Tropical Storm IDA Advisory 8月26日

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Tropical Depression Nine Discussion Number   1
NWS National Hurricane Center Miami FL       AL092021
1100 AM EDT Thu Aug 26 2021

Early morning visible satellite imagery shows that the circulation
associated with the area of low pressure over west-central
Caribbean Sea has become better defined. There has also been an
increase in the organization of the associated convective activity,
and based on consensus Dvorak T-numbers of 2.0 from TAFB and SAB,
advisories are being initiated on a tropical depression. The initial
intensity is set at 30 kt, in agreement with the subjective
satellite estimates.  The official reporting station in Kingston,
Jamaica, has reported sustained winds of 25 kt with gusts to 35 kt
during the past couple of hours. An Air Force Reserve
reconnaissance aircraft is scheduled to be in the system later this
afternoon to provide more information on the system's structure
and intensity.

The depression is moving northwestward or 325/11 kt, however the
initial motion is a bit more uncertain than normal since the low-
level center has only recently formed.  The cyclone is forecast
to move steadily northwestward around the southwestern portion of a
deep-layer ridge centered over the western Atlantic.  This track
should bring the center near or over western Cuba late Friday,
over the southeastern and central Gulf of Mexico Friday night and
Saturday, and have the center approach the northern Gulf coast on
Sunday.  The track guidance is in relatively good agreement, however
the average NHC track forecast error at day 4 is around 175 miles,
so users should not focus on the details of the long range track
forecast. Some shifts in the track are likely until the system
consolidates and becomes better defined. The NHC track is near the
various consensus model aids and is in best agreement with the GFS
ensemble mean.

The depression will be moving over the high ocean heat content
waters of the northwestern Caribbean Sea during the next 24-36
hours.  This, in combination with low vertical wind shear and a
moist environment, should allow for steady strengthening.  The
depression is forecast to become a tropical storm later today or
tonight, and could approach hurricane strength as it passes near
or over western Cuba.  Once the system moves into the Gulf of
Mexico, conditions are expected to be conducive for additional
strengthening, and rapid intensification is explicitly shown in
the NHC forecast between 48 and 72 hours. The NHC intensity forecast
brings the system near major hurricane strength when it approaches
the northern Gulf coast on Sunday. This forecast is supported by the
HWRF and CTCI models, and the GFS, ECMWF, and UKMET global model
guidance, which all significantly deepen the cyclone over the Gulf
of Mexico.  As a result, there is higher-than-normal confidence
that a strengthening tropical cyclone will be moving over the Gulf
this weekend.

Key Messages:

1. Tropical storm conditions are likely in portions of the Cayman
Islands tonight and western Cuba Friday and Friday night, with
dangerous storm surge possible in portions of western Cuba,
including the Isle of Youth, in areas of onshore flow.

2. The system is expected to produce life-threatening heavy rains,
flash flooding and mudslides across Jamaica, the Cayman Islands,
western Cuba, including the Isle of Youth and northeastern portions
of the Yucatan Peninsula.

3. This system is forecast to approach the northern Gulf Coast at or
near major hurricane intensity on Sunday, although the forecast
uncertainty is larger than usual since the system is just forming.
There is a risk of life-threatening storm surge, damaging
hurricane-force winds, and heavy rainfall Sunday and Monday along
the northern Gulf Coast from the Florida Panhandle to the upper
Texas coast, with the greatest risk along the coast of Louisiana.
Interests in these areas should closely monitor the progress of this
system and ensure they have their hurricane plan in place.

FORECAST POSITIONS AND MAX WINDS

INIT  26/1500Z 16.9N  79.2W   30 KT  35 MPH
 12H  27/0000Z 18.2N  80.4W   35 KT  40 MPH
 24H  27/1200Z 20.3N  82.0W   45 KT  50 MPH
 36H  28/0000Z 22.5N  83.9W   55 KT  65 MPH...INLAND
 48H  28/1200Z 24.4N  86.0W   65 KT  75 MPH...OVER WATER
 60H  29/0000Z 26.1N  88.1W   80 KT  90 MPH
 72H  29/1200Z 27.7N  90.0W   95 KT 110 MPH
 96H  30/1200Z 30.5N  92.0W   70 KT  80 MPH...INLAND
120H  31/1200Z 33.7N  91.2W   30 KT  35 MPH...INLAND

$$
Forecaster Brown