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.