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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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