[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 220232
TCDAT1

TROPICAL DEPRESSION FIONA DISCUSSION NUMBER  21
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
1100 PM AST SUN AUG 21 2016

Deep convection continues to sputter near the center of Fiona, with
each successive burst a little smaller and less organized than the
previous ones that sheared off in the strong westerly upper-level
winds.  Given that earlier ASCAT data only showed a few 35-kt winds
and the decrease in convective organization since that time, the
initial intensity is set to 30 kt, which is also in agreement with
the latest TAFB Dvorak estimate.

The intensity forecast remains tricky.  Fiona has been slowly
weakening due to about 30 kt of westerly wind shear and mid-level
dry air, and the NHC forecast shows the cyclone becoming a remnant
low in the next 24 to 36 hours.  However, the shear is forecast to
decrease to 10 kt or less by 48 hours and the mid-levels begin to
moisten according to the SHIPS model forecast.  Therefore, if Fiona
can survive the next 24 to 36 hours, the environment will become
more conducive for restrengthening or maintaining the system as a
tropical cyclone.  The global models still disagree on the fate of
Fiona, with the ECMWF showing dissipation in 2-3 days while the GFS
and UKMET keep Fiona as a weak low through 5 days.  The NHC forecast
maintains continuity and indicates dissipation in 5 days as a
compromise between these possibilities.

The initial motion estimate is 290/16, as Fiona continues to move
quickly west-northwestward under the influence of a low- to mid-
level ridge over the central Atlantic.  Fiona, or its remnants, will
move around the western side of the ridge during the next several
days, which should result is a poleward turn and a decrease in
forward speed.  The new NHC forecast is largely an update of the
previous one through dissipation.  There continues to be a fair
amount of cross-track spread late in the period, and the NHC track
still favors the GFS solution and lies to the right of the multi-
model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 23.8N  56.6W   30 KT  35 MPH
 12H  22/1200Z 24.5N  58.6W   30 KT  35 MPH
 24H  23/0000Z 25.3N  60.9W   30 KT  35 MPH
 36H  23/1200Z 26.2N  62.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  24/0000Z 27.0N  64.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  25/0000Z 29.0N  67.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  26/0000Z 30.5N  68.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  27/0000Z...DISSIPATED

$$
Forecaster Brennan
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