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