Tropical Storm Nigel Forecast Discussion Number 8

By | September 17, 2023

Tropical Storm Nigel Discussion Number   8
NWS National Hurricane Center Miami FL       AL152023
500 AM AST Sun Sep 17 2023

Nigel's satellite structure has improved overnight as deep 
convection has taken on a distinct curved band appearance to the 
north of the estimated center. With that said, we have not 
received any recent microwave imagery to confirm if the low-level 
circulation has tightened up or has become more embedded in the deep 
convection, though derived motion winds from the 1-minute meso 
sector over the system do suggest the center has likely tucked 
underneath the convective cirrus canopy. Subjective Dvorak intensity 
estimates from TAFB and SAB were a consensus T3.0/45 kt, and the 
recent objective estimates from UW-CIMSS are in the 44-50 kt range. 
The initial intensity will be set at 45 kt, on the lower end given 
the uncertainty on the center position. 

Based on the estimated position, Nigel has been moving somewhat 
right of the prior track forecast, off to the north-northwest at 
330/12 kt. This continued rightward motion relative to the track 
forecast over the past 24 hours could be related to Margot eroding 
the mid-level ridging located northeast of Nigel, in addition to a 
mid- to upper-level trough favoring more convection on Nigel's 
eastern flank overall. However, as Margot continues to weaken, this 
mid-level ridging should rebuild, allowing Nigel to bend a bit more 
northwestward in the 24-48 hour time frame. By the middle of next 
week, the global model guidance is in good agreement that Nigel 
should recurve to the northeast as it gets picked up by a 
mid-latitude trough ejecting off the eastern U.S. coastline. The NHC 
track forecast continues to lie near the TVCA and HCCA consensus 
aids, which is a little east of the prior forecast, but not far off 
of a blend of the latest GFS and ECMWF models.

While it is unclear to know without recent microwave imagery if 
Nigel is in the early stages of developing an inner core, the 
improvement of the larger-scale structure on satellite suggests 
further intensification is likely. Both GFS- and ECMWF-based SHIPS 
guidance show vertical wind shear should remain low (under 10 kt) 
for the next 48-72 hours, while sea-surface temperatures remain 
between 28-30C. While mid-level relative humidity is a bit on the 
low side, this may only help to tighten up the core from its initial 
large origin assuming the shear remains low. SHIPS-RII and DTOPS 
continue to suggest a significant chance of rapid intensification 
over the next 2-3 days, and the latest NHC intensity forecast now 
shows Nigel peaking as a category 3 hurricane again. This is a bit 
higher than the IVCN and HCCA consensus aids, but close to the raw 
model output of the HAFS, HWRF, and COAMPS-TC models. By the end of 
the forecast, Nigel will likely be undergoing extratropical 
transition, though this process might not be complete until just 
beyond the 120 h point.


INIT  17/0900Z 23.0N  48.6W   45 KT  50 MPH
 12H  17/1800Z 24.5N  49.7W   55 KT  65 MPH
 24H  18/0600Z 26.0N  51.0W   65 KT  75 MPH
 36H  18/1800Z 27.5N  52.5W   80 KT  90 MPH
 48H  19/0600Z 28.8N  54.0W   95 KT 110 MPH
 60H  19/1800Z 30.5N  55.4W  100 KT 115 MPH
 72H  20/0600Z 32.7N  55.8W  100 KT 115 MPH
 96H  21/0600Z 38.0N  52.0W   85 KT 100 MPH
120H  22/0600Z 44.5N  40.0W   70 KT  80 MPH

Forecaster Papin


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