Tropical Storm ZETA Advisory 10月25日

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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.

KEY MESSAGES:

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.

FORECAST POSITIONS AND MAX WINDS

INIT  24/2100Z 18.7N  83.0W   25 KT  30 MPH
 12H  25/0600Z 19.0N  83.2W   30 KT  35 MPH
 24H  25/1800Z 19.5N  83.5W   35 KT  40 MPH
 36H  26/0600Z 20.1N  84.2W   40 KT  45 MPH
 48H  26/1800Z 20.9N  85.6W   45 KT  50 MPH
 60H  27/0600Z 22.0N  87.5W   55 KT  65 MPH
 72H  27/1800Z 23.4N  89.4W   65 KT  75 MPH
 96H  28/1800Z 27.5N  91.0W   55 KT  65 MPH
120H  29/1800Z 35.5N  84.5W   25 KT  30 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake