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TROPICAL STORM FIONA DISCUSSION NUMBER  20
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
500 PM AST SUN AUG 21 2016

Deep convection continues to pulsate over the northern and eastern
portions of Fiona's circulation.  However, there is very little
banding evident and the cloud tops are being advected quickly
eastward due to strong upper-level westerly winds over the cyclone.
This morning's ASCAT data that arrived just after the release of the
previous advisory indicated peak winds of 35 kt, which was in line
with the the earlier intensity estimate.  Since there has been
little change in organization today, the initial wind speed will
remain 35 kt for this advisory.  Strong westerly shear is forecast
to persist during the next day or so.  This, combined with dry
mid-level air, should result in weakening, and Fiona is expected to
weaken to a tropical depression during the next 24 hours, and become
a remnant low in a couple of days.  If Fiona or its remnants survive
the next few days, conditions could become somewhat conducive for
regeneration or restrengthening later in the forecast period.  The
latest runs of GFS and UKMET models continue to maintain a weak low
through the 5-day forecast period, whereas the ECMWF shows
dissipation in 2 to 3 days.  The NHC forecast continues to maintain
continuity, and indicates dissipation by day 5.

Fiona continues to move quickly west-northwestward to the south of a
low- to mid-level ridge over the central Atlantic.  The cyclone will
be nearing the western portion of the ridge in a couple of days,
which is expected to cause Fiona to slow down.  After 72 hours,
Fiona, or its remnants, should turn northwestward around the western
portion of the ridge.  Due to model differences in the strength and
depth of Fiona after 48 hours, the spread in the track guidance is
quite large beyond 3 days.  The updated NHC track is near the multi-
model consensus, which is closer to the GFS and GFS ensemble mean
solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 23.4N  54.9W   35 KT  40 MPH
 12H  22/0600Z 23.9N  57.0W   35 KT  40 MPH
 24H  22/1800Z 24.7N  59.5W   30 KT  35 MPH
 36H  23/0600Z 25.4N  61.5W   30 KT  35 MPH
 48H  23/1800Z 26.3N  63.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  24/1800Z 28.4N  66.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  25/1800Z 30.5N  67.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  26/1800Z...DISSIPATED

$$
Forecaster Brown

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