[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 220248
TCDAT2

Hurricane Fiona Discussion Number  31
NWS National Hurricane Center Miami FL       AL072022
1100 PM EDT Wed Sep 21 2022

Just after the last advisory, a white ring in the Dvorak curve
completely surrounded the eye, with cloud-top temperatures as cold
as about -80 degrees Celsius.  These temperatures have warmed a bit
since then, and the eye is not as warm as it was.  A NOAA Hurricane
Hunter aircraft flew two passes through the eye and measured a peak
700-mb flight-level of 119 kt and SFMR winds of 100-105 kt, but
also found that Fiona's central pressure has fallen to 934 mb.
Given the pressure drop, and the fact that satellite intensity
estimates are not much lower than before, the initial intensity
remains 115 kt (but this could be a little generous).  The plane
also found that the 50- and 64-kt wind radii have increased in size.

Fiona is still moving just east of due north, or 010/9 kt.  The
hurricane is expected to accelerate toward the north-northeast
during the next 24 hours while located along the western periphery
of the Azores-Bermuda high.  After that time, an even faster motion
toward the northeast and north-northeast is forecast as a
progressive deep-layer trough moves off the northeastern U.S. coast
Thursday night and Friday, propelling Fiona toward Atlantic Canada
at speeds of 25-30 kt.  A slower northward motion is expected by 72
hours, with Fiona continuing across the Gulf of St. Lawrence and
Labrador, and then over the Labrador Sea by days 4 and 5.  The
track guidance is very tightly clustered, and the new NHC track
forecast is mainly an update of the previous prediction.

Little change, or perhaps some fluctuations, in intensity are
expected during the next 24 hours while Fiona remains over warm
waters of 29-30 degrees Celsius and in a generally low-shear
environment.  Shear increases substantially in 36-48 hours, which
should cause some gradual weakening, and extratropical transition
due to the aforementioned trough is expected to be complete just
after 48 hours as the center of Fiona is approaching Nova Scotia.
The extratropical low is forecast to continue producing
hurricane-force winds as it crosses Nova Scotia and moves into the
Gulf of St. Lawrence through day 3, and it is expected to continue
producing gale-force winds as it moves across Newfoundland and
Labrador.  The NHC intensity forecast is close to the IVCN and HCCA
consensus aids during Fiona's tropical phase through 48 hours.
After that time, the official forecast more closely follows the GFS
and ECMWF global models solutions.

Based on the NOAA Hurricane Hunter data, the wind radii have been
expanded at the initial time and within the forecast.


Key Messages:

1. Hurricane conditions are possible, and tropical storm conditions
are expected, on Bermuda beginning Thursday evening and continuing
through Friday morning.

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 becoming increasingly likely.  Interests in these
areas should closely monitor the progress of Fiona and updates to
the forecast.

3. Large swells generated by Fiona are expected to cause dangerous
and possibly life-threatening surf and rip current conditions along
the east coast of the United States, the Bahamas, Bermuda, and
Atlantic Canada during the next few days.  Please consult products
from your local weather office.


FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 26.6N  71.2W  115 KT 130 MPH
 12H  22/1200Z 28.2N  70.5W  115 KT 130 MPH
 24H  23/0000Z 30.9N  68.7W  115 KT 130 MPH
 36H  23/1200Z 34.8N  65.1W  110 KT 125 MPH
 48H  24/0000Z 40.7N  61.7W  105 KT 120 MPH
 60H  24/1200Z 45.7N  61.4W   85 KT 100 MPH...POST-TROP/EXTRATROP
 72H  25/0000Z 48.5N  61.3W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  26/0000Z 54.9N  59.8W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  27/0000Z 62.2N  58.6W   30 KT  35 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg
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