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.