The National Hurricane Center announced that Tropical Depression Eighteen has formed over the northwestern Caribbean Sea just south of Isla de Juventud in Cuba. The formation of TD Eighteen has implications on the forecast for Sunday’s storm as a complex scenario is set to unfold.

Impacts: forecasters are anticipating a high wind, and heavy rain event coming up. Storm total rainfall of 2-4″ and possibly higher could lead to urban and small stream flooding. The amount of rainfall over a short period of time has led our local forecast office to issue flash flood watches for much of the region. Winds will pick up as well, backing from the south to southeast, east, and eventually to north and northwest. Wind gusts could become a problem for local airports and for poor travel conditions in general. Thunderstorms are a possibility as well.

Timing: Winds are already increase today, and cloud cover will do so as well as the day progresses. Chances for rain will increase in the overnight hours, probably after 2-3AM. The strongest wind gusts will actually come on the back side of the storm going into Monday as it intensifies and the pressure gradient increases.

Discussion: a complicated set up is unfolding with a longwave trough (on the left) draping from the Great Lakes into the Gulf of Meixco interacting with a developing closed low over the Tennessee Valley, and TD Eighteen. TD Eighteen is likely to strengthen into a tropical storm, which would be named Phillippe if it did form. The effect of this will be to provide a conveyor of warm and moist air from the tropics up to our area. This will help feed the developing non-tropical low forming over the southeast. This low will become the primary rainmaker, and the tropical system (whether a depression or storm) will eventually merge with it. Plenty of instability to fuel a growing storm! The pressure gradient will tighten as this storm strengthens and departs eastward, and that will be the reason for a gusty start to the work week.