Hurricane Nigel Discussion Number  14
NWS National Hurricane Center Miami FL       AL152023
500 PM AST Mon Sep 18 2023

The center of Nigel is embedded within a central dense overcast of 
cold infrared cloud tops this afternoon. Recent GMI microwave images 
do not show much improvement to the hurricane's inner core 
structure, as it appears some drier air could be intruding into the 
north side of the circulation. There is no eye feature apparent in 
conventional satellite imagery at this time. The latest subjective 
Dvorak estimates are T4.0 (SAB) and T4.5 (TAFB). Meanwhile, the 
latest UW-CIMSS ADT and SATCON intensity estimates are 63 kt and 71 
kt, respectively. A blend of these data support holding the initial 
intensity at 70 kt for this advisory.

Despite seemingly conducive environmental conditions for 
strengthening, Nigel's intensification appears to have been 
disrupted, possibly by dry air entrainment related to some mid-level 
shear. If the hurricane can solidify its inner core during the next 
day or so, the very warm SSTs and relatively low shear should allow 
for some strengthening in the near term. The NHC forecast has been 
slightly lowered from the previous one but still shows Nigel peaking 
near major hurricane intensity in 36-48 h. This prediction lies 
above the latest intensity guidance, closest to HCCA and some of the 
regional hurricane models (HAFS-A). Beyond 48 h, increasing 
deep-layer shear associated with the upper trough and rapidly 
cooling SSTs are forecast to induce steady weakening through the 
rest of the period.

A mid-level ridge over the central Atlantic continues to steer Nigel 
northwestward (320/10 kt). The hurricane is expected to turn 
northward over the next couple of days while it moves around the 
western periphery of this steering ridge. Then, an upper-level 
trough moving across the western Atlantic is forecast to cause Nigel 
to accelerate northeastward and move deeper in the mid-latitudes 
through late this week. The NHC forecast remains near the center of 
the tightly clustered track guidance, with a faster forward motion 
shown later in the period in agreement with the TVCA and HCCA aids. 
This takes Nigel more quickly into the mid-latitudes, and the latest 
global model fields and phase diagrams suggest its extratropical 
transition should be complete by 96 h.


FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 28.0N  52.2W   70 KT  80 MPH
12H  19/0600Z 29.2N  53.3W   80 KT  90 MPH
24H  19/1800Z 31.0N  54.5W   90 KT 105 MPH
36H  20/0600Z 33.4N  54.8W   95 KT 110 MPH
48H  20/1800Z 36.2N  53.5W   95 KT 110 MPH
60H  21/0600Z 39.1N  50.0W   85 KT 100 MPH
72H  21/1800Z 42.1N  43.9W   75 KT  85 MPH
96H  22/1800Z 48.0N  29.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  23/1800Z 56.0N  18.0W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster B Reinhart/A Reinhart