[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 201443
TCDAT5

Hurricane Nigel Discussion Number  21
NWS National Hurricane Center Miami FL       AL152023
1100 AM AST Wed Sep 20 2023

Nigel is maintaining a ragged-appearing eye on visible and
infrared satellite imagery.  Bands of deep convection with tops to
around -70C continue to rotate around the center, and the system's
cloud pattern remains fairly symmetrical.  Although microwave
imagery from around 0900 UTC showed a closed eyewall, recent
geostationary images suggest breaks in the eyewall over the
eastern portion of the circulation.  Dvorak CI numbers from TAFB and
SAB are 4.5, corresponding to a 77-kt intensity, and an objective
ADT estimate from UW-CIMSS was 79 kt.  Based on these values, the
advisory intensity estimate was reduced only slightly, to 80 kt.
NOAA Hurricane Hunter aircraft are scheduled to investigate Nigel
soon.

The hurricane is moving northward, or perhaps slightly east of
north, with an initial motion of 010/16 kt.  The system has been
moving around the western periphery of a mid-level high pressure
area.  A mid-latitude trough to the northwest of Nigel should cause
the cyclone to turn toward the northeast and the cyclone
should continue to move northeastward at a faster forward speed over
the next couple of days.  In 48 to 72 hours, Nigel is expected to
rotate counter-clockwise around the eastern side of a large
extratropical cyclone over the north Atlantic.  Although the
official forecast shows track points at 4 and 5 days, there is a
good chance that Nigel will merge with,  or become absorbed by, the
other cyclone around that time.  The official forecast is very
similar to the previous NHC track prediction.

Nigel has only about 12 hours remaining before moving over cooler
waters, and southwesterly vertical shear is forecast to increase
tonight.  Gradual weakening is expected over the next 2-3 days, in
general agreement with the consensus intensity forecast guidance.
The intensity forecast in the latter part of the forecast period is
uncertain, given the distinct possibility that Nigel could merge
with the other extratropical cyclone.


FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 36.1N  54.4W   80 KT  90 MPH
 12H  21/0000Z 38.4N  51.8W   80 KT  90 MPH
 24H  21/1200Z 41.6N  46.4W   75 KT  85 MPH
 36H  22/0000Z 44.6N  39.0W   65 KT  75 MPH
 48H  22/1200Z 47.6N  31.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 60H  23/0000Z 51.3N  24.8W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  23/1200Z 55.0N  23.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  24/1200Z 57.0N  24.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  25/1200Z 58.0N  23.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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