.  At 10:00 a.m. EST on Wednesday the center of Hurricane Kate was located at latitude 36.8°N and longitude 60.5°W which put it about 395 miles (635 km) northeast of Bermuda and about 780 miles (1160 km) south-southwest of Cape Race, Newfoundland.  Kate was moving toward the northeast at 45 m.p.h. (72 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 985 mb.

The organization of Hurricane Kate improved on Wednesday when a partial eyewall wrapped around the northern and western sides of the center of circulation.  The structure of Kate is somewhat tilted toward the northeast by stronger southwesterly wind in the upper levels of the atmosphere.  However, Kate currently has a warm core and it is still a tropical cyclone.  Kate is moving over water where the Sea Surface Temperature (SST) is near 25°C.  In a day or so the effects of strong vertical wind shear and cooler SSTs will cause Hurricane Kate to begin a transition to an extratropical cyclone.

Strong westerly winds are steering Kate rapidly toward the northeast and that general motion is expected to continue during the next few days.  Kate could approach the United Kingdom as a strong extratropical cyclone during the weekend.

Tropical Storm Kate Intensifies and Moves Away from the Bahamas

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.

Tropical Depression 12 Forms and Warnings Issued for the Bahamas

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.

Disturbance Brings Squally Weather to the Northwest Caribbean Sea

A complicated disturbance over the northwestern Caribbean Sea is bringing squally weather to that area.  A tropical wave over the western Caribbean Sea is interacting with an upper level low over eastern Mexico.  The disturbance is causing thunderstorms over a region that extends from the northwestern Caribbean Sea to the southern Gulf of Mexico.  Upper level divergence east of the upper low has led to the formation of a surface low pressure system east of Belize.  At 7:00 p.m. EST on Thursday the center of the surface low was located at latitude 18°N and longitude 86°W which put it about 150 miles (240 km) east-southeast of Chetumal, Mexico.  The surface low was moving toward the west-northwest at 10 m.p.h. (16 m.p.h.).  The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h).  The minimum surface pressure was 1011 mb.

The disturbance is not very well organized, which is normally the case when a tropical wave interacts with an upper level low.  There is a broken area of thunderstorms that extends around the east and northern sides of the disturbance.  However, there are not many thunderstorms close to the center of the surface low.  The upper low is causing vertical wind shear over the western half of the surface low.  Some upper level divergence is occurring over the eastern half of the surface low.

A large high pressure system over the western Atlantic Ocean is steering the disturbance toward the west-northwest.  That general steering pattern is expected to continue for the next two days.  On its anticipated track the disturbance will move over the Yucatan peninsula and over the southern Gulf of Mexico during the next several days.

The disturbance is in an environment that is marginally favorable for tropical development.  The Sea Surface Temperature of the northwestern Caribbean is near 29°C.  There is vertical wind shear, but it may be just small enough to allow for slow development.  On the other hand, the disturbance will move over the Yucatan peninsula which will further inhibit development.  There may also be a chance for development after the disturbance moves over the southern Gulf of Mexico.  The National Hurricane Center is giving a 20% probability of tropical cyclone formation out of the disturbance.

Hurricane Joaquin Passing Northwest of Bermuda

Hurricane Joaquin is bringing tropical storm force winds to Bermuda as the core of the hurricane moves northwest of that island.  Wind gusts to 64 m.p.h. have been reported in recent hours in Bermuda.  At 11:00 p.m. EDT on Sunday the center of Hurricane Joaquin was located at latitude 33.1°N and longitude 65.5°W which put it about 70 miles (110 km) northwest of Bermuda.  Joaquin was moving toward the north-northeast at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 961 mb.  A Hurricane Warning remains in effect for Bermuda.

Hurricane Joaquin is gradually moving over cooler water, but it is still over water where the Sea Surface Temperature is around 28°C.  It appears that a combination of drier air and vertical wind shear caused Joaquin to weaken on Sunday.  Thunderstorms are not rising as far up into the atmosphere and gaps have appeared in the eyewall.  Southwesterly winds in the upper levels are inhibiting upper level divergence in that portion of the hurricane and the pressure rose 17 mb on Sunday.  The wind shear could lessen for a time on Monday and the rate of weakening could slow.

Hurricane Joaquin is moving toward the north-northeast.  When it moves farther north, it will encounter the upper level westerlies in the middle latitudes.  Those westerly winds will carry Joaquin toward the east.  Joaquin could make a transition to a strong extratropical storm and affect western Europe in a few days.

Hurricane Joaquin Heading Toward Bermuda

After intensifying to almost Category 5 on the Saffir-Simpson Scale on Saturday, Hurricane Joaquin headed toward Bermuda.  The Bermuda Weather Service has issued a Hurricane Warning for Bermuda.  At 11:00 p.m. EDT on Saturday the center of Hurricane Joaquin was located at latitude 28.0°N and longitude 68.9°W which put it about 385 miles (620 km) southwest of Bermuda.  Joaquin was moving toward the northeast at 20 m.p.h. (32 km/h).  The maximum sustained wind speed was 130 m.p.h. (215 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 944 mb.  Joaquin was a Category 4 hurricane on the Saffir-Simpson Scale.  The Hurricane Intensity Index (HII) was 25.1.  The Hurricane Size Index (HSI) was 20.0 and the Hurricane Wind Intensity Size Index (HWISI) was 45.1.

Joaquin is moving over water where the Sea Surface Temperature is near 29°C.  However, a large upper level trough over the southeastern U.S. and an upper level low northwest of Joaquin are combining to generate westerly winds over the hurricane.  The vertical wind shear is causing the circulation to become more asymmetrical and the strongest convection is occurring in the eastern half of the circulation.  The flow of air is also pushing drier air toward the core of Hurricane Joaquin.  If Joaquin can move fast enough to outrun the drier air, it could weaken slowly.  However, if the drier air gets into the core of the circulation, then Joaquin will weaken faster.

The trough and upper level low are steering Hurricane Joaquin quickly toward the northeast and that motion is expected to continue on Sunday.  On its anticipated track Joaquin will pass near Bermuda on Sunday night.  It could bring strong winds and a storm surge as it moves past the island.

Hurricane Joaquin Moving Slowly Away from the Bahamas

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.

Category 4 Hurricane Joaquin Bringing Strong Winds and Floods to the Bahamas

Hurricane Joaquin intensified to Category 4 on the Saffir-Simpson Scale on Thursday and it brought strong winds and floods to some of the islands of the Bahamas.  At 11:00 p.m. EDT on Thursday the center of Hurricane Joaquin was located at latitude 22.9°N and longitude 74.6°W which put it about 20 miles (32 km) east-southeast of Clarence Town on Long Island in the Central Bahamas and about 810 miles (1310 km) south of Cape Hatteras, North Carolina.  Joaquin was moving toward the west at 3 m.p.h. (5 km/h).  The maximum sustained wind speed was 130 m.p.h. (210 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 935 mb.  The Hurricane Intensity Index (HII) was 25.1.  The Hurricane Size Index (HSI) was 21.4 and the Hurricane Wind Intensity Size Index (HWISI) was 46.5.

A Hurricane Warning has been issued for the Central Bahamas including Cat Island, Rum Cay, the Exumas, Long Island 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 Ragged Islands, the Inaguas, Mayaguana and the Turks and Caicos.  A Tropical Storm Warning has been issued for the Cuban provinces of Camaguey, Los Tunas, Holguin and Guantanamo.

The eye in Hurricane Joaquin contracted on Thursday and it has only been visible intermittently on conventional satellite imagery.  The intensity of the hurricane appears to have stabilized in recent hours.  While the intensity of Joaquin has been constant, the circulation has increased in sized and hurricane force winds now extend out about 50 miles (80 km) from the center.  Joaquin is still generating upper level divergence which seems to be pumping out as much mass as is converging in the lower levels of the circulation.  As a result, the pressure has also remained fairly steady during the past few hours.  There is not much vertical wind shear and the overall environment would seems to support further intensification.  However, the slow movement of Joaquin may be causing it to stir cooler water to the surface, which will reduce the energy available to the hurricane.

Hurricane Joaquin has moved little during the past six hours.  An narrow ridge is blocking its motion and the ridge is preventing it from moving toward the north.  A large upper level trough over the eastern U.S. is expected to weaken the ridge on Friday.  The upper level trough is expected to steer Joaquin toward the north on Friday.  Most of the reliable numerical models predict that the trough will carry Joaquin toward the northeast during the weekend and that it will stay east of the U.S.  A couple of other models still suggest a landfall could occur, but they are outliers at the current time.  Until Hurricane Joaquin makes the turn toward the north and northeast, it could still pose a potential risk to the U.S., but that possibility is much less than it was 24 hours ago.  Joaquin will continue to bring high winds and floods to parts of the Bahamas on Friday.

Joaquin Becomes a Major Hurricane Near the Bahamas

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.