• STRMDISC: Sally 14

    From Dumas Walker@21:1/175 to All on Mon Sep 14 23:25:00 2020
    794
    WTNT44 KNHC 142045
    TCDAT4

    Hurricane Sally Discussion Number 14
    NWS National Hurricane Center Miami FL AL192020
    400 PM CDT Mon Sep 14 2020

    After the rapid spin up of the inner core late this morning, the
    most recent aircraft passes through the center have not found any
    higher flight-level winds, however there have been a few SFMR winds
    of 85-90 kt reported. Using a blend of the flight-level and SFMR
    winds the initial intensity has been increased to 85 kt for this
    advisory. The next Air Force and NOAA aircraft have begun to sample
    the storm. Now that Sally has developed an inner core, the
    favorable atmospheric and ocean conditions of low vertical wind
    shear and warm water should allow for additional strengthening
    tonight while the system moves over the north-central Gulf of
    Mexico, and Sally could approach major hurricane strength. On
    Tuesday, the global models are predicting an increasing in
    southwesterly flow aloft, and this increase in shear, the potential
    for land interaction, and some upwelling over the shallower shelf
    waters over the northern Gulf should slow the intensification
    process. The NHC intensity forecast is again near the upper-end of
    the guidance envelope in best agreement with the HWRF and HFIP
    corrected consensus models.

    Sally did not move much earlier today as the center re-formation
    took place, but it appears that a slow west-northwestward to
    northwestward motion has resumed. Weak ridging over the
    southeastern United States is expected to steer Sally generally west-northwestward through early Tuesday. After that time, steering
    currents weaken and a slow northward motion is forecast as a weak
    mid-level trough develops over the the central United States. This
    trough is forecast to slide eastward, allowing Sally to begin a
    slow north-northeastward or northeastward motion. The specific
    timing and location of the turn will be critical as to the eventual
    location and timing of landfall along the north-central Gulf Coast.
    The UKMET and ECMWF models show a more northeastward motion after
    the turn and have trended eastward, with the ECMWF much slower than
    the remainder of the guidance. The NHC track has been adjusted
    eastward, and this requires and eastward extension of the hurricane
    warning. The new track most closely follows the GFS and it ensemble
    mean, but lies to the west of the various consensus aids, so some
    additional eastward adjustments could be needed in subsequent
    advisories.

    Given the uncertainty in the timing and location of the northward
    turn and the lack of well-defined steering currents, users are
    reminded to not focus on the exact forecast track or the specific
    timing and location of landfall. Hurricane-force winds, dangerous
    storm surge, and flooding rainfall will affect a large portion of
    the north-central Gulf Coast during the next few days.

    KEY MESSAGES:

    1. It is too early to determine where Sally's center will move
    onshore given the uncertainty in the timing and location of Sally's
    northward turn near the central Gulf Coast. Users should not focus
    on the details of the official forecast track, since NHC's average
    forecast error at 36 to 48 hours is around 60 to 80 miles, and
    dangerous storm surge, rainfall, and wind hazards will extend well
    away from the center.

    2. An extremely dangerous and life-threatening storm surge is
    expected for areas outside the southeastern Louisiana Hurricane and
    Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to
    the Okaloosa/Walton County Line in the Florida Panhandle, where a
    Storm Surge Warning is in effect. Residents in these areas should
    follow any advice given by local officials.

    3. Hurricane conditions are expected late tonight or early Tuesday
    within the Hurricane Warning area in southeastern Louisiana and are
    expected by late Tuesday and Tuesday night within the Hurricane
    Warning area along the Mississippi and Alabama coastlines and the
    western Florida Panhandle. Tropical storm conditions are likely to
    begin this evening in these areas and preparations should be rushed
    to completion.

    4. Life-threatening flash flooding is likely, as well as widespread
    minor to isolated major flooding, on area rivers along and just
    inland of the Central Gulf Coast. Significant flash and urban
    flooding, as well as widespread minor to moderate river flooding is
    likely across Mississippi and Alabama through the middle of the
    week. Flooding impacts are expected to spread farther across the
    Southeast through the week. Sally could continue to produce flash
    flooding across the Florida peninsula and prolong existing minor
    river flooding across west-central Florida through today.

    FORECAST POSITIONS AND MAX WINDS

    INIT 14/2100Z 28.8N 87.4W 85 KT 100 MPH
    12H 15/0600Z 29.2N 88.2W 95 KT 110 MPH
    24H 15/1800Z 29.7N 88.7W 95 KT 110 MPH
    36H 16/0600Z 30.4N 88.6W 90 KT 105 MPH...INLAND
    48H 16/1800Z 31.3N 88.0W 55 KT 65 MPH...INLAND
    60H 17/0600Z 32.2N 86.8W 30 KT 35 MPH...INLAND
    72H 17/1800Z 32.9N 85.5W 25 KT 30 MPH...INLAND
    96H 18/1800Z 33.5N 83.0W 20 KT 25 MPH...POST-TROP/REMNT LOW
    120H 19/1800Z...DISSIPATED

    $$
    Forecaster Brown
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