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