• Heavy Rain/Flooding FL/GA

    From Dumas Walker@21:1/175 to All on Wed Sep 25 20:26:00 2024
    AWUS01 KWNH 252247
    FFGMPD
    FLZ000-GAZ000-ALZ000-260445-

    Mesoscale Precipitation Discussion 1058
    NWS Weather Prediction Center College Park MD
    646 PM EDT Wed Sep 25 2024

    Areas affected...Florida Panhandle into Central Georgia

    Concerning...Heavy rainfall...Flash flooding likely

    Valid 252245Z - 260445Z

    SUMMARY...Particularly heavy rain is expected in southwest Georgia
    into the Florida Panhandle this evening due to convergence of
    pre-frontal activity from the west and the outermost banding of
    Helene from the south. Flash flooding is likely despite dry
    preconditions due to extreme rainfall rates of 3" per hour.

    DISCUSSION...Heavy and locally excessive pre-frontal activity over
    southeast AL and west-central GA is shifting east on outflow while
    the outermost bands of Helene have been tracking north over the FL
    Peninsula. Convergence of these two areas is progged this evening
    over southwest Georgia into the FL Big Bend/eastern Panhandle.
    This outer band is on the leading edge of particularly high
    moisture, lining up with the 2.2" PW contour from recent RAP
    analysis with PW climbing to 2.4" farther down the Peninsula which
    is 2.5 sigma over normal. Sufficient instability is present with
    MLCAPE of 1000 to 1500 J/kg.

    Recent HRRR runs have been under realizing rainfall rates which
    are estimated from KTLH and KVAX over Thomas County, GA. However,
    the timing in recent HRRRs has been decent with the main
    convergence over southwest GA occurring between 00Z and 02Z. There
    is a risk for 2 to 5" rainfall through the rest of the evening
    which is only a little above the high 3hr FFG of 4 to 5" due to a
    lack of rain in this part of GA yet. However, these extreme rates
    from slow moving and merging cells warrants likely wording for
    this discussion.

    A trough extending southwest from western GA extends over the FL
    Panhandle and should provide a focus for some additional heavy
    rain, so the discussion area is extended west about halfway
    through the Panhandle. As of now the area west of Apalachee Bay
    which received heavy rain earlier today appears to be south of the
    main heavy rain risk area, but given this coast is in the main
    Helene moisture plume there is at least a localized excessive
    rainfall risk there.

    Further banding from Helene approaches this area overnight, so
    expect further MPDs tonight and through the passage of Helene
    Thursday night.

    Jackson

    ATTN...WFO...BMX...FFC...JAX...MOB...TAE...

    ATTN...RFC...SERFC...NWC...

    LAT...LON 33338324 32558294 30998309 30018392 29348506
    30198636 30938639 31758554 32598502 33278448

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