The Tropical Disturbance we have been following is a large swirl of clouds off the east coast of Florida. Thunderstorms a trying to wrap around the center, so it is nearing tropical-depression status. The center will likely move ashore in north-central Florida late today and die out over the northern part of the state.
There is cluster of gusty downpours on the south and east side of the center of the system, but much of the circulation is covered by dry air. It’s a band of storms loosely related to an old front – from which the disturbance was born – that wraps from the Gulf across South Florida and into the disturbance that we’re interested in in the southern part of the state, however. This is the band that kicked off the downpours that moved across the southeast Florida metro areas yesterday.
The upper-level winds that have pushed the thunderstorms away from the center and dried out the circulation seem to be letting up a bit, so the disturbance is now able to wrap thunderstorms around the center and come close to meeting the organizational threshold to be designated a tropical depression. If it doesn’t hurry up, its window of opportunity will close, however, when the system moves over the landmass of Florida late in the day. If winds in those storms related to the circulation reach 40 mph, it would be designated a tropical storm.
In any case, the change of status will not affect the weather over land very much.
The focus in South Florida is the corridor of moisture, the tail, wrapping into the system, however. Wherever it’s located, the thunderstorms will be extra strong. Still, even outside of the tail, the atmosphere remains very moist over the southern part of the state, south of the old front, which means that tropical downpours will likely develop in the heating of the day. But, these are the kind of thunderstorms we’re used to.
As the center of the disturbance moves over North Florida, however, the system’s tail with embedded extra heavy thunderstorms will slowly change orientation. On Monday, it is forecast to be oriented more or less south to north over the southeast Florida metro areas. In addition, the circulation will draw in more tropical moisture.
At some point over the next day or so, that tail will pull across South Florida, and, unless we get very lucky, a period of enhance heavy rain will move though.
The steering flow in the mid and upper atmosphere is forecast to the very light over the peninsula. That means that storms that form will be slow moving, resulting in local flooding. The National Weather Service has issued a Flood Watch for the metropolitan areas of South Florida through Monday evening.
Stay alert. Be aware.
The atmosphere will stay quite moist for the next few days, but after Monday, the effects of the tropical disturbance should be past. Bands of moist and dry air are forecast to move over southern Florida later in the week, including a bit of Saharan Dust. Thunderstorms are still in the forecast each day, but they should not be as frequent or intense as those yesterday, today, and Monday.
Elsewhere, dry and dusty air continues to dominate the atmosphere across the ocean. The long-range computer forecast models don’t show anything organizing, so we continue to wait for the atmospheric shift toward more development, which usually comes around the middle of August.