[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 180839
TCDAT2

Tropical Depression Twenty-Two Discussion Number   3
NWS National Hurricane Center Miami FL       AL222020
400 AM CDT Fri Sep 18 2020

The depression is still not very well organized. It's surface wind
circulation appears to be elongated from southwest to northeast and
deep convection is mostly limited to the northeast quadrant of the
cyclone. Overnight ASCAT data and the latest TAFB Dvorak estimate
both support an intensity of 30 kt. An Air Force Reserve Hurricane
Hunter aircraft is scheduled to investigate the system later this
morning and should provide more information about the structure of
the cyclone.

Confidence in the details of the track forecast remain low at this
time. Due to the slow forward speed of the cyclone expected into
next week, small fluctuations in the depression's heading or speed
could have very large implications on any hazards experienced along
the Mexico or Texas coasts. It is critical that users not focus on
the exact forecast track, especially at days 4 and 5 when the
average NHC forecast error is about 175 and 200 miles, respectively.
My long-term motion estimate is 025/5 kt, but in reality the
depression's movement has been unsteady since it formed yesterday.
There is still good general agreement that the system will move
slowly north-northeastward for about 36 h, and then turn westward as
a ridge builds over the southeast United States. The cyclone will
then likely inch closer to the northern Mexico or southern Texas
coasts. The details of this evolution vary greatly from model to
model and the track guidance spread is higher than usual. The most
certain aspect of the forecast is that the depression will not be
moving anywhere very quickly well into next week.

Although the depression is located within an environment supportive
of intensification, only slow strengthening is likely until it gets
better organized. Beyond 72 h, the cyclone will begin to interact
with a cold front and the drier, more stable air behind it. This
should at the very least end any intensification and could lead to
weakening. Interaction with land could also cause the system to
weaken. The latest statistical intensity guidance is less
aggressive, but those models still show the system becoming a
hurricane within a couple of days, while the dynamical hurricane
models (HWRF, HMON, COAMPS-TC) do not strengthen it quite that much.
For now the NHC intensity forecast is largely unchanged and is at
the top end of the guidance envelope.

Key Messages:

1.  Tropical Depression Twenty-Two is expected to strengthen to a
tropical storm, and possibly a hurricane, while moving slowly over
the western Gulf of Mexico during the next few days.

2.  While it is too early to determine what areas could see direct
wind, storm surge, and rainfall impacts from this system, interests
throughout the western Gulf of Mexico should monitor the progress of
this system and future updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 22.9N  94.1W   30 KT  35 MPH
 12H  18/1800Z 23.7N  93.7W   35 KT  40 MPH
 24H  19/0600Z 24.9N  93.2W   45 KT  50 MPH
 36H  19/1800Z 25.7N  93.2W   50 KT  60 MPH
 48H  20/0600Z 25.9N  93.8W   60 KT  70 MPH
 60H  20/1800Z 26.0N  94.6W   65 KT  75 MPH
 72H  21/0600Z 26.3N  95.6W   65 KT  75 MPH
 96H  22/0600Z 26.7N  96.3W   60 KT  70 MPH
120H  23/0600Z 27.5N  96.0W   55 KT  65 MPH

$$
Forecaster Zelinsky
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