[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 100841
TCDAT1

Hurricane Earl Discussion Number  30
NWS National Hurricane Center Miami FL       AL062022
500 AM AST Sat Sep 10 2022

Earl is in the first stages of extratropical transition.  The
convective cloud pattern is becoming stretched east to west, and
the eye is rapidly losing definition while an extensive cirrus
shield radiates northward away from the hurricane.  Scatterometer
data from last evening showed that Earl's wind field continues to
expand and was beginning to merge with the strong winds behind an
approaching frontal boundary.  Maximum winds are still estimated to
be 90 kt based on a blend of Dvorak data-T and Current Intensity
numbers from TAFB and SAB, as well as the UW-CIMSS ADT.

The hurricane continues to accelerate just ahead of a shortwave
trough and is estimated to be moving rapidly northeastward (035
degrees) at 30 kt.  However, Earl will be merging with this trough
within the next 6 to 12 hours, which will cause it to slam on the
brakes southeast of Newfoundland, slowing to speeds of 5 kt or less
beginning tonight and continuing through Monday.  After Monday, a
less amplified upper-level pattern should cause the system to turn
eastward and pick up some speed.  The updated NHC track forecast
has been shifted a bit northwestward during the first couple of
days of the forecast and lies within the tightly packed guidance
envelope.  The NHC prediction then comes back in line with
the previous forecast on days 3 through 5.  The northwestward
shift of the track, along with Earl's large wind field, is expected
to lead to strong winds occurring over the Avalon Peninsula of
Newfoundland beginning this afternoon and continuing through
Sunday.  For additional information on impacts in Newfoundland,
please monitor forecasts and warnings from Environment Canada.

Global model fields show Earl's center migrating into the cold side
of the nearby frontal zone today, with extratropical transition
forecast to be complete this afternoon.  This process, along with
Earl now crossing the tight sea surface temperature gradient north
of the Gulf Stream, is expected to induce a weakening trend, with
the cyclone's winds likely falling below hurricane force by
tonight.  Continued weakening at a more gradual pace is anticipated
from Sunday onward into the middle of the week.  The NHC intensity
forecast most closely follows the GFS and ECMWF solutions given
that Earl will soon be extratropical.


KEY MESSAGES:

1. Strong winds are expected over the Avalon Peninsula of
Newfoundland beginning this afternoon and continuing through Sunday,
after Earl becomes a post-tropical low.

2. Large swells generated by Earl will affect Bermuda, portions
of the U.S. East Coast, and Nova Scotia and Newfoundland during the
next several days.  These swells are likely to cause
life-threatening surf and rip current conditions.  Please consult
products from your local weather office.


FORECAST POSITIONS AND MAX WINDS

INIT  10/0900Z 41.2N  53.5W   90 KT 105 MPH
 12H  10/1800Z 43.2N  52.1W   75 KT  85 MPH...POST-TROP/EXTRATROP
 24H  11/0600Z 44.1N  51.3W   60 KT  70 MPH...POST-TROP/EXTRATROP
 36H  11/1800Z 44.5N  50.6W   50 KT  60 MPH...POST-TROP/EXTRATROP
 48H  12/0600Z 44.7N  50.1W   45 KT  50 MPH...POST-TROP/EXTRATROP
 60H  12/1800Z 44.8N  48.8W   40 KT  45 MPH...POST-TROP/EXTRATROP
 72H  13/0600Z 44.7N  46.4W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  14/0600Z 44.9N  41.5W   35 KT  40 MPH...POST-TROP/EXTRATROP
120H  15/0600Z 45.3N  37.4W   35 KT  40 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg
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