[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 201445
TCDAT3

Tropical Storm Bret Discussion Number   5
NWS National Hurricane Center Miami FL       AL032023
1100 AM AST Tue Jun 20 2023

Bret's low-level center has become exposed this morning, surrounded
by bands of deep convection in nearly all quadrants.  Upper-level
outflow still appears established over the system, but the exposed
center may suggest that some moderate westerly shear is affecting
Bret below the cirrus level.  Bret's initial intensity remains 35
kt based on T2.5 Dvorak classifications from TAFB and SAB.
Scatterometer passes continue to miss Bret, keeping us from getting
a better handle on the system's intensity and size.

Global model forecast fields suggest that the mid-level westerly
shear affecting Bret is unlikely to abate during the next few days,
and it's likely that deeper-layer shear will also increase in about
2 to 3 days.  This forecast scenario has led to some changes in
Bret's intensity forecast.  Aside from the HWRF, which is an
outlier scenario, none of the other reliable intensity models bring
Bret to hurricane intensity.  In addition, all of the global models
show Bret opening up into a trough in 2 to 4 days as it's passing
the Lesser Antilles or after it moves into the eastern Caribbean
Sea.  As a result, Bret's forecast intensity in the NHC prediction
has been decreased, still allowing for the possibility of some
strengthening, but keeping the system below hurricane strength.  In
addition, the new forecast now shows dissipation by day 5, but if
the global models are correct, that could occur even sooner.

Bret is moving a little faster toward the west, or 275/18 kt.
Low- to mid-level ridging over the Atlantic is expected to keep
Bret on a westward trajectory through the forecast period, with
only some slight fluctuations in forward speed.  The track guidance
has shifted southward on this cycle, under the assumption that
low-level ridging will have a greater impact on preventing a
weaker Bret from gaining much latitude.  One important note is that
the weaker Bret remains, it could also move faster than what is
shown in the NHC forecast (and what is suggested by the ECWMF
model).


KEY MESSAGES:

1. Bret is forecast to approach the Lesser Antilles through
early Thursday and then move across the islands Thursday and
Thursday night as a tropical storm, bringing a risk of flooding
from heavy rainfall, strong winds, and dangerous waves along the
coast.

2. Given the larger-than-usual uncertainty in the track and
intensity forecasts, it is too early to specify the location and
magnitude of where Bret's associated hazards could occur.  However,
everyone in the Lesser Antilles, Puerto Rico, and the Virgin Islands
should closely monitor updates to the forecast for Bret.  Tropical
storm watches may be required for portions of the Lesser Antilles
later today or tonight.


FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 11.9N  47.0W   35 KT  40 MPH
 12H  21/0000Z 12.3N  49.2W   40 KT  45 MPH
 24H  21/1200Z 12.7N  51.9W   45 KT  50 MPH
 36H  22/0000Z 13.2N  54.5W   50 KT  60 MPH
 48H  22/1200Z 13.6N  57.3W   55 KT  65 MPH
 60H  23/0000Z 13.9N  60.4W   55 KT  65 MPH
 72H  23/1200Z 14.2N  63.6W   50 KT  60 MPH
 96H  24/1200Z 14.4N  70.4W   45 KT  50 MPH
120H  25/1200Z...DISSIPATED

$$
Forecaster Berg
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