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Cat. 5 Hurricane Irma Moving Over Northern Leeward Islands

Category 5 Hurricane Irma moved over the northern Leeward Islands on Wednesday morning.  At 5:00 a.m. EDT on Wednesday the center of Hurricane Irma was located at latitude 17.9°N and longitude 62.6°W which put it about 35 miles (55 km) east-southeast of St. Martin.  Irma was moving toward the west-northwest at 16 m.p.h. (26 km/h).  The maximum sustained wind speed was 185 m.p.h. (295 km/h) and there were wind gusts to 210 m.p.h. (340 km/h).  The minimum surface pressure was 912 mb.

The core of Hurricane Irma moved across Antigua, Barbuda, St. Barthelemy and St. Martin in recent hours.  It will reach Anguilla later this morning.

Hurricane Watches were in effect for Antigua, Anguilla, Barbuda, Montserrat, St. Kitts, Nevis, Saba, St. Eustatius, Sint Maarten, St. Martin, St. Barthelemy, the British Virgin Islands, the U.S. Virgin Islands, Puerto Rico, Vieques, Culebra, Guadeloupe, the southeastern Bahamas including the Acklins, Cooked Islands, Long Cay, the Iguanas, Mayaguane, the Ragged Islands, the Turks and Caicos, and the portion of the coast of Cabo Engano, Dominican Republic to the northern border with Haiti.  Hurricane Watches are in effect for the central Bahamas, the portion of the coast from Le Mole St. Nicholas to the northern border with Haiti and from Matanzas province to Guantanamo province in Cuba.  A Tropical Storm Warning is in effect for the portion of the coast from Cabo Engano, Dominican Republic to the southern border with Haiti.  A Tropical Storm Watch is in effect for the portion of the coast from Le Mole St. Nicolas, Haiti to Port Au Prince.

Hurricane Irma maintained its intensity during the northern overnight hours.  It has a circular eye with a diameter of 30 miles (48 km).  The eye is surrounded by a ring of strong thunderstorms and the strongest winds are occurring in that ring of storms.  Winds to hurricane force extend out about 60 miles (95 km) from the center.  Winds to tropical storm force extend out about 160 miles (260 km) from the center.

The Hurricane Intensity Index (HII) is 44.1.  The Hurricane Size Index (HSI) is 19.8 and the Hurricane Wind Intensity Size Index (HWISI) is 63.9.  Those indices indicate that Hurricane Irma is capable of causing widespread catastrophic wind damage.

Hurricane Irma will continue to move over an environment very favorable for hurricanes.  Irma will stay over water where the Sea Surface Temperature is near 30°C.  The upper level winds will remain weak for several more days and there will be little wind shear.  An upper level trough over the eastern U.S. will produce strong winds when Irma gets closer to Florida.  The wind shear will increase at that time.  Hurricane Irma could go through eyewall replacement cycles which would cause fluctuations in intensity.

Hurricane Irma is moving near the western end of a subtropical high pressure system over the Atlantic Ocean which is steering Irma toward the west-northwest.  The west-northwesterly motion is expected to continue for several more days.  Eventually, the upper level trough over the eastern U.S. is forecast to turn Hurricane Irma toward the north when it approaches Florida.  On its anticipated track the center of Hurricane Irma is forecast to pass north of Puerto Rico and Hispaniola.

Elsewhere, Tropical Storm Jose is trailing behind Hurricane Irma and Tropical Storm Katia has developed over the southern Gulf of Mexico.  At 5:00 a.m. EDT on Wednesday the center of Tropical Storm Jose was located at latitude 12.5°N and longitude 42.8°W which put it about 1255 miles east of the Leeward Islands.  Jose was moving toward the west at 13 m.p.h. (20 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 1002 mb.

At 5:00 a.m. EDT on Wednesday the center of Tropical Storm Katia was located at latitude 22.1°N and longitude 96.3°W which put it about 105 miles (165 km) east of Tampico, Mexico.  Katia was moving toward the east at 2 m.p.h. (3 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 Karl Approaching Bermuda

Tropical Storm Karl continued to move steadily toward Bermuda on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Karl was located at latitude 29.9°N and longitude 65.1°W which put it about 165 miles (270 km) south of Bermuda.  Karl was moving toward the north at 13 m.p.h. (20 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 988 mb.

A Hurricane Watch has been issued for Bermuda.  A Tropical Storm Warning is also in effect for Bemruda.

Tropical Storm Karl strengthened on Friday, but its structure remained asymmetrical.  Almost all of the thunderstorms are in a primary rainband that wraps around the northern and western sides of the center of circulation.  There are few if any thunderstorms south and east of the center.  It appears as it vertical wind shear is tilting the circulation toward the northwest.  The upper level center appears to be located 20 to 30 miles (30 to 50 km) northwest of the low level center.  The thunderstorms in the primary rainband are producing upper level divergence which is pumping out mass to the east of Tropical Storm Karl.  The upper level divergence pumped out enough mass on Friday to allow the surface pressure to decrease by about 10 mb.  However, the vertical wind shear and lack of thunderstorms to the east of the center limited the increase in wind speed at the surface.

Tropical Storm Karl is moving over water where the Sea Surface Temperature is near 29°C.  So, there is enough energy in the upper ocean to support a stronger storm.  However, an upper level trough to the west of Karl is creating significant vertical wind shear, which is likely to limit intensification in the short term.  When Tropical Storm Karl, turns east and moves farther from the upper level trough, the shear could decrease and Karl could strengthen.  In addition Karl will begin a transition to an extratropical cyclone and that transition often produces and increase in the wind speed.  So, Tropical Storm Karl does have a chance to become a hurricane during the weekend.

Tropical Storm Karl is moving around the western end of a subtropical ridge which is steering it toward the north.  It is likely to keep moving in that direction for another six to twelve hours.  When Tropical Storm Karl nears Bermuda it will encounter stronger westerly winds which will turn it eastward.  Karl is likely to move quickly toward the east-northeast on Saturday and Sunday.  On its anticipated track Tropical Storm Karl will pass near Bermuda on Saturday morning.  It will bring a period of gusty winds and heavy rain.

Karl Becomes a Tropical Storm Again and Warning Issued for Bermuda

Reconnaissance aircraft investigating Tropical Depression Karl on Thursday afternoon found that it had intensified into a tropical storm again and a Tropical Storm Warning was issued for Bermuda.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Karl was located at latitude 25.5°N and longitude 63.2°W which put it about 480 miles (770 km) south-southeast of Bermuda.  Karl was moving toward the northwest at 16 m.p.h. (26 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 1005 mb.

The structure of Tropical Storm Karl became more organized on Thursday, but the circulation is not well organized.  Most of the thunderstorms are occurring in a primary rainband that spirals around the eastern and northern portions of the circulation.  There are other fragmented rainbands farther to the east of the center of circulation.  There are few thunderstorms or bands south and west of the center and there may be drier air in that part of Tropical Storm Karl.  Thunderstorms in the primary rainband were beginning to generate some upper level divergence.

Tropical Storm Karl is moving into an environment that is more favorable for intensification.  Karl is moving farther away from an upper level low that is west of the the tropical storm.  As the distance between Tropical Storm Karl and the upper low increases, the vertical wind shear will decrease.  Karl is moving over water where the Sea Surface Temperature is near 30°C.  Tropical Storm Karl is likely to intensify slowly until the primary rainband wraps around the center of circulation.  If a tight inner core develops at the center of Karl, then it could intensify more quickly after that happens.

Tropical Storm Karl is moving around the western end of a subtropical high pressure system.  The high is steering Karl in a generally northwesterly direction.  Karl is likely to move more toward the north as it goes around the western end of the high.  When Karl gets northwest of the axis of the high pressure system, the westerly winds in the middle latitudes will start to turn it more toward the northeast.  On its anticipated track, Tropical Storm Karl could be near Bermuda in about 36 hours.  Tropical Storm Karl could bring wind and rain to Bermuda during the weekend.

 

Tropical Storm Karl Intensifies a Little

After several days when Tropical Storm Karl was poorly organized and barely maintained tropical storm intensity, Karl intensified a little late on Monday.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Karl was located at latitude 19.7°N and longitude 50.5°W which put it about 760 miles (1225 km) east-northeast of the Leeward Islands.  Karl was moving toward the west-northwest at 14 m.p.h. (22 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 1005 mb.

Although the structure of Tropical Storm Karl improved a little during the past few hours, it is still not a well organized storm.  A cluster of thunderstorms (sometimes called a Central Dense Overcast or CDO) formed near the core of Tropical Storm Karl.  Additional thunderstorms developed in fragmented rainbands, which are primarily in the eastern half of the circulation.  The cluster of thunderstorms near the core of the circulation is beginning to generate upper level divergence.

Tropical Storm Karl is moving into a more favorable environment.  It is moving over water where the Sea Surface Temperature (SST) is near 28°C.  An upper level low to the west of Karl has been causing strong vertical wind shear over the top of the tropical storm.  However, the upper low is moving farther west of Karl and the vertical wind shear is lessening.  Warm SSTs and less vertical wind shear allowed Tropical Storm Karl to begin to get a little better organized.  Karl is likely to intensify slowly while the circulation organizes and a more well define structure develops.  Tropical Storm Karl will move over warmer SSTs during the next few days and it is forecast to become a hurricane later this week.

Tropical Storm Karl is moving around the southwestern portion of a subtropical ridge which is steering it toward the west-northwest.  Karl is likely to turn more toward the northwest during the next several days.  On its anticipated track Tropical Storm Karl is likely to move northeast of the Leeward Islands and head in the general direction of Bermuda.

Tropical Storm Karl Develops over the Eastern Atlantic

More thunderstorms developed near the center of Tropical Depression 12 and the National Hurricane Center named it Tropical Storm Karl on Thursday night.  Karl is the third tropical storm to form over the Atlantic Ocean this week.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Karl was located at latitude 17.9°N and longitude 32.5°W which put it about 1930 miles (3150 km) east of the Leeward Islands.  Karl was moving toward the west at 14 m.p.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 1005 mb.

The circulation of Tropical Storm Karl is asymmetrical.  Karl does have a large circular low level wind fields.  However the thunderstorms are northeast of the center of circulation, although some thunderstorms have developed closer to the northeast side of the center in recent hours.  Southwesterly winds in the upper levels are generating moderate vertical wind shear, which has contributed to the asymmetrical distribution of thunderstorms.  In addition, the upper level winds are inhibiting upper level divergence to the west of Tropical Storm Karl.

Tropical Storm Karl is moving through an environment that is not very favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 27°C.  There is moderate vertical wind shear, which will make it hard for thunderstorms to persist near the center of the tropical storm.  Karl could move into an area where the upper level winds are not as strong in a day or two.  The environment could be more favorable for intensification at that time.

A subtropical ridge north of Karl is steering the tropical storm toward the west.  The ridge is expected to get stronger and it should steer Tropical Storm Karl toward the west or west-southwest during the next few 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.