Hurricane Gilma Forecast Discussion

331 
WTPZ42 KNHC 260240
TCDEP2

Hurricane Gilma Discussion Number  32
NWS National Hurricane Center Miami FL       EP072024
500 PM HST Sun Aug 25 2024

Gilma is a compact hurricane with a small eye noted in both
infrared satellite imagery and a recent 0039 UTC SSMIS microwave
overpass. The microwave imagery showed that the convection
associated with Gilma has eroded over the southern semicircle,
likely due to an increase in shear and dry air intrusion.  The
initial intensity has been lowered to 90 kt, which is a blend of
the latest objective and subjective intensity estimates.  It should
be noted that the range of the satellite intensity estimates is
atypically large and is around 75 kt on the low side to around 
100 kt at the upper end.

Westerly shear over Gilma is forecast to increase to moderate
levels during the next 24 hours, and this along with nearby dry
mid-level air and slightly lower SSTs are expected to cause gradual
weakening during the next couple of days.  Around 72 hours a more
substantial increase in vertical wind shear is anticipated and this
should result in a faster rate of weakening.  The global models
suggest the system is likely to struggle to produce organized
deep convection by day 4, and Gilma is forecast to become a
post-tropical cyclone around that time.

Gilma has been moving just north of due west (275/8 kt) during the
past 12 hours.  A mid-level ridge to the north of Gilma should
continue to steer the storm on a westward to west-northwestward
heading throughout much of this week.  The track guidance is in
good agreement during the next 48-72 hours, but there is greater
spread in Gilma's forward speed at days 4 and 5.  This is related 
to how long Gilma remains vertically coherent.  The models that 
weaken the cyclone more quickly favor a faster forward speed later 
in the forecast period. The NHC track forecast is a little faster 
at 96 and 120 h to be closer to the latest consensus aids. 
Otherwise, the new track forecast is essentially an update of
the previous official forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 18.1N 135.1W   90 KT 105 MPH
 12H  26/1200Z 18.2N 136.4W   85 KT 100 MPH
 24H  27/0000Z 18.4N 138.1W   75 KT  85 MPH
 36H  27/1200Z 18.6N 139.8W   70 KT  80 MPH
 48H  28/0000Z 18.9N 141.8W   65 KT  75 MPH
 60H  28/1200Z 19.2N 143.7W   55 KT  65 MPH
 72H  29/0000Z 19.6N 145.5W   50 KT  60 MPH
 96H  30/0000Z 20.3N 149.3W   35 KT  40 MPH...POST-TROPICAL
120H  31/0000Z 21.1N 153.6W   30 KT  35 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown