[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 211436
TCDAT5

Hurricane Nigel Discussion Number  25
NWS National Hurricane Center Miami FL       AL152023
1100 AM AST Thu Sep 21 2023

Nigel is still maintaining some deep convection, with cloud tops
in bands to near -70 deg C.  However, increasing southwesterly
vertical wind shear is beginning to cause an elongation of the cloud
pattern toward the northeast.  Subjective Dvorak satellite
classifications from TAFB and SAB continue to give Current
Intensity numbers corresponding to 77 kt, and objective ADT
estimates from UW-CIMSS are a little lower than that value.  The
advisory intensity is held at 75 kt.

The current motion is quickly northeastward, or about 050/26 kt.
Nigel is embedded in the flow on the southeastern side of a strong
deep-layer mid-latitude trough.  This steering pattern should
continue to carry the cyclone rapidly toward the northeast through
tonight.  On Friday, Nigel should rotate around the eastern side of
a large extratropical cyclone over the North Atlantic.

Vertical wind shear over Nigel should become very high within the
next 24 hours, and the cyclone will be moving over significantly
cooler waters later today.  Therefore weakening should occur, and
global model guidance indicates that the system will become
embedded in a frontal zone by early Friday.  In 2 to 3 days, Nigel
is expected to merge with the large cyclone over the North
Atlantic, and dissipate.


FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 42.2N  45.0W   75 KT  85 MPH
 12H  22/0000Z 44.2N  38.8W   65 KT  75 MPH
 24H  22/1200Z 47.3N  30.8W   55 KT  65 MPH...POST-TROP/EXTRATROP
 36H  23/0000Z 51.0N  24.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  23/1200Z 55.2N  22.9W   50 KT  60 MPH...POST-TROP/EXTRATROP
 60H  24/0000Z 57.4N  24.4W   45 KT  50 MPH...POST-TROP/EXTRATROP
 72H  24/1200Z...DISSIPATED

$$
Forecaster Pasch
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