Tag Archives: Windward Islands

Tropical Storm Matthew Develops Near the Windward Islands

The National Hurricane Center determined that a surface circulation center formed within Invest 97L on Wednesday morning and it designated the system as Tropical Storm Matthew.  At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Matthew as located at latitude 13.4°N and longitude 60.7°W which put it about 35 miles (55 km) southeast of St. Lucia.  Matthew was moving toward the west at 21 m.p.h. (33 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 1008 mb.

Tropical Storm Warnings have been issued for Guadeloupe, Martinique, Barbados, Dominica, St. Lucia, and St. Vincent and the Grenadines.

The circulation of Tropical Storm Matthew is still organizing and it appears as if the surface center is located southwest of the mid-level center.  There are many more thunderstorms north and east of the center and there are fewer thunderstorms south and west of the center.  The strongest winds are occurring in the bands of thunderstorms northeast of the center of circulation.  The winds are much weaker in the western half of Tropical Storm Matthew.  The stronger thunderstorms northeast of the center of circulation are generating upper level divergence which is pumping mass out to the north and east of Matthew.

Tropical Storm Matthew will be moving into an environment that is favorable for intensification The Sea Surface Temperatures in the eastern and central Caribbean Sea are near 30°C.  The upper level winds are weak and there is not much vertical wind shear.  Even with those favorable conditions, several factors could slow the rate at which Tropical Storm Matthew intensifies.  First, it is moving west at 21 m.p.h. (33 km/h).  Sometimes tropical cyclones generate low level vertical wind shear when they move that quickly.  Second, the asymmetrical distribution of thunderstorms around the circulation of Matthew could prevent the tropical storm form efficiently using the energy it extracts from the ocean.  In addition, if Tropical Storm Matthew moves too close to the northern coast of South America, it could pull in some drier air, which would also slow the rate of intensification.  Even with those potential inhibiting factors, Tropical Storm Matthew is likely to become a hurricane by the end of the week and it could become a major hurricane while it is over the Caribbean Sea.

A subtropical high pressure system to the north of Matthew is steering the tropical storm toward the west and that general motion is expected to continue for several more days.  Tropical Storm Matthew is likely to slow down over the weekend as it gets closer to the western end of the subtropical high.  Matthew will likely turn toward the north during the weekend.  There is a great deal of variability in how quickly and sharply the models predict the turn will be.  Some models forecast a quick sharp turn toward the north that could eventually carry Matthew near Bermuda.  Other models forecast a later slower turn that occurs over the western Caribbean Sea and could take take Matthew closer to the U.S.  It is too early to know which scenario will be the right one.

Tropical Storm Matthew will bring gusty winds and locally heavy rain to the Windward Islands and southern Leeward Islands.  Interests in other parts of the Caribbean Sea, the Bahamas, U.S. and Bermuda should monitor the progress of Tropical Storm Matthew.

Tropical Depression Six Forms Over Eastern Atlantic

A center of circulation developed within a tropical wave designated as Invest 98L on Tuesday and the National Hurricane Center classified the system as Tropical Depression Six.  At 11:00 p.m. EDT on Tuesday the center of Tropical Depression Six was located at latitude 12.6°N and longitude 34.1°W which put it about 1800 miles (2900 km) east of the Leeward Islands.  The depression 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. (70 km/h).  The minimum surface pressure was 1008 mb.

The circulation of Tropical Depression Six is still organizing.  A center of circulation exists near the surface and thunderstorms are developing near the center.  Several partial spiral bands are beginning to form.  The thunderstorms near the center are generating a small region of upper level divergence, but the divergence is occurring mainly to the southwest of the depression.

Tropical Depression Six is moving through an environment that favors intensification.  It is moving over water where the Sea Surface Temperature is near 27°C.  An upper level ridge to the north is causing northeasterly winds to blow across the top of the depression.  There is some vertical wind shear, but the shear will only slow the rate of intensification.  The shear is not strong enough to prevent intensification and Tropical Depression Six is expected to become a tropical storm during the next day or two.

The subtropical ridge over Africa and the Atlantic Ocean is splitting into two parts and Tropical Depression Six is moving toward the northwest into the split that is developing.  The depression is expected to continue to move toward the northwest in the short term.  The longer term motion will depend on how strong Tropical Depression Six becomes.  If it intensifies more and develops a taller circulation, then the depression will be steered by the winds higher in the atmosphere.  The winds at those levels are more likely to carry it into the central Atlantic Ocean.  However, if vertical wind shear weakens the depression and the circulation is shallower, then the winds in the lower levels of the atmosphere could carry the depression farther to the west.  In either case Tropical Depression Six is no immediate threat to any land area.

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.

Tropical Depression 4 Forms over Eastern Atlantic

As the calendar reaches mid-August, the environment over the tropical Atlantic Ocean typically becomes more favorable for tropical cyclone formation.  The Sea Surface Temperature warms and vertical wind shear decreases.  Despite the ongoing El Nino in the tropical Pacific Ocean, we are seeing the typical pattern develop in the Atlantic for this time of year.  A low level circulation within an area of thunderstorms over the eastern Atlantic Ocean became better organized on Tuesday and the National Hurricane Center classified the system as Tropical Depression Four (TD4).  At 11:00 a.m. EDT on Tuesday the enter of Tropical Depression Four was located at latitude 10.6°N and longitude 36.5°W which put it about 1665 miles (2765 km) east of the Windward Islands.  TD4 was moving toward the west at 13 m.p.h. (20 km/h).  The maximum sustained wind speed was 35 m.p.. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1009 mb.

TD4 is currently in an environment that is favorable for intensification.  The upper level winds are light and the thunderstorms are generating upper level divergence in all directions.  It is currently over water where the Sea Surface Temperature is near 28°C.  As long as TD4 moves westward, it will stay over warmer water and intensification will be likely.  If TD4 were to move more toward the northwest, then it would move over slightly cooler water and less intensification would occur.  Since TD4 is forecast to move west, it is expected to become Tropical Storm Danny, and it could be a hurricane later this week.

A subtropical ridge north of TD4 is steering it toward the west and that steering motion is expected to continue for the next 24 to 48 hours.  Later this week an upper level trough passing north of the ridge is expected to weaken the ridge, which could cause TD4 to move northwesterly for a day or so.  After the upper level trough moves off to the east, the subtropical ridge is forecast to steer TD4 back more toward the west.  On its anticipated track TD4 is expected to be east of the Windward Islands this weekend.