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Hurricane Fernanda Discussion Number   6
NWS National Hurricane Center Miami FL       EP072023
500 PM HST Sun Aug 13 2023
 
Fernanda continues to rapidly intensify this evening. Since the 
prior advisory, the eye signature on visible satellite has become 
much more distinct as infrared cold cloud tops between -65 to -75 C 
have grown and encircled the eye. The last few microwave passes 
indicate quickly improving structure, with a 2331 UTC GMI pass 
showing a thick closed eyewall on the 89 and 37 GHz channels. 
Satellite intensity estimates have responded by rapidly increasing, 
with subjective estimates at 0000 UTC from TAFB and SAB between 77- 
to 90-kt, and objective estimates covering a similar range. Given 
the improvement of Fernanda's structure on satellite since that 
time, the initial intensity is set near the top of those estimates 
at 90 kt this advisory.
 
The hurricane continues to move generally westward to 
west-northwestward at 280/8 kt. As mentioned previously, the 
hurricane has been moving rather slowly over the last 24 hours due 
to a weak mid-level ridge that has been eroded some by a cutoff low 
located further north near the California coast. However, the 
ridging north of Fernanda should gradually build back in as this 
cutoff low retrogrades off to the northwest. The net effect of this 
change should lead to the hurricane gradually accelerating over the 
next several days. As Fernanda becomes more vertically shallow 
towards the end of the forecast, it should also turn more westward. 
The official track forecast is quite similar to the prior one, but 
just a little faster, favoring a blend of the latest HCCA and TVCE 
consensus aids.
 
Given the most recent microwave imagery showing Fernanda developing 
a well-defined single closed eyewall, the hurricane seems poised to 
continue rapidly intensifying. Vertical wind shear is forecast to 
remain under 5 kt and sea-surface temperatures (SSTs) remaining near 
29 C for the next day or so. In fact, SHIPS-RII shows a 67 percent 
chance of another 30 kt increase in intensity over the next 24 
hours, and the latest NHC intensity forecast now shows Fernanda 
becoming a powerful Category 4 hurricane in the next day or so. 
Thereafter, Fernanda will move into an increasingly dry and stable 
environment, as SSTs rapidly drop off along the forecast track. 
These negative factors should lead to initially gradual, and 
then more rapid weakening towards the second half of the forecast 
period. The latest NHC intensity forecast is above most of the 
guidance over the next 24 hours, in light of its continued rapid 
intensification, but falls back closer to the HCCA and IVCN 
intensity aids between days 2-4. Both the GFS and ECMWF models 
suggest the cyclone will become devoid of organized convection by 
120 hours, and the latest intensity forecast now shows the system 
becoming a remnant low by that time.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  14/0300Z 15.6N 117.2W   90 KT 105 MPH
 12H  14/1200Z 15.8N 118.3W  105 KT 120 MPH
 24H  15/0000Z 16.3N 119.8W  115 KT 130 MPH
 36H  15/1200Z 16.9N 121.6W  105 KT 120 MPH
 48H  16/0000Z 17.2N 123.8W   95 KT 110 MPH
 60H  16/1200Z 17.3N 126.3W   75 KT  85 MPH
 72H  17/0000Z 17.4N 129.0W   65 KT  75 MPH
 96H  18/0000Z 17.7N 134.6W   40 KT  45 MPH
120H  19/0000Z 18.0N 140.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Papin
 
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