[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 081459
TCDAT1

Hurricane Earl Discussion Number  23
NWS National Hurricane Center Miami FL       AL062022
1100 AM AST Thu Sep 08 2022

The convective structure of Earl this morning is interesting, with a
large convective band with cloud tops below -70 C completing one
full cyclonic orbit around the hurricane. The NOAA Hurricane Hunters
earlier indicated that the central pressure had fallen from last
night, with the final reading at 965 mb. However, the 700 mb flight
level, SFMR, and tail Doppler radar winds have yet to respond to the
continued falling pressure. Therefore, the wind speed this advisory
will be held at 90 kt. Of note, the aircraft mission is reporting
that Earl has a fairly large closed eye , with an estimated
diameter of 50 n mi.

Based on the last few center fixes, Earl is starting to make the
turn to the north-northeast as it gradually accelerates, estimated
at 030/11 kt. A shortwave trough in the process of moving offshore
of the Eastern U.S. coastline and this feature, in combination with
mid-level ridging to the east of Earl, is expected to cause Earl to
bend further eastward as the flow accelerates. There have been very
few changes made to the NHC forecast track over the first 24-48
hours, with Earl expected to pass 75-100 n mi to the southeast of
Bermuda tonight into tomorrow morning. Shortly after 48 hours, Earl
will be captured by the digging shortwave trough with model guidance
indicating it will undergo a warm-seclusion-type extratropical
transition. This process will also likely result in a substantial
slow-down in the forward motion between 48-72 hours, and this
portion of the track forecast has the largest along-track spread,
related to the degree of phasing between Earl and this trough.
Thereafter, their combination should begin to move eastward into the
Atlantic Maritimes by the end of the forecast period, opting to
favor a blend between the GFS and ECMWF track solutions.

Per the latest SHIPS guidance, vertical wind shear over Earl is now
under 10 kt and is forecast to remain that way for the next 24 hours
as Earl traverses over 29 C sea-surface temperatures. Thus, steady
intensification is expected, with the assumption that the current
core structure of Earl fully consolidates and takes advantage of
this favorable environment. The peak intensity of 115 kt is still
under the latest LGEM and HCCA guidance. After 36 hours, Earl will
begin to undergo extratropical transition as the trough interaction
introduces substantial baroclinicity as vertical wind shear rapidly
increases. Earl is expected to transition into a powerful
hurricane-force extratropical low sometime between 48-60 hours, with
this low filling rather quickly thereafter, in good agreement with
the intensity consensus aids.

KEY MESSAGES:

1.  Although Earl's center is forecast to pass southeast of Bermuda,
tropical-storm-force winds are expected on the island this
afternoon through early Friday morning.  Hurricane-force winds are
possible on Bermuda this evening or tonight if Earl's track shifts
farther west than is currently forecast.

2.  Swells generated by Earl are building near Bermuda and are
expected to reach the U.S. East Coast later today and tonight.
These swells are likely to cause life-threatening surf and rip
current conditions through the weekend.  Please consult products
from your local weather office.


FORECAST POSITIONS AND MAX WINDS

INIT  08/1500Z 29.0N  65.0W   90 KT 105 MPH
 12H  09/0000Z 30.7N  64.2W  100 KT 115 MPH
 24H  09/1200Z 33.5N  61.7W  110 KT 125 MPH
 36H  10/0000Z 37.0N  57.7W  115 KT 130 MPH
 48H  10/1200Z 40.9N  53.5W  100 KT 115 MPH
 60H  11/0000Z 43.6N  49.9W   70 KT  80 MPH...POST-TROP/EXTRATROP
 72H  11/1200Z 44.9N  48.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  12/1200Z 46.1N  46.2W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  13/1200Z 47.1N  40.7W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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