[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 200253
TCDAT2

Hurricane Fiona Discussion Number  23
NWS National Hurricane Center Miami FL       AL072022
1100 PM EDT Mon Sep 19 2022

The satellite presentation of the hurricane has improved
significantly this evening.  The eye has warmed and become more
distinct and the surrounding ring of deep convection has cooled and
is more symmetric.  More recently, the eye has become smaller in
size and this has also been observed by both NOAA and Air Force
Reserve Hurricane Hunter aircraft that have been sampling the storm
this evening. The aircraft have reported that the eye has shrunk to
around 10 n mi in diameter.  The NOAA plane has measured a peak
flight level wind of 104 kt at around 8000 ft, while the Air Force
aircraft has reported a peak 700-mb flight-level wind of 93 kt.
Peak SFMR winds of 94-96 kt have also been found, and these data
support increasing the initial intensity to 95 kt.

The hurricane's outflow is somewhat restricted over the western
portion of the circulation owing to some moderate southwesterly
shear of the storm.  Although this shear is not forecast to abate
much, the intensity guidance indicates that warm water and a moist
atmosphere should allow for continued intensification during the
next 24 to 48 hours.  Given the recent improvement in structure,
the updated NHC intensity forecast calls for a slightly faster rate
of strengthening during the next 12 to 24 hours, and it is at the
upper end of the intensity guidance.  The official forecast shows
Fiona becoming a major hurricane overnight, and brings the
hurricane to category 4 status in a day or so.  Eyewall replacement
cycles are likely to cause some fluctuations in intensity in the
24-72 h time period.  By day 4, the hurricane is forecast to
interact with a strong mid-tropospheric trough, which will start
the system's extratropical transition.  The process is forecast to
be complete by the end of the period, and Fiona is expected to
remain a powerful extratropical cyclone through day 5.

The initial motion estimate is 330/9 kt. There track forecast
philosophy again remains the same as the previous few forecast
cycles. The hurricane should gradually turn north while moving
around the western periphery of a mid-level ridge. After 72 hours,
Fiona is forecast to turn north-northeastward and accelerate as a
strong mid-level trough nears the northeastern United States. The
track guidance remains tightly clustered and the NHC forecast is
similar to the previous advisory, near the middle of the guidance
envelope.

Key Messages:

1.  Heavy rains from Fiona will continue across parts of Puerto Rico
and across northern and eastern Dominican Republic through tonight.
These rainfall amounts will continue to produce life-threatening
and catastrophic flooding along with mudslides and landslides
across Puerto Rico. Life-threatening flash and urban flooding is
likely for eastern portions of the Dominican Republic.

2. Hurricane conditions are expected over the Turks and Caicos, with
tropical storm conditions over the southeastern Bahamas, beginning
late tonight or early Tuesday.

3.  Interests in Bermuda should monitor the progress of Fiona.


FORECAST POSITIONS AND MAX WINDS

INIT  20/0300Z 20.6N  70.3W   95 KT 110 MPH
 12H  20/1200Z 21.8N  71.0W  110 KT 125 MPH
 24H  21/0000Z 23.3N  71.4W  115 KT 130 MPH
 36H  21/1200Z 24.6N  71.4W  120 KT 140 MPH
 48H  22/0000Z 26.3N  71.0W  120 KT 140 MPH
 60H  22/1200Z 28.5N  69.9W  120 KT 140 MPH
 72H  23/0000Z 31.1N  68.0W  115 KT 130 MPH
 96H  24/0000Z 39.8N  60.7W  105 KT 120 MPH
120H  25/0000Z 49.7N  58.5W   65 KT  75 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown
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