[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 020852
TCDAT5

Tropical Storm Elsa Discussion Number   7
NWS National Hurricane Center Miami FL       AL052021
500 AM AST Fri Jul 02 2021

Elsa appears to be slowly gaining strength as it nears the Lesser
Antilles.  Deep convection has been increasing, and accordingly, the
latest Dvorak estimates have nudged upward.  The initial intensity
is increased to 50 kt, but some of the estimates are a little
higher.  Radar data from Barbados indicate that a small inner core
could be forming, and it seems likely that the center will pass very
near or over the island later this morning.  An Air Force Hurricane
Hunter aircraft is scheduled to be in the storm in a few hours, and
the data collected by the plane should provide a better estimate of
Elsa's intensity and structure.

The tropical storm is moving quickly to the west-northwest at about
24 kt.  A subtropical ridge should continue to steer Elsa briskly to
the west-northwest during the next day or two, taking the storm
across the eastern and central Caribbean Sea.  After that time, a
decrease in forward speed and a gradual turn to the north is
expected toward a weakness in the ridge. There has not been much
change in the latest model runs with the GFS and UKMET models on the
left side of the guidance and the ECMWF still on the right side.
The spread in the ensemble members of the GFS and ECMWF is very
large and range from tracks across or east of the Bahamas to the
Yucatan Peninsula.  The NHC track forecast continues to hold steady
and lies roughly near the middle of the guidance envelope. As
stated in previous discussions, this is a low confidence track
forecast given the large spread in the models.

In the short term, while Elsa moves across the warm Caribbean
waters, some additional strengthening seems likely.  However, the
fast forward speed of the storm and associated mid-level wind shear
should prevent significant intensification. Since the new forecast
is a little higher than the previous one and shows peak winds just
below hurricane force on Saturday near Haiti, tropical storm
warnings have been issued for portions of the Dominican Republic and
Haiti and a hurricane watch is now in effect for the southern
portion of Haiti out of abundance of caution.  The degree of land
interaction with the mountainous islands of Hispaniola and Cuba will
be a big factor in the future strength of Elsa at days 4 and 5.
Like the track forecast, there is a huge model spread with solutions
ranging from dissipation in the Caribbean to a category 3 hurricane.
Given the uncertainty, the intensity forecast generally keeps the
storm steady in strength from 24 to 120 h, and it remains on the low
side of the model guidance.

It should be noted that the average NHC track errors are 175 miles
and 200 miles at days 4 and 5, respectively.  Given the larger-than-
normal uncertainty and because hazards will extend well away from
the center of the storm, users are urged to not focus on the exact
forecast points.

Key Messages:

1. Tropical storm conditions are expected to begin later this
morning in portions of the Windward and Leeward Islands. Tropical
storm conditions are expected and hurricane conditions are possible
over southern portions of Hispaniola on Saturday. Tropical storm
conditions are possible over Jamaica beginning Saturday night.

2. Heavy rainfall from Elsa will move quickly across the Windward
and southern Leeward Islands today, including Barbados. Outer rain
bands will impact Puerto Rico late today into Saturday, and southern
Hispaniola and Jamaica Saturday into Sunday. Flooding and mudslides
are possible.

3. There is a risk of wind and rainfall impacts in portions of
Cuba, the Turks and Caicos, and the Bahamas through early next
week. Interests in these areas should monitor Elsa's progress and
updates to the forecast.

4. There is a risk of storm surge, wind, and rainfall impacts in the
Florida Keys and portions of the Florida Peninsula early next week.
However, the forecast uncertainty remains larger than usual due to
Elsa's potential interaction with the Greater Antilles this weekend.
Interests in Florida should monitor Elsa's progress and updates to
the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0900Z 12.7N  58.6W   50 KT  60 MPH
 12H  02/1800Z 13.8N  62.4W   55 KT  65 MPH
 24H  03/0600Z 15.4N  67.4W   60 KT  70 MPH
 36H  03/1800Z 17.1N  71.7W   60 KT  70 MPH
 48H  04/0600Z 18.7N  75.2W   60 KT  70 MPH
 60H  04/1800Z 20.2N  77.8W   55 KT  65 MPH
 72H  05/0600Z 21.7N  79.7W   55 KT  65 MPH
 96H  06/0600Z 25.2N  82.2W   55 KT  65 MPH
120H  07/0600Z 29.2N  82.6W   55 KT  65 MPH

$$
Forecaster Cangialosi/Berg
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