The National Hurricane Center (NHC) was monitoring two areas for possible tropical development on Thursday afternoon. A strong tropical wave was moving through the southeastern Caribbean Sea and the wave was designated as Invest 90L. At 2:00 p.m. EDT on Thursday the center of Invest 90L was located at latitude 12.2°N and longitude 65.8°W which put it about 160 miles (260 km) east of Bonaire. The tropical wave was moving toward the west at 18 m.p.h. (29 km/h). The maximum sustained wind speed was 35 m.p.h. (55km/h) and there were gusts to 45 m.p.h. (75 km/h). The minimum surface pressure was 1011 mb.
Another tropical wave moved off the coast of West Africa on Thursday and NHC designated that wave as Invest 99L. At 2:00 p.m. EDT on Thursday the center of Invest 99L was located at latitude 10.2°N and longitude 20.9°W which put it about 370 miles (595 km) south-southeast of the Cabo Verde Islands. The tropical wave was moving toward the west at 18 m.p.h. (29 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1010 mb.
The tropical wave over the southeastern Caribbean Sea will have the most immediate impact to land. The wave could bring gusty winds to Aruba, Bonaire and Curacao within 24 hours. The circulation of Invest 90L is elongated in an east-west direction and that is probably because of strong easterly winds blowing in the lower atmosphere. There are some indications of a counterclockwise rotation on loops of visible satellite imagery, but it is not clear if the rotation extends all the way down to the surface. The tropical wave is generating winds to near tropical storm force in the northern portion of the wave. There are numerous thunderstorms developing along the axis of the wave.
Invest 90L is moving under the western end of an upper level ridge. The ridge is producing southerly winds which are blowing over the top of the tropical wave and those winds are contributing to moderate vertical wind shear. The strong easterly winds in the lower levels are also contributing to the shear. Invest 90L could develop into a tropical cyclone when it moves farther west. The shear could diminish and the Sea Surface Temperatures in the western Caribbean Sea and Bay of Campeche are very warm. NHC is indicating that there is a 20% probability Invest 90L will become a tropical cyclone during the next five days.
The tropical wave over the far eastern Atlantic has a better chance of developing into a tropical cyclone. Invest 99L is moving over water where the Sea Surface Temperature is near 28°C. It is moving under the eastern end of an upper level ridge. The ridge is causing northeasterly winds which are blowing toward the top of the tropical wave. Those winds are producing moderate vertical wind shear. When the wave moves farther west, it will move under weaker winds and the wind shear will decrease. NHC is indicating that there is a 70% probability that Invest 99L will become a tropical cyclone during the next five days.
An Air Force Reserve Hurricane Hunter aircraft investigated Potential Tropical Cyclone 02 on Monday afternoon as it moved closer to Trinidad and the plane found a closed circulation. Based on data from the reconnaissance plane the National Hurricane Center classified the system as Tropical Storm Bret. At 8:00 p.m. EDT on Monday the center of Tropical Storm Bret was located at latitude 9.5°N and longitude 60.5°W which put it about 85 miles (135 km) southeast of Trinidad. Bret was moving toward the west-northwest at 25 m.p.h. (40 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.
Tropical Storm Warnings are in effect for Grenada, Trinidad, Tobago and the coast of Venezuela from Pedernales to Cumana. Tropical Storm Watches have been issued for Aruba, Bonaire, and Curacao.
The reconnaissance plane found a well organized center of circulation at the surface. The strongest winds were occurring in vigorous bands of thunderstorms located north of the center of circulation. Weaker showers and thunderstorms were occurring in bands south of the center of circulation. The thunderstorms north of the center were generating upper level divergence which was pumping mass away to the north of the tropical storm. The circulation of Tropical Storm Bret is fairly small. Winds to tropical storm force only extend out about 80 miles (130 km) to the north of the center of circulation.
Tropical Storm Bret will move through an environment that will only be marginally favorable for intensification on Tuesday. Bret will move over water where the Sea Surface Temperature is near 29°C. An upper level ridge east of Bret and an upper level trough to the west are producing southerly winds which are generating moderate vertical wind shear. The vertical wind shear may be responsible for the asymmetrical distribution of thunderstorms. The shear will also inhibit intensification during the next 24 hours, although some intensification may possible. When Bret moves into the Caribbean Sea, the vertical wind shear will increase. Tropical Storm Bret will also move very close to the north coast of Venezuela. It could pull drier air from South America into the southern part of the circulation, which would contribute to further weakening.
The subtropical high pressure system over the Atlantic Ocean is steering Tropical Storm Bret rapidly toward the west-northwest. A fast west-northwesterly motion is forecast to continue for several more days. On its anticipated track Tropical Storm Bret will move across Trinidad, near the north coast of Venezuela and toward Aruba, Bonaire, and Curacao. It will bring gusty winds and locally heavy rain to all of those places.
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.