[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 071453
TCDAT1

Hurricane Earl Discussion Number  19
NWS National Hurricane Center Miami FL       AL062022
1100 AM AST Wed Sep 07 2022

While it is evident that westerly vertical wind shear continues to
affect the overall satellite presentation of Earl, useful data
from the NOAA-P3 Hurricane Hunter aircraft indicates that the
hurricane is holding its own and has even strengthened a bit. Part
of this resilience could be due to the fact that the low and
mid-level centers of Earl are now vertically stacked with the wind
field relatively symmetric per the most recent set of Tail Doppler
Radar from the aircraft. However, the westerly shear is still
affecting the inner-core structure of the system, with its large 40
n mi wide eye open in the southern semicircle. The highest flight-
level winds from this morning's mission was 82 kt at 700 mb with
SFMR at 75 kt. The initial intensity was increased to 75 kt at the
8am intermediate advisory and remains this value for this advisory.

Fixes from this morning indicate that Earl has been moving just east
of due north, with the motion estimated at 005/6 kt. The hurricane
is caught in between a mid-level ridge now centered to its
southeast, with a positively-tilted upper-level trough located to
the northwest. This synoptic setup should enable Earl to begin
recurving north-northeastward and then northeastward as it
accelerates over the next 24-48 hours. The track guidance remains
tightly clustered during the early portion of the forecast, with the
GFS and ECMWF tracks now nearly identical during this period. The
official track forecast was only adjusted a touch east of the prior
one during this period. However, as noted previously, there is
increasing model support that the upper-level trough will ultimately
phase with Earl after 72 hours, resulting in the cyclone slowing
down significantly and potentially turning more northward in days
4-5. The official track forecast during this period now shows a bit
more of a northward bend and further slowdown compared to the prior
track, favoring a blend of the latest GFS and ECMWF forecast.

The persistent deep-layer westerly vertical wind shear that has been
impacting Earl the last several days is finally forecast to subside
later today, dropping below 10 kt in 24 hours. This decreasing
shear, in combination with very warm sea-surface temperatures,
favorable positioning in the right-entrance region of an upper-level
jet streak, and significant acceleration in the storm motion, is
likely to result in substantial strengthening of the surface wind
field and the latest NHC intensity forecast now shows a peak at 115
kt in 60-h, in good general agreement with the latest HCCA, yet
still under the LGEM intensity aid. After that, a significant
trough interaction is likely to rapidly increase baroclinicity, with
Earl forecast to become an extratropical-low as it phases with the
upper-level trough between days 3-4 in the forecast period.


KEY MESSAGES:

1.  Although Earl's center is forecast to pass southeast of Bermuda,
the wind field is expected to grow, with tropical-storm-force winds
forecast to spread across the island beginning Thursday afternoon
and continuing through Friday morning.

2.  Swells generated by Earl are expected to reach Bermuda by
tonight and the U.S. East Coast shortly thereafter.  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  07/1500Z 25.7N  65.7W   75 KT  85 MPH
 12H  08/0000Z 26.8N  65.6W   80 KT  90 MPH
 24H  08/1200Z 28.5N  65.2W   90 KT 105 MPH
 36H  09/0000Z 30.4N  64.1W  100 KT 115 MPH
 48H  09/1200Z 33.0N  61.5W  110 KT 125 MPH
 60H  10/0000Z 36.4N  57.3W  115 KT 130 MPH
 72H  10/1200Z 40.1N  53.1W  100 KT 115 MPH
 96H  11/1200Z 45.0N  49.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  12/1200Z 47.0N  47.9W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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