[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 200249
TCDAT5

Tropical Storm Don Discussion Number  24
NWS National Hurricane Center Miami FL       AL052023
300 AM GMT Thu Jul 20 2023

Don continues to maintain a compact area of deep convection, with
cold cloud tops between -60 to -65C attempting to rotate
cyclonically into the northern semicircle of the
storm's circulation. An earlier ASCAT-B pass clipped Don's east
side with a peak wind-retrieval of 39 kt, but this pass might
have missed higher winds closer to the center. In fact, a Synthetic
Aperture Radar (SAR) pass that became available after the prior
advisory suggests Don's radius of maximum wind has contracted to
near 20 n mi with a peak value of 49 kt, but this derived wind
may have been contaminated by ice-scattering noted in microwave
imagery. The most recent subjective Dvorak intensity estimate was
T3.0/45-kt from TAFB, and the most recent objective intensity
estimate from SATCON was 46 kt. A blend of these various data
sources supports increasing Don's intensity to 45 kt this advisory.

There is still a window for Don to intensify more over the next 24 h
while it remains over 25-26 C sea-surface temperatures (SSTs) and
low shear helps ongoing convection moisten up the nearby environment
in a compact area. Beyond that time, SSTs decrease markedly along
Don's track, related to the storm crossing its own cold wake. In
addition, both the GFS- and ECMWF-based SHIPS guidance show
environmental mid-level relative humidity dropping below 40 percent,
and Don's small core could become sensitive to any increase in
shear, which could introduce drier air from the northeast. The most
recent regional hurricane model simulations illustrate this possible
scenario, with convection becoming sheared off to the southwest as
dry air infiltrates the storm's core in 48-60 h. Thus, the NHC
intensity forecast continues to show a peak intensity of 50 kt, with
Don beginning to weaken after 48 h. This NHC forecast is near the
latest ICVN and HCCA consensus aids. The hurricane-regional guidance
also suggests Don should become devoid of convection when it moves
north of the Gulf Stream by 96 h, and the latest forecast now shows
the system becoming post-tropical at that time.

The tropical storm continues to move westward tonight, estimated at
270/5 kt. Don should soon begin to gain latitude again as a
prominent mid-level ridge becomes centered to its northeast. As
mentioned in the previous discussion, the model trends have been
for this blocking ridge to be slow to move completely out of Don's
way, and the storm is forecast to only slowly recurve into the
higher latitudes as a result. The track guidance this cycle has
shifted a bit westward compared to the previous forecast, notably
with the 18z ECMWF coming in farther west. The NHC track forecast
has also been shifted a little westward, but not as far west as the
TVCN and HCCA consensus aids, and further adjustments may be
necessary in subsequent advisories.


FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 33.9N  40.9W   45 KT  50 MPH
 12H  20/1200Z 34.0N  42.0W   50 KT  60 MPH
 24H  21/0000Z 34.5N  43.6W   50 KT  60 MPH
 36H  21/1200Z 35.3N  45.4W   50 KT  60 MPH
 48H  22/0000Z 36.6N  47.1W   50 KT  60 MPH
 60H  22/1200Z 38.3N  48.6W   45 KT  50 MPH
 72H  23/0000Z 40.2N  49.3W   45 KT  50 MPH
 96H  24/0000Z 43.9N  47.8W   40 KT  45 MPH...POST-TROPICAL
120H  25/0000Z 45.6N  42.5W   35 KT  40 MPH...POST-TROPICAL

$$
Forecaster Papin
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