Hello everyone!
This is your morning briefing on Tropical Depression Nineteen which is the system in the Atlantic most likely to bring significant direct impacts to the US over the next several days. Of course there are several other systems worth watching (Paulette if you’re in Bermuda, 95L if you’re in the NE Antilles) but there’s not much new to say about those systems this morning, so they will be the subject of future updates.
One of the GOES-East instruments capable of capturing satellite imagery every 60 seconds is pointed towards TD-19 this morning which gives us a helpful look at the system’s organization. There have been several bursts of impressive deep convection associated with the system this morning, though they’ve all been south or southeast of the storm’s low-level center. How can we find the low-level center? Once the sun comes up you can use visible satellite imagery, but radar imagery and surface observations are a bit more reliable so let’s use those.
In white, I’ve highlighted some surface wind direction observations as well as the low-level swirl you’d see if you looked at a radar loop. Note that all the heavy rain (>40 dBZ) is south and east of the low-level center. While last night there was one cluster of thunderstorms making a convincing case to be the low-level center, that’s no longer the case this morning with a few different swirls drifting through the Florida Straits.
So what happens next? I see three general possibilities. The first is that deep convection redevelops over the low-level center once it moves offshore later this morning. This is pretty much the going NHC forecast, and it’s definitely possible. This would lead to TD-19 strengthening and becoming TS Sally by this afternoon. The second possibility is that the initial low-level center dies off and a new low-level center forms under one of those convective bursts to the south. This would also support strengthening later today, though it might take a little bit longer. The third possibility is that the initial low-level center remains dominant but doesn’t get any deep convection. That would lead to a much weaker system, at least for the next 12-24 hours.
Unfortunately, it’s darn near impossible to say which of these possibilities will occur. I’d put the odds somewhere near 45%-45%-10% for scenarios 1-2-3. There really isn’t much shear over the storm, and the shear that is around will be fading later today so I don’t see this vortex misalignment persisting for much more than the next 6-12 hours.
By tonight/tomorrow morning, the system will be over the Gulf of Mexico and gaining a bit of separation from Florida. It should then begin intensifying thanks to a favorable environment including very warm water, relatively low wind shear, and high mid-level moisture. If you want a more complete breakdown of TD-19’s environment, please refer to last night’s post.
This graphic shows some key information from the NHC’s 5 AM advisory along with a couple notes from me. The system did indeed job farther southwest than was originally expected, though note that this morning’s center fix is still within the cones of uncertainty from yesterday. So it’s not that big of a surprise. This has nudged the storm’s expected track a hair west over the next 24-48 hours. As a result, the system might have a little more time over water and “room to breathe” as it moves NW towards the SE LA/S MS/S AL area early next week.
The intensity forecast for the system remains mostly unchanged from last night. TD-19 should approach the coastline as a strong TS or low-end hurricane, though there’s some uncertainty regarding its exact intensity because we don’t know how quickly it will organize in the next 24 hours. I wouldn’t be surprised to see future updates show an increase in forecast intensity if the storm can consolidate today around a single low/mid level center under some persistent deep convection.
Tropical Storm watches are now posted for parts of the Florida Panhandle and will almost certainly be expanded westward towards SE LA later today. Residents in this area should be paying close attention to forecasts and should have their hurricane plans ready to implement if/when watches go up and local officials begin issuing guidance about how to prepare for the storm.
I’ll be back later today with more updates both here and on the HurricaneTrack Patreon page.
-Jack
Sillin Weather 