[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 160858
TCDAT2

Tropical Storm Fiona Discussion Number   8
NWS National Hurricane Center Miami FL       AL072022
500 AM AST Fri Sep 16 2022

Fiona remains a sheared tropical cyclone this morning. The center of
the storm is fully exposed to the west of a large area of deep
convection over much of the eastern portion of the circulation. An
Air Force Reserve Hurricane Hunter aircraft that investigated Fiona
found peak 925 mb flight-level winds of 60 kt, which would support a
surface wind of about 45 kt using a standard reduction factor.
Meanwhile, the SFMR data only supported surface winds of 35-40 kt.
Earlier scatterometer data showed an area of winds slightly above 40
kt in the northeastern quadrant of the storm. Based on these data,
the initial intensity is set at 45 kt for this advisory.

The latest aircraft fixes indicate that Fiona is still moving south
of due west, and its initial motion is estimated to be 260/13 kt.
The models agree that Fiona should move generally westward over the
next couple of days, to the south of the subtropical ridge across
the central and western Atlantic. This brings the center of the
storm across the Leeward Islands tonight and near the Virgin Islands
and Puerto Rico on Saturday through early Sunday. Then, a turn
toward the west-northwest and northwest is forecast as the storm
reaches a weakness in the steering ridge. This would bring the
center of Fiona near or over Hispaniola on Monday and then into the
southwestern Atlantic by days 4-5. The NHC track forecast has once
again been adjusted slightly south of the previous one in the near
term, but generally lies near the center of the guidance envelope on
days 3-5.

Some short-term intensity fluctuations are possible given the
sheared, asymmetric structure of the storm. However, there are some
indications that the environmental conditions could become more
conducive for strengthening as the storm moves into the eastern
Caribbean this weekend. In particular, increasing upper-level
divergence and mid-level moisture along with decreasing vertical
wind shear could allow Fiona to become better organized before it
reaches Hispaniola. The latest NHC intensity forecast shows a bit
more strengthening through 72 h, but still lies slightly below the
guidance consensus. From there, the intensity forecast is of lower
confidence as the extent of land interaction is still uncertain.


Key Messages:

1. Tropical storm conditions are expected in the Leeward Islands
within the warning area by this evening. Tropical storm conditions
are possible within the watch area across the Virgin Islands
beginning on Saturday, and then reaching Puerto Rico late Saturday
and Saturday night.

2. Heavy rains from Fiona will reach the Leeward Islands by this
evening, spreading to the British and U.S. Virgin Islands and Puerto
Rico Saturday, reaching the Dominican Republic Sunday, and the Turks
and Caicos Monday night or Tuesday. This rainfall may produce
considerable flood impacts including flash and urban flooding, along
with mudslides in areas of higher terrain.

3. Fiona is expected to move near Hispaniola early next week, and
watches could be required for parts of the island later today.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0900Z 15.7N  58.1W   45 KT  50 MPH
 12H  16/1800Z 15.9N  60.0W   50 KT  60 MPH
 24H  17/0600Z 16.3N  62.5W   50 KT  60 MPH
 36H  17/1800Z 16.7N  64.6W   55 KT  65 MPH
 48H  18/0600Z 17.0N  66.3W   55 KT  65 MPH
 60H  18/1800Z 17.3N  67.8W   60 KT  70 MPH
 72H  19/0600Z 18.1N  69.2W   60 KT  70 MPH
 96H  20/0600Z 20.0N  71.0W   55 KT  65 MPH
120H  21/0600Z 22.0N  72.5W   60 KT  70 MPH

$$
Forecaster Reinhart
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