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TROPICAL STORM FIONA DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
1100 AM AST SAT AUG 20 2016

Fiona is fighting off southwesterly shear this morning as the center
has become embedded under the southwestern side of an area of deep
convection.  The Dvorak estimates from TAFB and SAB have held
steady, so the initial intensity is held at 35 kt.  Although a
recent ASCAT overpass missed the center of Fiona, the pass did show
30-kt winds more than 50 n mi east of the center, suggesting that
tropical-storm-force winds could be occurring closer to the center
of circulation. Strong southwesterly shear of 25 to 30 kt is
forecast to persist during the next few days. These unfavorable
conditions combined with dry air along the path of the cyclone
should induce a gradual weakening trend, and Fiona is expected to
weaken to a tropical depression by tonight or early Sunday morning.
The ECMWF and UKMET models continue to open this system into a
trough within 3 days, whereas, the other model guidance lessens the
shear slightly toward the end of the 5-day period and allows Fiona
to survive for the next several days. The official forecast is
similar to the previous one, and leans toward the ECMWF and UKMET
model solutions.

The initial position of Fiona is located slightly to the north of
the previous forecast track, based on recent microwave data. The
track forecast reasoning remains unchanged, as the low- to mid-level
subtropical ridge over the central Atlantic should keep Fiona moving
west-northwestward for the next several days.  There remains a fair
amount of spread in the guidance, which appears largely dependent
on the future strength and status of the cyclone.  The NHC track
forecast lies on the western side of guidance, except for the short
term forecast positions where a slight adjustment to the north was
made due to the initial position and motion.

FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 20.3N  47.8W   35 KT  40 MPH
 12H  21/0000Z 21.2N  49.5W   35 KT  40 MPH
 24H  21/1200Z 22.3N  52.1W   30 KT  35 MPH
 36H  22/0000Z 23.3N  54.8W   30 KT  35 MPH
 48H  22/1200Z 24.2N  57.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  23/1200Z 26.2N  61.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  24/1200Z 28.2N  63.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  25/1200Z...DISSIPATED

$$
Forecaster Cangialosi/Latto

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