[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 200240
TCDAT5

Hurricane Nigel Discussion Number  19
NWS National Hurricane Center Miami FL       AL152023
1100 PM AST Tue Sep 19 2023

Nigel appears to be succumbing to the effects of southerly wind
shear this evening.  Deep convection in the eastern portion of the
circulation has eroded, and the eyewall has opened to the northeast.
Still, subjective and objective satellite intensity estimates range
between 102 to 77 kt.  The initial intensity is held at a possibly
generous 85 kt, to represent a blend of these estimates.

Global model guidance suggests oceanic and environmental conditions
could be marginally conducive for strengthening for only a short
while longer.  In a day or so, Nigel is expected to move over
waters cooler than 26 degrees Celsius, and the deep-layer vertical
wind shear is forecast to significantly increase.  As a result, the
latest NHC intensity forecast shows a slightly lower peak intensity
of 90 kt in the short-term forecast, followed by steady weakening
through the remainder of the forecast period.  Nigel should become
a powerful extratropical cyclone in about 60 h.

The hurricane is moving toward the north at 13 kt on the western
edge of a mid-level ridge over the central subtropical Atlantic.  By
Wednesday, Nigel is expected to turn northeastward and accelerate
in the flow of a deep-layer trough located over the northeastern
United States and Atlantic Canada.  In the first few days, there is
little spread in the track guidance envelope, and only minor
adjustments have been made to the latest official forecast.  As
Nigel moves poleward, the extratropical low is forecast to interact
with a broader cyclonic circulation over the north Atlantic on days
4 and 5, which introduces increased track uncertainty late in the
period.


FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 33.2N  54.7W   85 KT 100 MPH
 12H  20/1200Z 35.3N  54.2W   90 KT 105 MPH
 24H  21/0000Z 38.4N  51.3W   85 KT 100 MPH
 36H  21/1200Z 41.6N  46.1W   75 KT  85 MPH
 48H  22/0000Z 44.4N  39.0W   65 KT  75 MPH
 60H  22/1200Z 47.5N  31.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  23/0000Z 50.8N  25.9W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  24/0000Z 57.1N  22.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  25/0000Z 58.9N  21.5W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Bucci
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