[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 180253
TCDAT2

Tropical Storm Fiona Discussion Number  15
NWS National Hurricane Center Miami FL       AL072022
1100 PM AST Sat Sep 17 2022

Satellite imagery and Doppler radar data from San Juan indicate that
Fiona is gradually becoming better organized, with the radar showing
increasing banding near the center and a possible decrease in the
radius of maximum winds.  However, this has not yet resulted in any
increase in intensity, with the radar winds and data from an Air
Force Reserve Hurricane Hunter aircraft suggesting that the maximum
sustained winds remain near 50 kt.  The aircraft has reported that
the central pressure has fallen to 997 mb.

Fiona's motion has been a bit erratic over the past few hours.
However, the longer-term motion is a somewhat uncertain 285/7 kt. A
turn toward the northwest is expected in about 12 h, with a general
northwestward motion continuing through about 48 h as Fiona is
steered by the subtropical ridge to the northeast.  After that, the
cyclone is expected to move slowly northward through a break in the
ridge caused by a mid- to upper-level trough over the Florida
Peninsula and the adjacent Atlantic.  By the end of the forecast
period, a north-northeastward motion at a faster forward speed is
expected as Fiona reaches the southern edge of the mid-latitude
westerlies.  The new forecast track is similar to the previous track
and to the consensus models, with the center forecast to move near
the southwestern portion of Puerto Rico and the northern coast of
the Dominican Republic before passing east of the Turks and Caicos
Islands.

While the vertical wind shear has diminished since yesterday, Fiona
remains in an environment of moderate southwesterly shear, and the
model guidance suggests that this is likely to persist through the
forecast period.  This will limit the intensification, although the
storm will pass over warm sea surface temperatures and move into a
more moist environment.  The new intensity forecast calls for Fiona
to reach hurricane strength in about 24 h as it passes near Puerto
Rico.  After that, development could be interrupted by close
proximity to the Dominican Republic. More earnest strengthening
appears likely when Fiona moves away from land after 48 h, and the
intensity forecast again calls for a peak intensity of 95 kt.  It
should be noted that the intensity guidance has a large amount of
spread, and there are models both stronger and weaker than the
official forecast.


Key Messages:

1.  Hurricane conditions are expected across portions of Puerto Rico
on Sunday, and are expected in portions of the Dominican Republic
Sunday night and Monday.  Hurricane conditions 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 tonight.  Tropical storm conditions
will reach the Dominican Republic by late Sunday.

2. Heavy rains from Fiona will continue to spread west across the
British and U.S. Virgin Islands and Puerto Rico tonight, 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
portions of the eastern 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  18/0300Z 16.6N  64.9W   50 KT  60 MPH
 12H  18/1200Z 17.2N  66.0W   60 KT  70 MPH
 24H  19/0000Z 18.1N  67.3W   65 KT  75 MPH
 36H  19/1200Z 19.1N  68.5W   65 KT  75 MPH
 48H  20/0000Z 20.3N  69.4W   70 KT  80 MPH
 60H  20/1200Z 21.6N  70.2W   75 KT  85 MPH
 72H  21/0000Z 23.0N  70.5W   80 KT  90 MPH
 96H  22/0000Z 25.5N  70.5W   90 KT 105 MPH
120H  23/0000Z 31.0N  67.5W   95 KT 110 MPH

$$
Forecaster Beven
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