[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 180244
TCDAT5

Tropical Storm Don Discussion Number  16
NWS National Hurricane Center Miami FL       AL052023
300 AM GMT Tue Jul 18 2023

The convective structure of Don this evening has improved somewhat,
with a decent area of -55 to -65C cold cloud tops centered a bit to
the northeast of the low-level center. The center is also perhaps a
bit better defined than earlier, with the ongoing convective
activity possibly helping to tighten the center up. While subjective
Dvorak classifications have not increased much this evening, an
ASCAT-C pass at 2302 UTC caught the eastern portion of the
circulation, with several believable wind vectors of up to 35 kt.
Thus, Don is being upgraded to a tropical storm this advisory with
sustained winds of 35 kt.

Don continues to move southeastward at 125/11 kt. This motion is
expected to continue curving clockwise over the next several days as
the cyclone remains steered by a building mid-level ridge that is
forecast to shift southwestward to northwestward relative to Don.
Eventually this ridge will fold over the storm, allowing Don to
begin gaining latitude again in 48-60 h. Overall, the track guidance
this cycle has shifted a bit to the east and the NHC track has been
shifted a little in that direction, though still remains much
further west than the ECMWF model. There continues to be a large
spread in guidance solutions by the end of the forecast period, and
the current forecast remains low-confidence in that time frame.

Even though Don is a bit stronger currently, the overall forecast
environment is not all that conducive for much intensification in
the short-term. Sea-surface temperatures under the cyclone are
around 24C currently, and are only forecast to warm perhaps another
degree C over the next 36-48 h. However, model-derived soundings
from the GFS and HAFS models suggest that tropospheric instability
does increase as environmental temperatures subtly cool in the
mid-levels. The simulated IR imagery from these models around that
time shows better organization of convective activity around a
smaller core, and if this structure were to verify, some gradual
intensification is possible. The latest NHC intensity forecast shows
a bit more intensification than before, mostly related to the
initial intensity, but still caps the system off as a 45-kt tropical
storm by the end of the forecast period, which remains a bit under
the model consensus. The latter part of the forecast is likely
dependent on the Don's ultimate track. A further left track, like
the GFS and HAFS-A/B, may take the cyclone over warmer SSTs, and
result in a stronger storm. However, a more rightward track like
the ECMWF would take Don over its cold wake and likely would limit
additional intensification.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 37.4N  40.4W   35 KT  40 MPH
 12H  18/1200Z 36.3N  39.3W   35 KT  40 MPH
 24H  19/0000Z 34.9N  39.0W   35 KT  40 MPH
 36H  19/1200Z 34.1N  39.3W   35 KT  40 MPH
 48H  20/0000Z 33.8N  40.4W   40 KT  45 MPH
 60H  20/1200Z 34.2N  41.6W   40 KT  45 MPH
 72H  21/0000Z 35.0N  43.2W   45 KT  50 MPH
 96H  22/0000Z 37.4N  46.8W   45 KT  50 MPH
120H  23/0000Z 41.3N  49.2W   45 KT  50 MPH

$$
Forecaster Papin
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