[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 212032
TCDAT5

Tropical Storm Don Discussion Number  31
NWS National Hurricane Center Miami FL       AL052023
500 PM AST Fri Jul 21 2023

There has been a continued increase in banding in association
with Don today.  In visible satellite imagery, the primary
convective band wraps nearly completely around the center, however
the cloud tops have warmed over the northwestern portion of the
storm recently.  A late arriving ASCAT-C overpass that caught the
northwestern portion of Don this morning revealed peak winds in the
43-45 kt range.  Given the typical undersampling of that instrument
and the fact that it missed the potentially stronger northeastern
quadrant of the cyclone, the initial intensity has been increased
to 50 kt, which is a little above the latest subject Dvorak wind
speed estimates.

Despite the slightly stronger initial intensity, the overall
intensity forecast philosophy has not changed much.  Don will be
moving over the slightly warmer waters of the Gulf stream later
tonight and Saturday which could result in some slight
strengthening.  The official forecast allows for this possibility
and is close to the various intensity consensus aids through 24
hours.  By early Sunday, Don is forecast to move north of the Gulf
stream and over much colder SSTs, which should cause steady
weakening.  Simulated satellite imagery from the global models
suggest that Don will struggle to produce deep convection by late
Sunday, marking the system's transition to a post-tropical cyclone.
Dissipation is predicted just after 72 hours.

The storm has made its anticipated northwestward turn.  A mid-level
ridge to the north-northeast of Don is expected to shift eastward
during the next day or so and allow the cyclone to turn northward
on Saturday. After that time, Don is forecast to turn northeastward
within low- to mid-level southwesterly flow between the ridge and a
broad trough over eastern Canada.  The dynamical model envelope
made a noticeable eastward shift at 36 hours and beyond, which
required an eastward adjustment to the NHC track forecast.  The new
track lies along the western edge of the guidance envelope and is
not as fast east as the multi-model consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 36.6N  47.5W   50 KT  60 MPH
 12H  22/0600Z 37.9N  48.9W   55 KT  65 MPH
 24H  22/1800Z 40.0N  50.2W   55 KT  65 MPH
 36H  23/0600Z 42.4N  50.0W   50 KT  60 MPH
 48H  23/1800Z 44.6N  48.6W   40 KT  45 MPH...POST-TROPICAL
 60H  24/0600Z 47.1N  45.1W   35 KT  40 MPH...POST-TROPICAL
 72H  24/1800Z 48.7N  41.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  25/1800Z...DISSIPATED

$$
Forecaster Brown
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