[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 150856
TCDAT2

Tropical Storm Fiona Discussion Number   4
NWS National Hurricane Center Miami FL       AL072022
500 AM AST Thu Sep 15 2022

The satellite presentation of Fiona has not changed much overnight.
The low-level center of the storm is still displaced to the west of
a deep convective mass with very cold infrared cloud tops. Earlier
scatterometer data showed a broad area of tropical-storm-force winds
over the eastern portion of the circulation, with reliable peak
winds in the 40-45 kt range. Therefore, the initial intensity is
held at 45 kt for this advisory. An Air Force Hurricane Hunter
aircraft is scheduled to investigate Fiona later today.

Fiona is moving westward at 270/11 kt. The cyclone is expected to
generally maintain a westward heading for the next few days as it is
steered by the subtropical ridge over the central Atlantic. However,
there are still significant along-track differences among some of
the model solutions, with the GFS and ECMWF almost 250 n mi apart at
72 h. The latest NHC track forecast lies slightly south of the
previous one and is a bit slower through the first 72 h, remaining
closer to the latest GFEX and HCCA aids. This track brings Fiona
across the northern Leeward Islands by Friday night, near the Virgin
Islands and Puerto Rico this weekend, and near Hispaniola early next
week. From there, the deterministic guidance and most GFS and ECMWF
ensemble members agree that Fiona should turn northwestward by days
4-5 as a weakness develops in the steering ridge over the western
Atlantic. The stronger GFS and HWRF runs show a sharper recurvature
than the rest of the guidance, but the NHC forecast shows a more
gradual turn generally in line with the HCCA aid.

The sheared, asymmetric structure of Fiona does not appear conducive
for much strengthening in the near term. In fact, the SHIPS guidance
suggests that moderate to strong westerly to northwesterly shear
will persist for the next several days over Fiona. This, combined
with some drier mid-level air to the west of the storm, could make
it difficult for Fiona's inner-core structure to become better
organized. The intensity forecast is also complicated by the
potential for land interaction as the storm moves near or over
portions of the Greater Antilles this weekend and early next week.
Given the less-than-ideal conditions, the official NHC intensity
forecast does not show much strengthening over the next several
days, and it lies slightly below the intensity consensus aids.

Additional tropical storm watches or warnings will likely be
required later today for portions of the northern Leeward Islands,
Puerto Rico, and the Virgin Islands, and interests in these
locations should monitor the latest forecast updates.


Key Messages:

1. Tropical storm conditions are possible in portions of the
northern Leeward Islands by Friday night, where a Tropical Storm
Watch has been issued.

2. Heavy rains from Fiona will reach the northern Leeward Islands
Friday afternoon, spreading to the British and U.S. Virgin Islands
and Puerto Rico Saturday into Sunday morning, and reaching eastern
Hispaniola Sunday. This rainfall may produce flash and urban
flooding, along with isolated mudslides in areas of higher terrain.

3. Fiona is expected to move near the Virgin Islands, Puerto Rico,
and Hispaniola this weekend and early next week, and Tropical Storm
Watches will likely be issued for some of those areas later today.


FORECAST POSITIONS AND MAX WINDS

INIT  15/0900Z 16.6N  53.0W   45 KT  50 MPH
 12H  15/1800Z 16.7N  54.7W   45 KT  50 MPH
 24H  16/0600Z 16.8N  57.3W   50 KT  60 MPH
 36H  16/1800Z 17.0N  59.8W   50 KT  60 MPH
 48H  17/0600Z 17.2N  62.3W   50 KT  60 MPH
 60H  17/1800Z 17.4N  64.4W   50 KT  60 MPH
 72H  18/0600Z 17.7N  66.1W   50 KT  60 MPH
 96H  19/0600Z 18.8N  68.6W   50 KT  60 MPH
120H  20/0600Z 21.0N  70.5W   55 KT  65 MPH

$$
Forecaster Reinhart
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