[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 230257
TCDAT2

Hurricane Fiona Discussion Number  35
NWS National Hurricane Center Miami FL       AL072022
1100 PM AST Thu Sep 22 2022

Fiona's satellite appearance looks a little more asymmetric this
evening, with deep convection and upper-level outflow becoming more
restricted on the western side.  That said, the hurricane has not
yet lost any intensity.  An Air Force Reserve Hurricane Hunter
mission measured a peak 700-mb flight-level wind of 123 kt and SFMR
winds as high as 110 kt, which support maintaining a 115-kt
intensity on this advisory.  In addition, dropsonde data indicate
that the central pressure has fallen further to 932 mb, and the
SFMR instrument measured hurricane-force winds now extending 100 n
mi to the southeast of the center.

The hurricane is still accelerating toward the north-northeast with
an initial motion estimate of 030/18 kt.  Fiona is getting closer
to a deep-layer trough currently located over the northeastern
United States, and this feature is expected to cause the hurricane
to speed up further during the next day or so, reaching peak speeds
of 30-35 kt by 24 hours as it approaches Nova Scotia.  Fiona should
merge with the trough soon after 24 hours, slow down a bit, but
continue moving northward across Atlantic Canada to the Labrador
Sea.  The previous official forecast appears on track based on the
latest guidance, and no significant changes were made to the new
forecast.

Fiona is forecast to remain over warm waters, including within the
Gulf Stream current, during the next 24 hours, although deep-layer
shear is forecast to increase substantially in 12-24 hours.  Given
the hurricane's current appearance, some gradual weakening is
anticipated during the next day or so.  Extratropical transition
should begin on Friday, and that process is expected to be quick,
with Fiona becoming a warm-seclusion-type extratropical low Friday
night before the center reaches Nova Scotia.  Although continued
weakening is forecast thereafter, Fiona is expected to maintain
hurricane-force winds through 48 hours while it moves across the
Gulf of St. Lawrence.  Winds could drop below gale force by day 5
when the post-tropical low is over the Labrador Sea.  After 24
hours, the NHC intensity forecast is a blend of the GFS and ECMWF
global model solutions.


Key Messages:

1. Hurricane conditions are expected on Bermuda overnight.
Conditions should diminish below tropical storm force during the
day on Friday.

2. Fiona is expected to affect portions of Atlantic Canada as a
powerful hurricane-force cyclone late Friday and Saturday, and
significant impacts from high winds, storm surge, and heavy rainfall
are likely. Hurricane and Tropical Storm Warnings have now been
issued for much of Atlantic Canada.

3. Large swells generated by Fiona are expected to cause
life-threatening surf and rip current conditions along much of the
east coast of the United States, the Bahamas, Bermuda, and Atlantic
Canada during the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 31.9N  68.1W  115 KT 130 MPH
 12H  23/1200Z 34.8N  65.4W  110 KT 125 MPH
 24H  24/0000Z 40.9N  61.9W  105 KT 120 MPH
 36H  24/1200Z 45.8N  61.0W   90 KT 105 MPH...POST-TROP/EXTRATROP
 48H  25/0000Z 48.7N  60.1W   65 KT  75 MPH...POST-TROP/EXTRATROP
 60H  25/1200Z 52.2N  58.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 72H  26/0000Z 56.2N  57.9W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  27/0000Z 62.0N  57.7W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  28/0000Z 64.8N  56.2W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg
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