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Hurricane Gilma Discussion Number  19
NWS National Hurricane Center Miami FL       EP072024
500 PM HST Thu Aug 22 2024
 
Gilma's satellite presentation has degraded this evening, with the 
eye becoming cloud filled and more irregularly shaped.  Dvorak 
Current Intensity estimates remain unchanged from TAFB (6.0/115 kt) 
and SAB (5.5/102 kt) from earlier today, but most objective numbers 
from UW-CIMSS now range between 95 and 105 kt.  105 kt is set as the 
initial intensity as a blend of these numbers and the general 
degradation of the eye definition.

Gilma's forward speed is now down to 5 kt toward the west-northwest. 
A deep-layer trough over the U.S. West Coast is expected to 
gradually move eastward, allowing mid-level high pressure to build 
offshore.  This should cause Gilma to very gradually accelerate 
toward the west-northwest and then west through the entire 5-day 
forecast period.  There is high confidence in Gilma's forecast 
track given a tightly packed guidance suite, and the updated NHC 
track prediction has only been pushed northward a shade, following 
the latest consensus trends.  On the current forecast track, Gilma 
would move into the central Pacific basin late Monday.
 
The ocean heat content near Gilma is only about 8 units (for 
reference, ocean heat content in the northwestern Caribbean Sea and 
Gulf of Mexico exceeds 100 units).  Therefore, it is likely that 
the hurricane's very slow motion is upwelling cold water from 
below, which may be contributing to the recent degradation in the 
satellite appearance.  Cold water upwelling will probably continue 
for the next couple of days while Gilma's forward speed remains 8 
kt or less, and despite a relatively low-shear environment, 
gradual weakening is forecast to continue through the entire 
forecast period.  The new NHC forecast has been adjusted downward, 
but it still lies near the northern bound of the guidance suite.  
Global model guidance suggests that the cool waters, a drier 
environment, and increased shear may cause Gilma to struggle to 
maintain deep convection by early next week, and the new forecast 
now shows the cyclone becoming post tropical by day 5.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0300Z 17.3N 125.5W  105 KT 120 MPH
 12H  23/1200Z 17.6N 126.6W  100 KT 115 MPH
 24H  24/0000Z 18.0N 128.1W   95 KT 110 MPH
 36H  24/1200Z 18.4N 129.8W   90 KT 105 MPH
 48H  25/0000Z 18.8N 131.5W   85 KT 100 MPH
 60H  25/1200Z 19.0N 133.3W   80 KT  90 MPH
 72H  26/0000Z 19.2N 135.3W   70 KT  80 MPH
 96H  27/0000Z 19.8N 139.8W   55 KT  65 MPH
120H  28/0000Z 20.5N 145.3W   35 KT  40 MPH...POST-TROPICAL
 
$$
Forecaster Berg
 
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