[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 181449
TCDAT2

Tropical Depression Twenty-Two Discussion Number   4
NWS National Hurricane Center Miami FL       AL222020
1000 AM CDT Fri Sep 18 2020

Satellite imagery indicates that Tropical Depression Twenty-Two is
getting better organized, with gradually increasing convective
banding in the northeastern semicircle.  Satellite intensity
estimates include 35 kt from TAFB, 30 kt from SAB, and 35 kt from
CIMSS satellite consensus, which means the depression is close to
tropical-storm strength.  Given the lack of organization seen in
earlier scatterometer data, the intensity will be held at 30 kt
pending the data from the next set of scatterometer overpasses.  It
should be noted that the Air Force Reserve Hurricane Hunter
aircraft that was scheduled to investigate the depression had to
turn back after getting hit by lightning.

The initial motion is a somewhat uncertain 015/6.  For the next
24 h or so, the cyclone should move north-northeastward as it is
steered by a mid- to upper-level trough over Texas and northeastern
Mexico.  This trough is then expected to lift out to the northeast,
with low- to mid-level ridging building to the north of the
cyclone.  This should cause a westward turn at a continued slow
forward speed.  Near the end of the forecast period, a mid-latitude
trough over the central United States should cause the ridge to
weaken and steer the cyclone northward to northeastward near the
Texas coast.  While the guidance agrees with this general sense of
the motion, there are a lot of differences in the models on the
when's and where's of the various turns.  Therefore, 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.

The depression is currently in an environment of light to moderate
southwesterly shear, and the global models suggest that this will
generally continue through the forecast period.  This, combined
with forecast dry air entrainment near the 72 h point, has resulted
in the intensity guidance keeping the system near to below
hurricane strength through the forecast period.  The new intensity
forecast is changed little from the previous one and calls for
the cyclone to be at hurricane strength at 60 and 72 h.  However,
this part of the forecast lies at the upper edge of the intensity
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. There is an increasing risk of heavy rainfall and flooding along
the Texas coast from Sunday through at least the middle of next
week as the system is forecast to move slowly near the Texas coast.
For additional information, see products from your local National
Weather Service office.

3.  While it is too early to determine what areas could see direct
wind and storm surge 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  18/1500Z 23.8N  93.9W   30 KT  35 MPH
 12H  19/0000Z 24.8N  93.6W   35 KT  40 MPH
 24H  19/1200Z 25.9N  93.4W   45 KT  50 MPH
 36H  20/0000Z 26.3N  93.8W   50 KT  60 MPH
 48H  20/1200Z 26.5N  94.6W   60 KT  70 MPH
 60H  21/0000Z 26.6N  95.6W   65 KT  75 MPH
 72H  21/1200Z 26.9N  96.2W   65 KT  75 MPH
 96H  22/1200Z 27.5N  96.5W   60 KT  70 MPH
120H  23/1200Z 28.5N  95.5W   55 KT  65 MPH

$$
Forecaster Beven
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