Hurricane Gilma Forecast Discussion

000
WTPZ42 KNHC 222035
TCDEP2

Hurricane Gilma Discussion Number  18
NWS National Hurricane Center Miami FL       EP072024
1100 AM HST Thu Aug 22 2024

Gilma has maintained an impressive satellite appearance, with a
clear warm eye surrounded by a ring of -60 to -70 C cold cloud
tops. An SSMIS microwave pass received after the prior advisory
showed the eyewall remains well organized and mostly closed, with
only a limited number of rainbands observed outside of the inner
core. Subjective Dvorak satellite estimates were CI 5.5/102 kt from 
SAB and 6.0/115 kt from TAFB, while objective intensity estimates 
largely fell in between these values. Thus, the initial intensity 
is being held at 110 kt for this advisory. A helpful scatterometer 
pass was used to help adjust some of the 34-kt and 50-kt radii this 
advisory. 

The hurricane continues to move slowly west-northwestward across the 
central portion of the East Pacific basin, with its estimated motion 
at 290/6 kt. This general motion is expected to continue over the 
next several days as Gilma is primarily influenced by a narrow 
mid-level ridge to its north, though a gradual turn more westward 
with some increase in forward motion is anticipated by early next 
week as mid-level ridging builds in a bit more towards the end of 
the forecast period. The track guidance this cycle is a bit more 
poleward and a little faster than the prior cycle, and the NHC track 
forecast was nudged in that direction, blending the previous 
forecast track with the track consensus aids. 

While I can not rule out a bit of additional intensification in the 
short-term, the slow motion of Gilma could also make it susceptible 
to upwelling cooler ocean waters underneath it. However, at the same 
time, vertical wind shear as diagnosed by the GFS-SHIPS is expected 
to remain quite low, under 10 kt for at least the next 48-60 h. Some 
of the regional-hurricane models also suggest that Gilma may take 
on some annular characteristics, with limited outer bands as the 
eyewall remains intact, and current satellite imagery suggests that 
appearance may already be taking shape. Since these storms are known 
to weaken slower than expected by the cooler sea-surface 
temperatures underneath, the NHC intensity forecast only shows very 
gradual weakening over the next couple of days, which is higher than 
the majority of the intensity guidance, aside from the HAFS-A/B 
runs. Thereafter, westerly shear is forecast to increase as SSTs 
remain in the 25-26 C range, and a faster rate of weakening is 
anticipated by the end of the forecast period, more in line with the 
intensity consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 17.0N 125.0W  110 KT 125 MPH
 12H  23/0600Z 17.4N 126.0W  110 KT 125 MPH
 24H  23/1800Z 17.7N 127.4W  105 KT 120 MPH
 36H  24/0600Z 18.1N 129.0W  100 KT 115 MPH
 48H  24/1800Z 18.5N 130.6W   95 KT 110 MPH
 60H  25/0600Z 18.7N 132.4W   90 KT 105 MPH
 72H  25/1800Z 18.9N 134.4W   80 KT  90 MPH
 96H  26/1800Z 19.5N 138.5W   60 KT  70 MPH
120H  27/1800Z 20.0N 143.5W   45 KT  50 MPH

$$
Forecaster Papin