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Tropical Storm Fernanda Discussion Number   3
NWS National Hurricane Center Miami FL       EP072023
200 AM PDT Sun Aug 13 2023
 
Geostationary satellite imagery shows that banding associated with 
Fernanda has continued to increase overnight with a small central 
dense overcast feature recently developing.  Unfortunately there 
have been no recent microwave or scatterometer overpasses to help 
ascertain the inner core structure and wind field of the small 
tropical cyclone.  The latest subjective Dvorak estimates range 
from T2.5  (35 kt) from TAFB to T3.5 (55 kt) from SAB.  The initial 
intensity for this advisory is set at 45 kt, using a blend of those 
subjective estimates. 

Fernanda is currently traversing SSTs of around 29 degrees Celsius 
and is within an area of low vertical wind shear  These conditions 
favor steady to rapid strengthening during the next 24 to 36 hours.  
The only negative factor is some nearby dry mid-level air, but the 
low shear conditions suggest that the small cyclone is likely to 
intensify.  Although the NHC intensity forecast does not quite 
predict rapid strengthening during the next 24 hours, it does 
forecast a fairly substantial 40 kt increase in wind speed during 
the next 36 hours, showing rapid intensification (RI) between the 
12 and 36 hour period.  After 60 hours, decreasing SSTs and a more 
stable environment along the track of Fernanda are expected to 
cause steady weakening later in the period.  The latest NHC 
intensity forecast is a little above the SHIPS guidance, but lies 
near the ICON consensus aid.  This is a little below the latest 
HFIP corrected consensus model. 

The tropical storm is moving west-northwestward at about 9 kt.  A 
westward to west-northwestward motion is expected to continue 
during the next few days at a slightly slower forward speed.  After 
that time, a faster westward motion is anticipated as the ridge to 
the north of Fernanda strengthens.  There is some cross-track 
spread in the guidance beyond 72 hours which is primarily related 
to how much latitude Fernanda gains during the next few days. 
The NHC track prediction is near the middle of the guidance 
envelope, close to a blend of the GFS and ECMWF models. 


FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0900Z 15.1N 115.1W   45 KT  50 MPH
 12H  13/1800Z 15.3N 116.4W   55 KT  65 MPH
 24H  14/0600Z 15.6N 118.0W   70 KT  80 MPH
 36H  14/1800Z 16.0N 119.7W   85 KT 100 MPH
 48H  15/0600Z 16.5N 121.2W   85 KT 100 MPH
 60H  15/1800Z 17.0N 123.1W   80 KT  90 MPH
 72H  16/0600Z 17.3N 125.5W   70 KT  80 MPH
 96H  17/0600Z 17.6N 130.8W   50 KT  60 MPH
120H  18/0600Z 17.7N 137.0W   35 KT  40 MPH
 
$$
Forecaster Brown
 
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