• Heavy Rain/Flooding So FL

    From Dumas Walker@21:1/175 to All on Sun Oct 6 10:04:00 2024
    AWUS01 KWNH 061440
    FFGMPD
    FLZ000-062030-

    Mesoscale Precipitation Discussion 1091
    NWS Weather Prediction Center College Park MD
    1039 AM EDT Sun Oct 06 2024

    Areas affected...Southern Florida Peninsula

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

    Valid 061439Z - 062030Z

    Summary...Slow moving showers and thunderstorms with high rainfall
    rates of 2 to 3 inches per hour are showing minimal movement
    across portions of South Florida. Localized rainfall totals up to
    5 inches are possible through 430 pm, and this will likely result
    in some instances of flooding.

    Discussion...Numerous showers and thunderstorms are forming near
    sea breeze boundaries and in the general proximity of a stationary
    front situated across southern Florida late this morning, and also
    ahead of a mid-level vortmax that is slowly approaching the
    southwest coast of Florida. Anomalous precipitable water values
    on the order of 2.3 to 2.6 inches are in place, per recent SPC
    mesoanalysis. Another concern is the very slow cell movements
    that have been observed by regional Doppler radar imagery over the
    past several hours, and this will likely remain the case going
    into the afternoon hours, with weak low level inflow and mean
    850-300 hPa flow. In addition, mixed layer CAPE is on the order
    of 1500-2000 J/kg, which is being aided by midday solar insolation.

    The latest CAM guidance suite depicts an increase in slow moving
    convection across the southern half of the Florida Peninsula
    through the mid-late afternoon hours, with localized rainfall
    totals on the order of 4 to 6 inches possible. Areas of the West
    Coast have picked up a few inches of rain over the past 24 hours,
    and this also holds true for areas near and to the south of Miami,
    and this will be an aggravating factor for flooding potential
    today. Hourly rain totals to 3 inches are possible, which will
    likely lead to some instances of flash flooding for urban and poor
    drainage areas.

    Hamrick

    ATTN...WFO...KEY...MFL...MLB...TBW...

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

    LAT...LON 27728071 27568016 26987993 26117990 25518007
    25088030 24818064 25048121 25608163 26128211
    26528230 26938256 27188265 27228266 27428259
    27428213 27308167 27388128
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  • From Dumas Walker@21:1/175 to All on Mon Oct 7 18:37:00 2024
    AWUS01 KWNH 072316
    FFGMPD
    FLZ000-080500-

    Mesoscale Precipitation Discussion 1094
    NWS Weather Prediction Center College Park MD
    716 PM EDT Mon Oct 07 2024

    Areas affected...southern FL into the Keys

    Concerning...Heavy rainfall...Flash flooding possible

    Valid 072314Z - 080500Z

    Summary...There is potential for a training axis of heavy rain to
    begin to impact portions of the southern FL Peninsula into the FL
    Keys by 03-06Z. Rainfall rates of 2 to 3+ in/hr will be possible,
    which may lead to flash flooding over impervious surfaces.

    Discussion...23Z surface observations, radar imagery and fading
    visible satellite imagery showed a quasi-stationary front
    extending east to west across the southern FL Peninsula with an
    apparent low on the front or at least the front aloft, located
    north of Grand Bahama Island. A secondary smaller low was noted
    just east of the Martin/Palm Beach County border, possibly
    connected to the front at the surface or just aloft.

    Low level easterly flow just north of the smaller low near the
    east coast of FL was helping to support locally heavy rain near
    and just east/offshore of Port Saint Lucie where a small bubble of
    500 J/kg MLCAPE was estimated via the 22Z SPC mesoanalysis. The
    coastal circulation may translate southward in the short term as
    the larger low to the north of Grand Bahama is forecast by short
    term RAP guidance to strengthen and become better organized
    tonight. This strengthening should result in increased northerly
    flow over the southern FL Peninsula, pushing the front southward
    toward the Middle and Upper Keys by 06Z. Farther southward
    progress of the front will likely be limited by southwesterly flow
    to the east of yet another surface low analyzed in the eastern
    Gulf near 26.4N 84.4W.

    The front is expected to act as a focus for the development of
    heavy rain where MLCAPE is forecast to be 1000+ J/kg along and
    south of the boundary, dropping off to less than 100 J/kg to the
    north. Mean steering flow should be roughly parallel to the
    boundary allowing for the repeating and training of cells, with
    rainfall rates possibly reaching 2 to 3+ in/hr within the tropical
    environment. These rates could overlap with localized urban
    centers and related impervious surfaces of the Middle/Upper Keys
    leading to localized flash flooding.

    Regarding the HRRR, while it has been fairly consistent with the
    idea of an axis of heavy rain developing in the vicinity of
    Florida Bay, the HRRR has struggled with placement of heavy rain
    from earlier today and has had differences in its forecast
    placement of the surface front and associated low pressure centers
    leading to lower confidence in its output. While the idea of
    recent HRRR cycles seems reasonable, some of its runs with 6 hr
    QPF maxima of 7 to 10 inches appears overdone.

    Otto

    ATTN...WFO...KEY...MFL...MLB...

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

    LAT...LON 27508019 27488009 27367996 27277992 27017985
    26607975 25927983 25387993 24768044 24468117
    24508196 25668170 25798099 26208030 26878038
    27248040 27418036

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