[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 180844
TCDAT5

Hurricane Nigel Discussion Number  12
NWS National Hurricane Center Miami FL       AL152023
500 AM AST Mon Sep 18 2023

Infrared satellite imagery indicates that Nigel is getting better
organized in a hurry.  Deep convective towers have been quickly
rotating around a developing eyewall, and an AMSR2 microwave pass
indicated that a low-level eye feature had developed.  Intensity
estimates at 06 UTC ranged from 60-70 kt, and given the increasing
organization on satellite and microwave data, the initial wind speed
is raised to 70 kt.

It seems like the long-awaited rapid intensification phase of Nigel
is underway.  Very deep convective cloud tops are in the central
dense overcast, with warm waters and light shear for at least a day
or two along the path of the hurricane.  These conditions should
promote significant strengthening, and it makes sense to forecast a
period of rapid intensification, only moderated by somewhat cooler
waters after 36 hours, along with possible eyewall replacement
cycles.  It is interesting to note that most of the regional
hurricane guidance has come down this cycle, with the hurricane
models showing a very deep, but larger system with lower maximum
winds.  The new forecast is closer to the previous NHC interpolated
forecast, the statistical aids, and the COAMPS-TC ensemble.  Nigel
should undergo a quick extratropical transition between days 4 and
5, consistent with all of the global model predictions.

Nigel is moving northwestward with an estimated motion of 325/10 kt.
This general northwestward to north-northwestward heading should
continue for the next couple of days as a mid-level ridge builds to
the northeast of the system. In a couple of days, Nigel will reach
the western edge of the ridge and turn more northward. By the end of
the forecast period, a strong trough will pick up the system, and
Nigel should accelerate quite rapidly towards the northeast. There
are no significant changes to report with the latest NHC track
forecast, as at last the rightward shift of the guidance seems to
have ended.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 26.5N  50.7W   70 KT  80 MPH
 12H  18/1800Z 27.6N  51.8W   85 KT 100 MPH
 24H  19/0600Z 29.1N  53.3W  100 KT 115 MPH
 36H  19/1800Z 30.8N  54.6W  105 KT 120 MPH
 48H  20/0600Z 33.1N  55.0W  100 KT 115 MPH
 60H  20/1800Z 35.7N  53.9W   95 KT 110 MPH
 72H  21/0600Z 38.5N  50.8W   90 KT 105 MPH
 96H  22/0600Z 44.5N  37.3W   70 KT  80 MPH
120H  23/0600Z 51.5N  21.5W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake
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