[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 202047
TCDAT3

Tropical Storm Bret Discussion Number   6
NWS National Hurricane Center Miami FL       AL032023
500 PM AST Tue Jun 20 2023

A burst of deep convection developed over Bret's center during the
past several hours, although a 1641 UTC AMSR2 microwave pass showed
that most of the convective activity is located within a band
wrapping around the east side of the circulation.  Based on the
slightly improved convective structure, the initial intensity is
raised to 40 kt, which is a blend of T2.5/35 kt and T3.0/45 kt
Dvorak estimates from TAFB and SAB, respectively.

Despite upper-level cirrus clouds radiating away from the storm in
all quadrants, it still appears that there is some westerly shear
affecting the system below the cirrus level.  Global model
forecasts suggest that this setup will continue for the next couple
of days, but it shouldn't be strong enough to prevent some
additional strengthening while Bret approaches the Lesser Antilles.
The NHC intensity forecast is very close to the HCCA and IVCN
consensus aids through 60 hours, and continues to show Bret
crossing the islands as a 55-kt tropical storm.  Just after
that time, Bret will be approaching an upper-level trough located
over the eastern Caribbean Sea, and that feature is likely to cause
more significant deep-layer shear over the storm by Friday.
Because of the increase in shear, all of the global models show
Bret opening up into a trough by day 4.  For continuity purposes,
the official forecast continues to show a day 4 point, but it's
likely that Bret will have dissipated by then.

The initial motion remains westward, or 280/17 kt.  There is very
little change to the forecast track reasoning, with low- to
mid-level ridging expected to steer Bret toward the west until it
dissipates by day 4.  The track guidance has not shifted any
farther south on this cycle, so the new NHC track forecast is very
similar to the previous one.  Users are reminded that NHC's track
forecasts have average errors of 60 to 75 n mi from 48 to 60 hours,
and it is too soon to know exactly where Bret's center will move
across the Lesser Antilles chain.


KEY MESSAGES:

1. Bret is forecast to approach the Lesser Antilles through
Thursday morning and then move across the islands Thursday
afternoon 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 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.  A Tropical Storm Watch has been
issued for Barbados, and additional watches are likely for other
islands within the Lesser Antilles later tonight.


FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 12.2N  48.6W   40 KT  45 MPH
 12H  21/0600Z 12.6N  50.8W   45 KT  50 MPH
 24H  21/1800Z 13.1N  53.4W   50 KT  60 MPH
 36H  22/0600Z 13.5N  55.9W   55 KT  65 MPH
 48H  22/1800Z 13.9N  58.8W   55 KT  65 MPH
 60H  23/0600Z 14.2N  62.0W   55 KT  65 MPH
 72H  23/1800Z 14.4N  65.6W   50 KT  60 MPH
 96H  24/1800Z 14.7N  73.0W   40 KT  45 MPH
120H  25/1800Z...DISSIPATED

$$
Forecaster Berg
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