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Hurricane Fernanda Discussion Number  11
NWS National Hurricane Center Miami FL       EP072023
1100 PM HST Mon Aug 14 2023

Fernanda continues to show signs of weakening this evening, with the 
once-visible and distinct eye from earlier today having vanished 
and now cloud filled. Microwave passes from this evening depict that 
the inner core of Fernanda has started to lose its well-defined 
structure. This is reflected in the recent infrared satellite trends 
showing the ring of cold cloud tops becoming less organized, and 
not as tightly wrapped around the center. Subjective final-T Dvorak 
numbers from TAFB and SAB for this advisory were T5.5/T4.5, 
respectively. CIMMS ADT and AiDT estimates have started 
to drop as well, and lie between the TAFB and SAB estimates. Given 
the decline in satellite appearance, and using a blend of the 
satellite estimates, the initial intensity for this advisory is 
lowered to 95 kt.
 
The hurricane is being steered by a weak mid-level ridge with a 
generally west-northwest to westward motion expected throughout the 
period. The hurricane will begin to gradually increase in forward 
speed over the next several days, as the aforementioned mid-level 
ridge strengthens and builds westward. The official track forecast 
is similar to the previous forecast, and the track remains close to 
both the simple and corrected consensus model guidance.
 
Fernanda is moving into a less favorable environment, which is 
expected to cause fairly quick weakening. Southerly mid-level 
vertical wind shear is starting to increase over the cyclone, and 
will increase to 15 to 20 kt. The system is also moving into a 
fairly stable, and much drier airmass, with mid-level relative 
humidity values plummeting to below 40 percent in about 24 hours. 
In addition, sea surface temperatures also begin to rapidly cool 
in 24 to 36 hours. Given these conditions, simulated satellite 
imagery from both the GFS and ECMWF show the system void of most of 
its convection in about 60h.  This is now reflected in the latest 
NHC intensity forecast, which shows a little faster weakening 
trend, and the system now becoming post-tropical at 60 hours.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/0900Z 16.9N 120.7W   95 KT 110 MPH
 12H  15/1800Z 17.3N 122.3W   85 KT 100 MPH
 24H  16/0600Z 17.7N 124.7W   65 KT  75 MPH
 36H  16/1800Z 17.9N 127.3W   50 KT  60 MPH
 48H  17/0600Z 18.0N 130.0W   40 KT  45 MPH
 60H  17/1800Z 18.2N 132.8W   35 KT  40 MPH...POST-TROPICAL
 72H  18/0600Z 18.3N 135.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  19/0600Z 18.5N 142.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  20/0600Z 18.4N 148.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Kelly/Berg
 
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