Tropical Depression Twenty-Eight Discussion Number 1 NWS National Hurricane Center Miami FL AL282020 500 PM EDT Sat Oct 24 2020
Satellite imagery and NOAA Hurricane Hunter aircraft data indicate that the broad area of low pressure that NHC has been following for the past couple of days has consolidated enough to be considered a tropical depression. GOES-16 1-minute data shows the center pretty clearly, with a new area of convection close by, and a minimum pressure of 1005 mb was reported by the aircraft in that area. The surface winds were generally fairly light within about a degree of the center, but data from the plane supports a 25-kt initial intensity.
The tropical depression hasn't been moving much, but recently it has started at least drifting toward the north-northwest. A shortwave trough moving across the southeastern United States should keep the cyclone in a rather weak steering pattern during the next day or so, with only a northwest drift anticipated. Mid-level ridging should build over the northern Gulf of Mexico on Monday, forcing the depression to move faster to the west-northwest toward the Yucatan Peninsula or Channel. The ridge shouldn't last too long, however, with a substantial upper-level low forecast to eject out of the southwestern United States in a few days, causing the tropical cyclone to sharply turn to the north and northeast on Wednesday. The guidance isn't in very good agreement, and these types of trough ejection scenarios can have significant timing differences. At this time, the NHC track forecast leans a little more on the global models than the regional hurricane models, and is just west of the model consensus.
While the large-scale shear is fairly light at the moment, the low- and mid-level circulations of the depression are not well-aligned. Thus, it might take some time for the system to strengthen despite low shear and very warm waters. In a day or two, the depression will likely have a structure that supports a faster rate of strengthening, and the intensification rate is increased while the cyclone is near the Yucatan. Although the forecast shows the system reaching hurricane strength in the southern Gulf of Mexico, this is rather uncertain given the potential land interaction and only a narrow area of favorable upper-level winds. A combination of cooler shelf waters and increasing shear will likely weaken the cyclone below hurricane strength as it approaches the northern Gulf Coast. However, strong tropical storms can still produce significant storm surge, rainfall, and wind impacts, and residents in this region will yet again need to monitor another tropical cyclone moving northward across the Gulf.
1. The depression is forecast to strengthen to a tropical storm Sunday and could bring tropical storm conditions to extreme western Cuba on Monday, where a Tropical Storm Watch is in effect. There is also a risk of tropical storm conditions in the northern Yucatan Peninsula of Mexico Monday night and Tuesday.
2. Through Wednesday, heavy rainfall is expected across portions of central and western Cuba, the Cayman Islands, Jamaica, the northeast Yucatan peninsula of Mexico, southern Florida and the Keys. This rainfall may lead to flash flooding in urban areas.
3. The system is forecast to approach the northern Gulf Coast as a tropical storm on Wednesday, and could bring storm surge, rainfall, and wind impacts to areas from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of the depression and updates to the forecast.