• STRMDISC: Tropical Storm Melissa Discussion Number 6

    From COD Weather Processor@1:2320/105 to wx-atlan@lists.illinois.edu on Wed Oct 22 20:42:47 2025
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    WTNT43 KNHC 222042
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    Tropical Storm Melissa Discussion Number 6
    NWS National Hurricane Center Miami FL AL132025
    500 PM EDT Wed Oct 22 2025

    Like yesterday, Melissa's structure has come unglued this
    afternoon, with the low-level circulation becoming exposed to
    the west of the bursting deep convection. While that convection
    continues to have very cold cloud tops, it lacks much organization,
    remaining parked down-shear of the storm with 20-30 kt of
    west-northwesterly shear undercutting the outflow layer. This
    disjointed structure is nicely exhibited on an 1825 UTC AMSR2 pass.
    While the objective intensity estimates in general are a little
    higher than this morning, the subjective Dvorak estimates are lower,
    and given the disjointed structure of Melissa, it favors holding the
    intensity at 45 kt this advisory. Another Air Force Reserve and the
    first NOAA Hurricane Hunter mission will be in the storm this
    evening to provide more structural information.

    Melissa has taken a short-term jog westward as it became exposed,
    but now appears to be resuming a very slow west-northwestward motion
    at 290/2 kt. The track reasoning remains similar to the previous
    forecast over the next 2-3 days, with the forecast storm structure
    likely to have a significant role in the future track. Dynamical
    models that show the storm becoming more vertically aligned and deep
    (GFS, HWRF) show Melissa turning north or northeastward due to
    westerly deep-layer steering into a weakness induced by a broad
    upper-level trough located over the Bahamas. However, models that
    show Melissa remaining more shallow and misaligned (ECMWF, HAFS-A/B)
    maintain a northwestward or north-northwestward component of
    motion. Compared to this morning, the track guidance has shifted
    slower and farther west, possibly due to the farther west initial
    position. The NHC track has been shifted westward and is also a
    little southward after 60 h, but remains farther north and east of
    the ECMWF and HAFS models this cycle, and is roughly in between the
    HFIP consensus approach (HCCA) and Google DeepMind ensemble mean
    (GDMI). This track forecast favors the models that keep Melissa weak
    and less prone to the deep-layer steering over the next 24-48 hours.
    However, this remains a low confidence track forecast other than
    Melissa maintaining a slow motion for the majority of the period.

    The current vortex misalignment of Melissa is a significant
    impediment to short-term intensification, and the vertical wind
    shear is expected to maintain this tilted structure over the next
    24-36 hours, although I can't preclude any center reformations
    down-shear, like what occurred last night. After this period, the
    ECWMF-SHIPS guidance now indicates the ongoing westerly shear will
    decrease to 10-15 knots, and the storm remains over very warm
    sea-surface temperatures and high oceanic heat content. The
    hurricane-regional models have all responded by showing significant intensification after the vortex becomes vertically aligned,
    sometime in the 60-96 h period, though timing when this may occur is challenging. The intensity guidance is once again higher than the
    previous cycle, and the NHC intensity forecast was raised once
    again, showing Melissa becoming a hurricane in 72 h, rapidly
    intensifying into a major hurricane by 96 h, with additional
    intensification likely thereafter. This forecast is in the best
    agreement with the HCCA intensity aid, but it is worth noting it's
    under the latest HAFS-A/B and HMON forecasts. Unfortunately, it is
    becoming increasingly likely that Melissa will become a large and
    dangerous hurricane by the end of the forecast period.


    Key Messages:

    1. Melissa is forecast to meander over the central Caribbean Sea and
    could potentially become a major hurricane by early next week.
    Interests in Jamaica, Haiti, Cuba, and the Dominican Republic are
    urged to continue monitoring the latest forecasts.

    2. Due to Melissa's slow motion, the risk of a prolonged period of
    strong winds, possibly lasting for a day or more, is increasing for
    Jamaica and the Tiburon peninsula of Haiti. Preparations to protect
    life and property should be rushed to completion, since strong
    winds could begin in these areas as early as late Thursday or
    Friday and continue increasing over the weekend.

    3. Melissa is expected to produce heavy rainfall across portions of
    the Dominican Republic, Haiti, and Jamaica through this weekend,
    bringing a risk of significant, life-threatening flash flooding and
    numerous landslides.


    FORECAST POSITIONS AND MAX WINDS

    INIT 22/2100Z 14.4N 74.3W 45 KT 50 MPH
    12H 23/0600Z 14.6N 74.5W 45 KT 50 MPH
    24H 23/1800Z 14.9N 74.6W 50 KT 60 MPH
    36H 24/0600Z 15.2N 74.7W 50 KT 60 MPH
    48H 24/1800Z 15.6N 74.8W 55 KT 65 MPH
    60H 25/0600Z 16.1N 75.0W 60 KT 70 MPH
    72H 25/1800Z 16.3N 75.6W 70 KT 80 MPH
    96H 26/1800Z 16.2N 76.7W 100 KT 115 MPH
    120H 27/1800Z 16.0N 78.0W 115 KT 130 MPH

    $$
    Forecaster Papin



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