• STRMDISC: TS Gamma 8

    From Weather Alert@21:1/175 to All on Sun Oct 4 14:03:00 2020
    719
    WTNT45 KNHC 040855
    TCDAT5

    Tropical Storm Gamma Discussion Number 8
    NWS National Hurricane Center Miami FL AL252020
    400 AM CDT Sun Oct 04 2020

    Tropical Storm Gamma has moved back over open water, just offshore
    the northern Yucatan Peninsula in the extreme southern Gulf of
    Mexico. Although deep convection has been increasing near the
    center, the overall convective cloud shield is now strung out to
    the north and northeast due to southerly to southwesterly vertical
    wind shear in excess of 15 kt. The initial intensity of 45 kt is
    based on an earlier ASCAT pass showing 39-kt surface winds just
    offshore the northeastern tip of Yucatan, and these winds were
    likely under-sampled due to their proximity to the coast. Satellite classifications from both TAFB and SAB were T3.0/45 kt, which
    further supports the 45-kt intensity assessment.

    The initial motion estimate is 355/04 kt. As the day progresses,
    Gamma is expected to move further into a slight weakness in
    subtropical ridge located to the north of the cyclone and slow down,
    possibly stalling by this afternoon. The trough over the
    southeastern U.S. that is creating the weakness is forecast to move
    offshore the U.S. east coast by tonight, causing the ridge to build
    back in and force Gamma westward to west-southwestward from Monday
    through Thursday. The new NHC track forecast follows the TVCA and
    FSSE consensus models, and is similar to but slightly slower and a
    little to the right/north of the previous advisory track.

    Now that Gamma is back out over open water, some slight
    re-strengthening is expected today. However, strong southerly
    vertical wind shear is forecast to increase across the cyclone by
    tonight and especially on Monday, and continue for the next few
    days. The result should be a slow but gradual weakening trend on
    Monday through the end of the forecast period. The new official
    intensity forecast follow the downward trend of the simple- and corrected-consensus models, but is slightly higher than the IVCN,
    HCCA, FSSE intensity models.

    KEY MESSAGES:

    1. Gamma is expected to produce heavy rainfall for several days over
    portions of southeastern Mexico, the Yucatan Peninsula, Central
    America, and far western Cuba. This rainfall could result in
    life-threatening flash flooding and mudslides, particularly in the
    mountainous regions of southeastern Mexico and Central America.

    2. Even though Gamma is offshore, tropical storm conditions will
    continue across portions of the Yucatan Peninsula today.


    FORECAST POSITIONS AND MAX WINDS

    INIT 04/0900Z 22.0N 88.2W 45 KT 50 MPH
    12H 04/1800Z 22.6N 88.3W 50 KT 60 MPH
    24H 05/0600Z 22.7N 88.6W 45 KT 50 MPH
    36H 05/1800Z 22.4N 89.4W 45 KT 50 MPH
    48H 06/0600Z 22.0N 90.2W 40 KT 45 MPH
    60H 06/1800Z 21.5N 90.9W 40 KT 45 MPH
    72H 07/0600Z 21.0N 91.6W 40 KT 45 MPH
    96H 08/0600Z 20.4N 92.5W 40 KT 45 MPH
    120H 09/0600Z 20.4N 93.4W 40 KT 45 MPH

    $$
    Forecaster Stewart
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