Tropical Storm Fiona Forecast Discussion Number 15

By | September 18, 2022

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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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