[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 230236
TCDAT5

Hurricane Don Discussion Number  36
NWS National Hurricane Center Miami FL       AL052023
1100 PM AST Sat Jul 22 2023

Don's structure on satellite imagery remains well organized for a
tropical cyclone at such a high latitude in late July. A small but
distinct eye has persisted, surrounded by moderately cold cloud
tops. However, the coldest cloud tops are beginning to erode on the
north edge of the eye, and the upper-level outflow has also become
more restricted in that direction. These factors likely indicate
that Don is starting to feel the effects of nearby cooler waters
and increased vertical wind shear that will ultimately lead to a
swift decline in intensity. For now, the latest subjective Dvorak
estimates were T4.0 (65 kt) from both SAB and TAFB, and objective
intensity estimates currently range from 53 kt to 69 kt. It is
worth noting that UW-CIMSS ADT estimates have been much lower,
apparently due to that objective technique failing to pick up on the
eye pattern seen on satellite today. Discounting that outlier, a
blend of other subjective and objective data supports an initial
intensity of 65 kt for this advisory. Don's wind radii have also
been adjusted some due to a helpful ASCAT-B pass at 2348 UTC.

Now that Don is moving north of a warm eddy in the Gulf Stream, the
cyclone should soon encounter much colder sea-surface temperatures
along its track. Thus, steady weakening is expected to begin
shortly. As Don quickly loses its deep convection, the cyclone is
forecast to become post-tropical in 36 h, with the circulation
expected to open up into a trough axis after 48 h. This forecast is
in good agreement with the global and hurricane-regional model
guidance.

Don is now moving to the north-northeast a bit faster than before at
015/12 kt. A continued turn to the northeast with a bit more
acceleration is anticipated overnight into tomorrow as Don is
embedded within southwesterly steering flow between a subtropical
ridge to its southeast and a deep-layer trough located over eastern
Canada. This pattern should persist until Don dissipates, with the
system continuing to recurve eastward over the next 48 h. The track
guidance has shifted a bit faster than the prior cycle but still
remains along a similar trajectory. Thus the NHC track forecast
remains very close to the prior track, but just a little faster.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 41.4N  49.6W   65 KT  75 MPH
 12H  23/1200Z 43.3N  48.5W   55 KT  65 MPH
 24H  24/0000Z 45.5N  46.0W   45 KT  50 MPH
 36H  24/1200Z 47.2N  42.1W   35 KT  40 MPH...POST-TROPICAL
 48H  25/0000Z 48.1N  37.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
 60H  25/1200Z...DISSIPATED

$$
Forecaster Papin
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