Tag Archives: the Bahamas

Hurricane Matthew Becomes the First Category 5 Atlantic Hurricane Since 2007

Hurricane Matthew continued its rapid intensification on Friday night and it became the first Atlantic hurricane to reach Category 5 on the Saffir-Simpson Scale since Hurricane Felix did so in 2007.  At 11:00 p.m. EDT on Friday the center of Hurricane Matthew was located at latitude 13.3°N and longitude 72.3°W which put it about 440 miles (710 km) southeast of Kingston, Jamaica.  Matthew was moving toward the west at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 160 m.p.h. (260 km/h) and there were wind gusts to 190 m.p.h. (305 km/h).  The minimum surface pressure was 941 mb.

The Hurricane Intensity Index (HII) for Matthew was 35.0.  The Hurricane Size Index (HSI) was 13.7 and the Hurricane Wind Intensity Size Index (HWISI) was 48.7.  These indices indicate that Hurricane Matthew is not as intense and slightly smaller than Hurricane Wilma was, when Wilma was a Category 5 hurricane over the northwestern Caribbean Sea in 2005.

A Hurricane Watch is in effect for Jamaica.  A Tropical Storm Watch is in effect for the portion of the coast from the Haiti/Dominican Republic border to Port-Au-Prince, Haiti.  A Tropical Storm Warning is in effect for the portion of the coast from the Colombia/Venezuela border to Riohacha, Colombia.

Hurricane Matthew remains in a very favorable environment of minimal vertical wind shear and warm Sea Surface Temperatures.  The intensity may fluctuate as a result of eyewall replacement cycles.

A strong subtropical high is steering Hurricane Matthew toward the west.  Matthew is slowing as it approaches the western end of the subtropical high.  It will turn toward the north when it reaches the western end of that high pressure system.  However, the location, time and sharpness of the turn to the north are still uncertain.  That uncertainty means that the longer term track of Hurricane Matthew is also uncertain.  We should get more clarity about the future direction of Hurricane Matthew during the next several days.

Matthew Rapidly Intensifies Into Category 4 Hurricane

Hurricane Matthew intensified very rapidly into a Category 4 hurricane on the Saffir-Simpson Scale as it moved across the southern Caribbean Sea on Friday.  At 5:00 p.m. EDT on Friday the center of Hurricane Matthew was located at latitude 13.5°N and longitude 71.6°W which put it about 75 miles (120 km) north of Punta Gallinas, Colombia.  Matthew was moving toward the west-southwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h). and there were wind gusts t0 165 m.p.h. (265 km/h).  The minimum surface pressure was 949 mb.

The Hurricane Size Index (HII) was 28.3.  The Hurricane Intensity Index (HII) was 13.2 and the Hurricane Wind Intensity Size Index (HWISI) was 41.5.  The indices mean that Hurricane Matthew is very similar in size and intensity to what Hurricane Ike was when Ike was northeast of the Leeward Islands in 2008.  The indices also mean that Hurricane Matthew is capable of producing regional significant wind damage.

Hurricane Matthew is very well organized and it efficiently extracted energy from the warm water of the Caribbean Sea to intensify rapidly on Friday.  It has a circular eye with a diameter of about 15 miles (24 km).  The eye is surrounded by a ring of very tall thunderstorms.  The thunderstorms are pumping out large quantities of mass which allowed the surface pressure to decrease by 44 mb during the past 24 hours.  There additional bands of thunderstorms, mainly in the eastern half of the circulation.

Hurricane Matthew will remain in a very favorable environment while it is over the Caribbean Sea.  It could intensify further.  When hurricanes become as strong as Matthew strong, they sometimes undergo eyewall replacement cycles.  During an eyewall replacement cycle, a hurricane first weakens and then strengthens again when the innermost eyewall dissipates.  If eyewall replacement cycles occur in Hurricane Matthew, then the intensity will fluctuate.

A strong subtropical high pressure system north of Matthew is steering the hurricane toward the west-southwest.  That general motion is expected to continue for another 24 hours.  When Matthew reaches the western end of the subtropical high, it will start to move toward the north.  Guidance from numerical models is still divergent about the details of the turn toward the north.  If the turn is sharper, it could mean that Hurricane Matthew moves toward Haiti.  If the turn is more gradual, it could mean that Matthew heads for Jamaica and eastern Cuba.  The uncertainty is the reason why watches have been posted for both Jamaica and Haiti.

Matthew is a very powerful hurricane.  It is capable of causing regional significant wind damage.  In addition Matthew will produce very heavy rain and the potential for dangerous flash flooding.  There is also the possibility of a significant storm surge along the coast.

Matthew Becomes a Hurricane Over the Eastern Caribbean Sea

Tropical Storm Matthew strengthened into a hurricane on Thursday as it moved over the eastern Caribbean Sea.  At 8:00 p.m. EDT on Thursday the center of Hurricane Matthew was located at latitude 14.2°N and longitude 68.1°W which put it about 150 miles (240 km) north-northeast of Curacao.  Matthew was moving toward the west at 15 m.p.h. (24 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 987 mb.

Tropical Storm Watches are in effect for Curacao, Bonaire and Aruba.  The government of Columbia has also issued a Tropical Storm Watch for the portion of the coast from the Columbia/Venezuela border to Riohacha.

The structure of Hurricane Matthew became much better organized on Thursday.  A primary rainband wrapped around the center of circulation.  An eye appears to be forming.  A ring of strong thunderstorms surrounds the eye on all sides except to the south.  Additional bands of thunderstorms developed in the northern and eastern parts of the circulation.  The storms near the eye generated upper level divergence which pumped out mass to the north and east of Hurricane Matthew.  The upper level divergence pumped out enough mass to allow the minimum pressure to decrease by 17 mb during the past 24 hours.

Hurricane Matthew will be moving into an environment that will be favorable for intensification.  It will move over water where the Sea Surface Temperature is near 30°C.  An upper level trough over the western Caribbean Sea and an upper level ridge just east of Matthew are producing southwesterly winds which are blowing across the top of the hurricane.  The vertical wind shear made Hurricane Matthew’s structure asymmetrical earlier today, but the shear has been less in recent hours.  The effect of the wind shear will be to slow the rate of intensification, but it will not prevent intensification.  Hurricane Matthew will pass just north of the cost of South America and drier air could also slow the rate of intensification.

A strong subtropical high pressure system to the north of Matthew is steering the hurricane toward the west and that general motion is expected to continue for about another 48 hours.  When Hurricane Matthew reaches the western end of the ridge, it will turn toward the north.  Guidance from the numerical models continues to be quite divergent about when, where and how sharp the turn will be.  If Hurricane Matthew turns sooner and sharper, it could move over Haiti early next week.  On the other hand, if Matthew turns later and more gradually, it could affect Jamaica and eastern Cuba.  It is too early to know which scenario will eventually occur.

Hurricane Matthew could become a major hurricane over the Caribbean Sea and interests in the Greater Antilles should monitor its progress.

TD 2 Intensifies Into Tropical Storm Bonnie

Tropical Depression 2 intensified into Tropical Storm Bonnie as it passed over the warm waters of the Gulf Stream on Saturday.  At 5:00 p.m. EDT on Saturday the center of Tropical Storm Bonnie was located at latitude 31.1°N and longitude 79.4°W which put it about 120 miles (195 km) south-southeast of Charleston, South Carolina.  Bonnie was moving toward the northwest at 10 m.p.h. (16 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 1008 mb.  A Tropical Storm Warning remains in effect for the coast of South Carolina from the Savannah River to Little River Inlet.

Although the convection in Tropical Depression 2 dissipated when it passed over a region of slightly cooler Sea Surface Temperatures (SSTs) on Friday night, thunderstorms redeveloped and persisted when the system crossed the warmer SSTs in the Gulf Stream on Saturday.  Persistent thunderstorms produced enough increase in the wind speed to intensify Tropical Depression 2 into Tropical Storm Bonnie.

The circulation around Tropical Storm Bonnie is very asymmetrical.  Almost all of the thunderstorms are occurring in the northwestern quadrant of the storm and the strongest winds are being generated in that part of the circulation.  There are mainly thin bands of showers in the rest of the storm.  Winds to tropical storm force extend out about 60 miles (95 km) from the center in the northwest quadrant of Bonnie.

An upper level low over Florida and an upper level ridge over the western Atlantic Ocean are combining to generate southeasterly winds which are blowing over the top of Tropical Storm Bonnie.  Moderate vertical wind shear is contributing to the asymmetrical structure by tilting the circulation toward the northwest.  The wind shear is strong enough to inhibit intensification, but Tropical Storm Bonnie is extracting more energy as it passes over the Gulf Stream.  Bonnie could possibly intensify a little more while it is over the Gulf Stream.

The ridge east of Bonnie is steering the tropical storm toward the northwest and that general motion is expected to continue for another 12 to 24 hours.  An upper level trough approaching the ridge from west and the trough is expected to cause the ridge to weaken.  When the ridge weakens, the steering currents will also weaken.  Tropical Storm Bonnie could stall or meander for several days when that happens.

On its anticipated track the center of Tropical Storm Bonnie will approach the coast of South Carolina on Sunday.  The primary threats are coastal erosion, rip currents and locally heavy rainfall.  Persistent rain could create the potential for fresh water flooding.  Wind damage is likely to be minimal.  However, where the winds blow onshore, they could push water toward the coast and contribute to some coastal flooding.

Tropical Depression 2 Forms, Warning Issued for South Carolina

A reconnaissance plane investigated the system that was formerly designated Invest 91L on Friday afternoon and the plane found that the system had enough tropical characteristics to be classified as Tropical Depression 2 by the National Hurricane Center (NHC).  At 5:00 p.m. EDT on Friday the center of Tropical Depression 2 (TD2) was located at latitude 28.5°N and longitude 74.7°W which put it about 435 miles (695 km) southeast of Charleston, South Carolina.  TD2 was moving toward the west-northwest at 13 m.p.h. (20 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. (70 km/h).  The minimum surface pressure was 1009 mb.  A Tropical Storm Warning has been issued for the coast of South Carolina from the Savannah River to Little River Inlet.

The circulation in Tropical Depression 2 became better organized on Friday, but it would not yet be considered well organized.  More thunderstorms formed near the center of circulation and a primary rainband now curls around the the northern and western sides of the center.  However, there are only thin bands of showers in much of the eastern half of the circulation.  With persistent thunderstorms near the core of TD2, it possess enough tropical characteristics to be considered a tropical cyclone.

An upper level low near Cuba and an upper level ridge northeast of TD2 are combining to generate northerly winds over the top of the circulation.  Those winds are causing moderate vertical wind shear.  TD2 will also be moving over slightly cooler Sear Surface Temperatures (SSTs) during the next 12 to 18 hours.  The combination of the vertical wind shear and cooler SSTs could keep TD2 from intensifying much during that time period.  TD2 will move over the warmer SSTs of the Gulf Stream later on Saturday.  The vertical wind shear could also decrease somewhat.  Warmer SSTs and less wind shear could allow TD2 to intensify into Tropical Storm Bonnie later on Saturday.

A ridge northeast of TD2 is steering the tropical depression toward the west-northwest and a general motion in that direction is expected for another 36 to 48 hours.  After about two days the steering currents could weaken.  On its anticipated track TD2/Tropical Storm Bonnie is expected to approach the coast of South Carolina on Sunday.  Coastal erosion, rip currents and locally heavy rain are the primary risks.  Wind damage is likely to be minimal.

 

Invest 91L Slightly Stronger, Moving Toward U.S.

The circulation of the low pressure system designated as Invest 91L strengthened slightly on Thursday.  At 8:00 p.m. EDT on Thursday the center of Invest 91L was located at latitude 27.4°N and longitude 70.9°W which put it about 410 miles (660 km) east-northeast of Great Abaco Island, Bahamas and about 675 miles (1090 km) south-southeast of Charleston, South Carolina.  Invest 91L was moving toward the west-northwest at 10 m.p.h. (16 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to near 45 m.p.h. (70 km/h).  The minimum surface pressure was 1013 mb.  The center of Invest 91L was near NOAA buoy 41047 which reported observations consistent with those numbers.

The organization of Invest 91L improved slightly on Thursday.  A few thunderstorms formed northeast of the center of circulation and they persisted throughout the day.  However, there are few thunderstorms in other parts of Invest 91L.  The circulation became slightly more circular although it is still elongated.  The surface pressure decreased slowly, but steadily throughout the day.

The environment around Invest 91L is only marginal for intensification.  It is over water where the Sea Surface Temperature is near 26°C to 27°C.  However, an upper level low near Cuba and an upper level ridge near the east coast of the U.S. are combining to create southerly winds over the top of Invest 91L.  Those winds are causing moderate levels over vertical wind shear which is inhibiting the development of the system.  The magnitude of the wind shear decreased during the past 24 hours and it could decrease a little more on Friday as the upper level ridge moves farther east.

If more thunderstorms develop near the center of circulation, the system could be classified as a tropical depression or tropical storm.  The National Hurricane Center (NHC) is indicating that there is an 80% probability that the Invest 91L will become a tropical cyclone or subtropical cyclone within 48 hours.  NHC has tentatively tasked a reconnaissance plane to investigate the system on Friday.

The vertical wind shear is limiting the strongest part of the circulation of Invest 91L to the lower half of the troposphere.  Thus, the system is being steered toward the west-northwest by a surface pressure system over the western Atlantic Ocean.  That general motion is expected to continue with a slow northward turn.  On its anticipated track Invest 91L could approach the southeast coast of the U.S. in 48 to 72 hours.

The primary risks with Invest 91L remain coastal erosion, rip currents and locally heavy rainfall.  Some wind damage will be possible, but it is likely to be minimal.

Low Pressure Forms East of the Bahamas

A small area of low pressure developed east of the Bahamas on Wednesday afternoon and the National Hurricane Center designated the system as Invest 91L,  At 8:00 p.m. EDT on Wednesday the center of Invest 91L was located at latitude 26.6°N and longitude 67.7°W which put it about 625 miles (1005 km) east of Great Abaco Island in the Bahamas and about 895 miles (1445 km) south-southeast of Charleston, South Carolina.  Invest 91L was moving toward the north at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was he 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 1015 mb.

The circulation of Invest 91L is not well organized at the current time.  A small center of circulation was evident on late afternoon visible satellite imagery.  Several thin bands of showers are on the eastern side of the center of circulation.  However, there are very few taller thunderstorms and the circulation probably does not have a warm core at the moment.

Although Invest 91L is over water where the Sea Surface Temperature is between 26°C and 27°C, the atmospheric environment is currently unfavorable for further development.  An upper level trough near Florida is causing strong southwesterly winds to blow over the top of Invest 91L and there is significant vertical wind shear.  The wind shear is quickly dissipating any thunderstorms that start to form.  Invest 91L is forecast to move west-northwest into a more favorable environment in about a day or two.  If the system moves west, it will move into an area where the upper level winds are not as strong.  If the surface circulation is still intact at that time, less vertical wind shear could allow for the system to intensify.  The National Hurricane Center places the probability of development of a tropical cyclone or subtropical cyclone within the next five days at 60%.

Since Invest 91L primarily exists in the lower levels, it will be steered by winds in the lower troposphere.  A surface high pressure system centered off the southeast coast of the U.S. is forecast to move north of Invest 91L and the high will steer the system west-northwest toward the coast of the U.S.  On its anticipated track Invest 91L could move near the southeast coast of the U.S. during the weekend.

If Invest 91L intensifies, the highest probability is that it could become a tropical depression or tropical storm as it approaches the U.S.  It could generate coastal erosion, rip currents and locally heavy rainfall.  The threat for wind damage appears to be minimal at the current time.  People near the coast should monitor trusted sources of weather information.

Possible Development Off Southeast U.S. Coast

Even though the official start to Atlantic hurricane season is not until June 1, the atmosphere doesn’t always wait for the calendar to change to June.  Several numerical models have been predicting that a low pressure system will develop somewhere near the Bahamas later this week.  The models are also predicting that the low pressure system will move toward the southeast coast of the U.S.

A frontal boundary is over the western Atlantic Ocean.  The front runs from east of the Mid-Atlantic States to near the northern Bahamas.  Low pressure systems can develop along the southern end of frontal boundaries.  The low pressure system could start as an extratropical (non-tropical) cyclone or a subtropical (hybrid) cyclone.  The exact type of cyclone will be partly determined by the vertical wind shear later this week.  The structure of a low pressure system can change, if the environment changes and the low can be placed in a different category.

An upper level low over the western Atlantic could cause enough vertical wind shear, so that the low pressure system could be initially classified as extratropical or subtropical.  The Sea Surface Temperatures (SSTs) in the area where the low is most likely to develop are near 26° to 27°C.  There will be enough energy in the upper ocean to support the development of a tropical cyclone.  An upper level ridge could move north of the developing surface low later in the week, which could reduce the vertical wind shear.  If the shear decreases and the low pressure system extracts enough energy from the ocean to develop a warm core, it could eventually be classified as a tropical cyclone.

After the low pressure system forms, a high pressure system over the Atlantic Ocean is expected to steer the low northwest toward southeast coast of the U.S.  The low pressure system could make landfall in Georgia, South Carolina or North Carolina during the weekend or early next week.

The primary threats from the low pressure system will be coastal erosion, rip currents and potentially heavy rainfall.  The wind threat appears to be minimal, since even if the low pressure system becomes tropical, the highest probability is that it would be a tropical depression or tropical storm.

There is a great deal of uncertainty about the future of this system.  The timing of the formation of the low, the type of cyclone, the possible track of the cyclone and its intensity should become clearer later this week.  People near the southeast coast should monitor trusted sources of weather information.

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.

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.