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