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Tropical Depression Twenty-Eight Forecast Discussion


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774 
WTNT43 KNHC 250248 CCA
TCDAT3

Tropical Depression Twenty-Eight Discussion Number   2...Corrected
NWS National Hurricane Center Miami FL       AL282020
1100 PM EDT Sat Oct 24 2020

Corrected timing in Key Message number 3

Deep convection has increased during the past few hours south of the 
estimated low-level position based on aircraft data from just after 
the release of the previous advisory. In fact, geostationary imagery 
suggests that the low-level center could be trying to reform closer 
to the deep convection. The initial intensity is set to 30 kt based 
on the latest Dvorak estimate from SAB.  Another NOAA Hurricane 
Hunter aircraft will investigate the system overnight and provide 
additional data on the cyclone's structure and intensity.

As noted above, the depression hasn't moved much, and the system 
currently appears to be stationary. Satellite imagery and upper-air 
data show a shortwave trough moving through the southeastern United 
States, which has weakened the steering flow around the cyclone. As 
the shortwave moves eastward, the subtropical ridge will expand 
westward to the north of the tropical cyclone by Monday, which 
should result in a steadier west-northeastward motion. After that 
time, a powerful mid/upper-level low is forecast to eject out of the 
southwestern U.S., which will weaken the ridge and cause the 
tropical cyclone to turn northward and northeastward as it 
approaches the northern Gulf Coast. The global models are not in 
good agreement on the details of the timing of the eastward movement 
of the upper-low. While this isn't unusual, it results in 
significant differences in when and where the tropical cyclone turns 
and exactly where it crosses the Gulf Coast next week, with model 
solutions ranging from Louisiana to the Florida Panhandle. The new 
NHC track forecast lies near the middle of the guidance envelope  
between the HCCA and the TVCA multi-model consensus. However, given 
the current lack of motion of the system and the large model spread 
late in the period, the details of the track forecast are more 
uncertain than usual. 

If the cyclone's low- and mid-level circulations can become better 
aligned, the environment for the next 2 to 3 days appears conducive 
for steady intensification, with low shear and SSTs of near 30C in 
the northwestern Caribbean and above 28C in the southern Gulf. 
After 72 hours, the shear is expected to increase while the cyclone 
moves over cooler SSTs near the northern Gulf Coast, which should 
result in weakening before the center moves inland. The new NHC 
intensity forecast is a bit higher than the previous one through 
about 60 hours, and is a blend of the latest intensity consensus 
aids and HCCA. While the current NHC forecast indicates that the 
system should weaken below hurricane strength before landfall, users 
are reminded that strong tropical storms can still produce 
significant storm surge, rainfall, and wind impacts along the 
northern Gulf Coast. The cyclone should be absorbed into a frontal 
system by the end of the forecast period.

KEY MESSAGES:

1. The depression is forecast to strengthen to a tropical storm
by Sunday and tropical storm conditions are expected in extreme 
western Cuba on Monday. Tropical storm conditions are possible in 
the northern Yucatan Peninsula of Mexico Monday night and early 
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 Florida 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 Tuesday night and 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.

FORECAST POSITIONS AND MAX WINDS

INIT  25/0300Z 18.9N  83.1W   30 KT  35 MPH
 12H  25/1200Z 19.2N  83.3W   35 KT  40 MPH
 24H  26/0000Z 20.0N  83.7W   40 KT  45 MPH
 36H  26/1200Z 20.7N  84.9W   50 KT  60 MPH
 48H  27/0000Z 21.7N  86.6W   55 KT  65 MPH
 60H  27/1200Z 23.2N  88.6W   65 KT  75 MPH
 72H  28/0000Z 25.4N  90.3W   65 KT  75 MPH
 96H  29/0000Z 31.5N  89.5W   40 KT  45 MPH...INLAND
120H  30/0000Z...ABSORBED

$$
Forecaster Brennan