[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 212039
TCDAT2

Hurricane Fiona Discussion Number  30
NWS National Hurricane Center Miami FL       AL072022
500 PM EDT Wed Sep 21 2022

Fiona continues to have a fairly impressive presentation on
satellite images, although the eye has become partially cloud-
filled.  The central convection continues to have very cold cloud
tops to near -80 deg C,  and the Central Dense Overcast is
surrounded by numerous banding features, especially over the
eastern semicircle.  Upper-tropospheric outflow is strong over the
northern and eastern portions of the circulation.  The current
intensity is held at 115 kt, i.e. Category 4, in agreement with a
subjective Dvorak estimate from SAB.

The hurricane should remain over warm waters for the next 48 hours,
and in a moist and unstable air mass.  Some strengthening is still
possible within the next day or so.  Eyewall replacement cycles
could cause some intensity fluctuations, but these are difficult to
predict.  Fiona is expected to interact with a strong
mid-tropospheric trough moving off the northeastern United States
coast in around 60 hours.  This interaction should lead to the
system transforming into an intense extratropical cyclone, with
hurricane-force winds, before it reaches Atlantic Canada.

Fiona's motion is beginning to show signs of a turn toward the
north-northeast as the eye has been leaning toward the right
over the past few hours.  The initial motion is just east of
north or about 010/8 kt.  There are no significant changes to the
track forecast or its reasoning.  During the next 12 to 24
hours, the hurricane is expected to move northward to
north-northeastward along the western periphery of a mid-level
subtropical high pressure area.  Thereafter, Fiona is forecast to
gradually accelerate northeastward to north-northeastward in
the flow ahead of the aforementioned trough.  The official track
forecast remains close to both the simple and corrected
dynamical model consensus, TVCN and HCCA, respectively.

Based on an earlier ASCAT overpass, the wind radii have been
expanded.  The model guidance indicates that Fiona will grow even
larger in size during the next few days.

Key Messages:

1. Hurricane conditions are possible, and tropical storm conditions
are expected, on Bermuda by late tomorrow.

2. Fiona is expected to affect portions of Atlantic Canada as a
powerful hurricane-force cyclone late Friday and Saturday, and could
produce significant impacts from high winds, storm surge, and heavy
rainfall. Interests in these areas should closely monitor the
progress of Fiona and updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 25.6N  71.5W  115 KT 130 MPH
 12H  22/0600Z 27.0N  71.0W  120 KT 140 MPH
 24H  22/1800Z 29.5N  69.6W  120 KT 140 MPH
 36H  23/0600Z 32.6N  66.9W  115 KT 130 MPH
 48H  23/1800Z 37.4N  63.0W  110 KT 125 MPH
 60H  24/0600Z 43.5N  61.1W   90 KT 105 MPH...POST-TROP/EXTRATROP
 72H  24/1800Z 47.0N  61.0W   75 KT  85 MPH...POST-TROP/EXTRATROP
 96H  25/1800Z 52.5N  60.5W   45 KT  50 MPH...POST-TROP/EXTRATROP
120H  26/1800Z 60.0N  59.1W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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