[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 180856
TCDAT2

Tropical Storm Fiona Discussion Number  16
NWS National Hurricane Center Miami FL       AL072022
500 AM AST Sun Sep 18 2022

Fiona has continued to show signs of better organization in Doppler
radar data from San Juan this morning, and earlier data from an Air
Force Hurricane Hunter aircraft indicate that the storm has indeed
strengthened. The aircraft reported peak flight-level (700 mb) winds
of 57 kt, along with several instances of SFMR winds greater than 50
kt and a peak of 57 kt in the northeastern quadrant of the storm.
Also, a center dropsonde indicated that the minimum pressure had
fallen a few millibars to 994 mb. Based on these data, the initial
intensity is raised to 55 kt for this advisory.

After a brief northward jog last night, the center of Fiona appears
to have resumed a more west-northwestward heading (290/7 kt). The
storm is expected to turn northwestward later today, which should
bring the center of Fiona near or over the southwestern portion of
Puerto Rico this afternoon and near the northern coast of the
Dominican Republic early Monday. Then, a mid-level trough over the
southwestern Atlantic is forecast to induce a weakness in the
steering ridge early next week. This should enable Fiona to turn
slowly northward by midweek while it passes near or to the east of
the Turks and Caicos Islands. An acceleration to the north and
north-northeast is forecast by late in the week as Fiona moves
within the flow ahead of an amplifying mid- to upper-level trough.
The models are tightly clustered throughout the forecast period and
no major changes were made to the NHC track forecast, which still
lies close to the consensus aids near the center of the guidance
envelope.

Moderate southwesterly to westerly shear appears likely to continue
affecting Fiona during the next several days. However, very warm
sea-surface temperatures and sufficient mid-level moisture are still
expected to allow for some intensification as Fiona approaches
Puerto Rico and the Dominican Republic. The NHC forecast calls for
Fiona to become a hurricane later today before it moves near or over
Puerto Rico. Once the cyclone moves away from land and reaches the
southwestern Atlantic, more significant strengthening is forecast in
agreement with the consensus of the intensity guidance. The latest
NHC intensity forecast has been raised from 48 h through the end of
the forecast period, but still lies slightly below the IVCN and HCCA
aids. Fiona could reach major hurricane strength by late this week
over the western Atlantic.


Key Messages:

1.  Hurricane conditions are expected across portions of Puerto Rico
today, and are expected in portions of the Dominican Republic
tonight and Monday. Tropical storm conditions are occurring across
the U.S. and British Virgin Islands and are spreading westward
across Puerto Rico. Tropical storm conditions will reach the
Dominican Republic later today and tonight.

2. Heavy rains from Fiona will continue across Puerto Rico through
tonight and occur over the Dominican Republic later today into
Monday. These rainfall amounts will produce life-threatening flash
floods and urban flooding across Puerto Rico and portions of the
eastern Dominican Republic, along with mudslides and landslides in
areas of higher terrain.

3. Fiona is forecast to strengthen after moving away from Puerto
Rico and the Dominican Republic. Tropical storm conditions are
possible in the Turks and Caicos Islands and the southeastern
Bahamas by late Monday or early Tuesday, and a Tropical Storm Watch
has been issued for these locations.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 17.1N  65.8W   55 KT  65 MPH
 12H  18/1800Z 17.8N  66.9W   65 KT  75 MPH
 24H  19/0600Z 18.7N  68.0W   65 KT  75 MPH
 36H  19/1800Z 19.8N  69.0W   70 KT  80 MPH
 48H  20/0600Z 21.2N  69.8W   80 KT  90 MPH
 60H  20/1800Z 22.6N  70.5W   85 KT 100 MPH
 72H  21/0600Z 23.9N  70.7W   90 KT 105 MPH
 96H  22/0600Z 27.5N  70.0W   95 KT 110 MPH
120H  23/0600Z 33.0N  66.0W   95 KT 110 MPH

$$
Forecaster Reinhart
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