[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 180239
TCDAT5

Tropical Storm Nigel Discussion Number  11
NWS National Hurricane Center Miami FL       AL152023
1100 PM AST Sun Sep 17 2023

Proxy-vis and infrared satellite imagery show that Nigel is
becoming better organized and continues to strengthen this evening.
Deep convection continues to burst near the center, with cold cloud
tops to -80 degrees Celsius. An earlier SSMI/S microwave pass
depicts that an inner core has developed and it is vertically
aligned with the low-level center. Subjective Dvorak estimates from
TAFB and SAB were T4.0/T3.5, respectively. Given a blend of these
estimates, the initial intensity is increased to 60 kt for this
advisory.

Nigel is moving north-northwestward with an estimated motion of
330/10 kt. This general north-northwestward heading should continue
for the next couple of days as a mid-level ridge builds to the
northeast of the system. In about 2 to 3 days, Nigel should begin
to round the western edge of the ridge and move more northward. By
the end of the forecast period, a strong trough will pick up the
system, and Nigel should accelerate towards the northeast. The NHC
track forecast is similar to the previous advisory, and lies near
the simple and corrected consensus aids.

The environment around Nigel is conducive for steady to rapid
intensification. Vertical wind shear is fairly low, with warm sea
surface temperatures, and outflow aloft continues to become more
pronounced.  The SHIPS and DTOPS rapid intensification (RI) indices
continue to show above climatological normal chances of RI. Given
the improving structure and the favorable environment, the NHC
intensity forecast reflects this and forecasts rapid
intensification over the next 24-36 hrs, with Nigel expected to
become a hurricane overnight, and a major hurricane on Tuesday.
Towards the end of the period, Nigel will likely become a strong
extratropical cyclone as the aforementioned trough picks up the
system, and it becomes embedded within a frontal zone. The NHC
intensity forecast lies near the upper-end of the guidance envelope,
closest to the HCCA and IVCN intensity consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 25.8N  50.2W   60 KT  70 MPH
 12H  18/1200Z 27.0N  51.3W   75 KT  85 MPH
 24H  19/0000Z 28.5N  52.8W   90 KT 105 MPH
 36H  19/1200Z 30.1N  54.2W  100 KT 115 MPH
 48H  20/0000Z 32.1N  55.2W  100 KT 115 MPH
 60H  20/1200Z 34.4N  54.8W   95 KT 110 MPH
 72H  21/0000Z 37.4N  52.5W   90 KT 105 MPH
 96H  22/0000Z 43.1N  42.1W   75 KT  85 MPH
120H  23/0000Z 50.8N  28.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Kelly
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