[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 172057
TCDAT2

Tropical Storm Fiona Discussion Number  14
NWS National Hurricane Center Miami FL       AL072022
500 PM AST Sat Sep 17 2022

After going through a bit of a re-organization this morning,
Fiona's structure appears to be improving again.  Visible satellite
images show an elongated band of deep convection wrapping around
the center from north to east to southwest, and WSR-88D Doppler
radar from San Juan, Puerto Rico, suggests that a better-defined
center of circulation has developed.  A 1707 UTC AMSR-2 microwave
pass also shows that a mid-level eye feature may be developing.
The last Air Force Reserve reconnaissance mission from a few hours
ago found that the central pressure had fallen back down to 1002 mb,
but maximum winds still appeared to be around 50 kt.  The next
reconnaissance mission is scheduled for this evening.

Fiona's motion today has been discontinuous due to the storm's
center re-formation, but the smoothed longer-term motion is now
west-northwestward, or 285/8 kt.  This general motion is expected
to continue through tonight, with Fiona expected to turn
northwestward on Sunday as it begins to move around the western
periphery of the subtropical ridge.  A turn toward the
north-northwest is expected by Monday night, followed by a
northward and north-northeastward acceleration over the western
Atlantic by Thursday.  In general, the new NHC forecast is close to
the TVCN and HCCA consensus aids, in the middle of the guidance
envelope.  This prediction is a little bit north of this morning's
forecast during the first 24 to 36 hours, mainly accounting for
Fiona's adjusted initial position.  After 36 hours, the track
forecast is not too different from earlier.

Since the new track forecast has the center of Fiona reaching
Puerto Rico in about 24 hours, the window for strengthening is less
than it was earlier today.  However, the NHC intensity forecast is
near the IVCN and HCCA consensus aids and suggests that Fiona will
be at or near hurricane intensity before moving across Puerto Rico
on Sunday.  If the center does cross Puerto Rico, that could halt
intensification, or cause some slight weakening, but Fiona is
expected to go through a more significant strengthening phase once
it's over the western Atlantic.  The forecast shows Fiona just
below major hurricane intensity by day 5, although it should be
mentioned that this prediction is slightly below the consensus aids.


Key Messages:

1.  Hurricane conditions are expected across portions of Puerto
Rico on Sunday, and are possible across the U.S. Virgin Islands
tonight.  Tropical storm conditions are now spreading westward
across the U.S. and British Virgin Islands and will spread
across Puerto Rico this evening and tonight.  Tropical storm
conditions will reach the Dominican Republic by late Sunday.

2. Heavy rains from Fiona will spread west to the British and U.S.
Virgin Islands and Puerto Rico today, the Dominican Republic Sunday,
and the Turks and Caicos Monday night. These rainfall amounts are
expected to produce life-threatening flash floods and urban
flooding, along with mudslides in areas of higher terrain,
especially across portions of Puerto Rico and the Dominican
Republic.

3. Fiona is forecast to strengthen after moving away from Puerto
Rico and past the Dominican Republic on Monday, and interests in the
Turks and Caicos Islands and southeastern Bahamas should continue to
monitor forecasts for the storm.


FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 16.7N  64.6W   50 KT  60 MPH
 12H  18/0600Z 17.3N  65.5W   60 KT  70 MPH
 24H  18/1800Z 18.1N  66.7W   65 KT  75 MPH...OVER PUERTO RICO
 36H  19/0600Z 19.0N  68.0W   65 KT  75 MPH...OVER WATER
 48H  19/1800Z 20.1N  69.0W   70 KT  80 MPH
 60H  20/0600Z 21.4N  69.8W   75 KT  85 MPH
 72H  20/1800Z 22.7N  70.5W   80 KT  90 MPH
 96H  21/1800Z 25.4N  70.7W   90 KT 105 MPH
120H  22/1800Z 29.9N  68.8W   95 KT 110 MPH

$$
Forecaster Berg
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