[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 060848
TCDAT5

Tropical Storm Elsa Discussion Number  24
NWS National Hurricane Center Miami FL       AL052021
500 AM EDT Tue Jul 06 2021

Elsa is now located over the Florida Straits, with
tropical-storm-force wind gusts occurring across the Lower and
Middle Keys.  Doppler radar data and satellite images indicate that
the core of Elsa is fairly small and has maximum winds of around 50
kt. The outer rainbands associated with Elsa are spreading northward
across southern Florida, and a cluster of deep convection has been
lingering over portions of central and western Cuba.  The Air Force
Hurricane Hunters will be investigating Elsa later this morning, and
the data the plane collects will be valuable in assessing the
storm's intensity and structure.

Elsa is moving to the north-northwest at about 10 kt on the western
periphery of a subtropical ridge that is located over the central
Atlantic.  The storm should turn northward later today as it moves
in the flow between the ridge and a mid- to upper-level low over the
south-central U.S.  This motion should take the core of Elsa
parallel to and likely just offshore of the west coast of Florida
through tonight.  After that time, a slight turn to the
north-northeast is forecast as another trough moves across the
north-central U.S.  This slight change in heading should bring Elsa
inland across the Big Bend region of Florida by early Wednesday and
then across coastal Georgia and the Carolinas Wednesday night
through early Friday.  Thereafter, the storm is expected to
accelerate and move northeastward off the mid-Atlantic and New
England coasts.  The NHC track forecast is basically unchanged from
the previous one and lies close to the model consensus aid TVCA.

Now that Elsa is gradually pulling away from Cuba, it will have an
opportunity to strengthen.  However, the environmental conditions
are only marginal for the storm to do so.  Dry air on the western
side of the cyclone and some westerly shear should prevent rapid
intensification, but the small cyclone will likely strengthen slowly
before it moves inland over the Big Bend of Florida.  The GFS model
shows Elsa deepening by 5-10 mb before landfall, and the ECMWF shows
even greater pressure falls.  Based on these models, the intensity
forecast is nudged upward and now shows Elsa just below hurricane
force before landfall in Florida. After Elsa moves inland, steady
weakening is forecast, but the system is expected to restrengthen
over the western Atlantic as it transitions into an extratropical
cyclone.

Based on this new forecast, a Hurricane Watch has been issued for a
portion of the west-central and Big Bend Florida coast. In addition,
it should be noted that much of the west coast of the Florida
Peninsula is expected to see wind, rain, and surge impacts since
that region will be on Elsa's east side.  A Tropical Storm Watch
has also been issued for the Georgia coast and portions of the
South Carolina coast.


Key Messages:

1. Heavy rain will impact Cuba today resulting in significant
flooding and mudslides. As Elsa moves across the western Florida
Peninsula through Wednesday, heavy rainfall may result in isolated
flash, urban, and minor river flooding, with considerable flash and
urban flooding possible in southwest and western portions of
Florida.  Mid to late week, heavy rainfall across coastal Georgia,
South Carolina, North Carolina, and southeastern Virginia may result
in isolated flash and urban flooding, with considerable flash and
urban flooding possible across coastal Georgia and the Lowcountry of
South Carolina.

2. There is a danger of life-threatening storm surge along portions
of the west coast of Florida tonight and Wednesday, and a Storm
Surge Warning is in effect for that area.

3. A Hurricane Watch has been issued for a portion of the
west-central and Big Bend coast of Florida, where hurricane
conditions are possible tonight and early Wednesday.  Tropical
storm conditions are expected across portions of the Florida Keys
and much of the west coast of the state, where a Tropical Storm
Warning is in effect.

4. A Tropical Storm Watch has been issued for the Georgia coast and
portions of the South Carolina coast, where tropical storm
conditions are possible late Wednesday and early Thursday.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 24.1N  82.4W   50 KT  60 MPH
 12H  06/1800Z 25.7N  82.9W   55 KT  65 MPH
 24H  07/0600Z 28.0N  83.1W   60 KT  70 MPH
 36H  07/1800Z 30.4N  82.5W   40 KT  45 MPH...INLAND
 48H  08/0600Z 32.9N  81.0W   30 KT  35 MPH...INLAND
 60H  08/1800Z 35.5N  78.2W   30 KT  35 MPH...INLAND
 72H  09/0600Z 38.5N  74.3W   35 KT  40 MPH...OVER WATER
 96H  10/0600Z 45.9N  62.8W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  11/0600Z 54.7N  48.4W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi/Reinhart
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