For now, 99-L can be seen on radar from MeteoFrance moving through the Leeward Islands.
A Hurricane Hunters reconnaissance mission will investigate 99-L late this morning. Tuesday, another separate mission was unable to find a tight, consolidated surface low-pressure center that would have prompted the initiation of advisories for Tropical Depression Eight.
One factor that may be holding the further consolidation of convection into a surface low-pressure center is some wind shear, namely, the change in wind speed and/or direction with height, north of 99-L.
Current Satellite, Wind Shear
The analysis above shows areas of stronger wind shear in the purple contours. Wind shear is generally hostile to developing or mature tropical cyclones.
Wind shear tends to inhibit the development of tropical cyclones by blowing the convection away from any area of low pressure trying to form.
Regardless of development, this tropical wave will have one primary impact in its brush with the Caribbean basin, locally heavy rainfall.
The National Weather Service has issued a flash flood watch for Puerto Rico and the U.S. Virgin Islands. Rainfall totals of 2-4 inches (locally higher) are expected through Wednesday night in those areas.
Caribbean Rainfall Forecast Through Friday
The National Hurricane Center says this system has a medium to high chance of development into a tropical depression or tropical storm over the next 2 to 5 days.
A tight consensus of our guidance suggests the disturbance should continue in a general west or west-northwest trajectory the next several days.
The Weather Channel