A large cyclonic gyre, defined by a broad area of low pressure typical of this time of the year, covers a portion of Central America and the western Caribbean Sea. This system is accompanied by an extensive area of disorganized clouds and thunderstorms, and although surface pressures are relatively low in the area, upper-level winds are currently highly unfavorable for tropical cyclone formation. Environmental conditions could become less hostile this weekend and early next week, allowing for some slow development in this region as the system drifts northwestward.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...low...30 percent.

USA National Weather Service


Jeff Masters:

A broad area of low pressure called a Central American Gyre (see tweet below) was located over the southwestern Caribbean Sea on Wednesday afternoon, and was generating disorganized heavy thunderstorms over much of the southwest and central Caribbean. This system has the potential to develop into a tropical depression early next week as it drifts slowly northward, and it will bring dangerous heavy rains to portions of Central America this week.

Satellite loops on Wednesday showed that the low, which had not yet been given an “Invest” designation, had a surface circulation that was attempting to get organized a few hundred miles south-southwest of Jamaica. The heaviest thunderstorms lay well to the east, near Hispaniola. Wind shear was a prohibitively high 30 – 40 knots, due to the presence of a strong subtropical jet stream.

The shear will relent this weekend, when the subtropical jet stream is predicted to lift to the north so that it is positioned over Cuba. This will create a region of lower wind shear over the central and western Caribbean, and recent runs of the GFS and European model have been suggesting that a tropical depression could develop early next week. This was also predicted by over 30% of the 70 ensemble members of the 0Z Wednesday GFS and European models. Any tropical cyclone that develops is likely to become entangled with an upper-level low pressure system, making the system a large and slow-to-intensify sloppy mess of a storm that will primarily be a heavy rain threat. The track such a storm might take is anyone’s guess at this point, and we’ll just have to watch how the models depict the evolution of this potential threat in coming days.

For more information, check the daily Tropical Weather Outlook, click here.