[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 072100
TCDAT1

Hurricane Earl Discussion Number  20
NWS National Hurricane Center Miami FL       AL062022
500 PM AST Wed Sep 07 2022

The structure of Earl is gradually improving, with deep convective
cold tops rotating around the core with an occasional warm spot
becoming evident on both infrared and visible satellite imagery. An
Air Force Reserve Hurricane Hunter mission has been flying through
Earl this afternoon, and they found a peak 700 mb flight level wind
of 90 kt in the SE quadrant of the hurricane. However, SFMR winds
have been lower than earlier observed in the NOAA P-3 mission and
the central pressure has stabilized somewhere in the 974-976 mb
range. These observations support keeping the intensity at 75 kt for
this advisory, which is also in agreement with the 1800 UTC Dvorak
T-numbers from both TAFB and SAB.

Center fixes from the aircraft show that Earl continues to move east
of due north estimated at 010/7 kt, and may be in the initial stages
of making a more rightward turn. The track reasoning has not changed
for the next couple of days, where Earl is expected to gradually
turn to the northeast and accelerate as it is caught in between a
mid-level ridge to the southeast, and a digging mid-latitude trough
to the northwest. The aforementioned trough is forecast to
ultimately capture Earl sometime in the 60-96 hour period, though
timing differences between the guidance are driving significant
along track spread in the forecast by that time. The latest NHC
track forecast was largely unchanged in the short-term, remaining
close to the tightly clustered guidance, though was shifted a bit
east compared to the prior cycle after Earl becomes extra-tropical.

The deep-layer vertical wind shear is beginning to decrease over
Earl, now under 20-kt in both GFS- and ECMWF-based SHIPS guidance.
This shear is forecast to decrease further tonight and be 10 kt or
under from 24-48 hours. Sea-surface temperatures are also expected
to remain at 29 C or warmer over this same time span. In terms of
the high-resolution regional hurricane model guidance, the most
recent HMON, experimental HAFS-S and HAFS-A, and COAMPS-TC all
explicitly show Earl becoming a Category 4 hurricane over the next
48-60h. The COAMPS-TC ensemble from the 00z cycle also indicated at
least 75 percent of its members becoming a Category 4 hurricane as
the hurricane passes by to the southeast of Bermuda. Finally, DTOPS
RI-probabilities from the latest SHIPS run indicate a greater than
50 percent chance of a 35 kt increase in intensity over the next 24
hours. While the latest intensity forecast will not go quite that
high, it does show a 40 kt increase in intensity in 48 hours still
making Earl a Category 4 hurricane. While it is relatively rare to
see such an intense hurricane at that latitude in the forecast
period, the guidance support, plus the favorable environment of Earl
being positioned in the right entrance region of a upper-level jet
streak ahead of the trough should provide both good dynamical
support on top of the favorable thermodynamic environment by the
warm SSTs. After 60 h, Earl will likely rapidly undergo
extra-tropical transition as an upper-level trough digs in and
captures Earl, increasing baroclinicity and removing the deep
convection as the storm moves poleward of the Gulf Stream.


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. The Bermuda Weather Service
has also issued a Hurricane Watch for the island.

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  07/2100Z 26.5N  65.5W   75 KT  85 MPH
 12H  08/0600Z 27.8N  65.2W   85 KT 100 MPH
 24H  08/1800Z 29.7N  64.5W   95 KT 110 MPH
 36H  09/0600Z 32.0N  62.7W  105 KT 120 MPH
 48H  09/1800Z 35.0N  59.4W  115 KT 130 MPH
 60H  10/0600Z 38.6N  55.0W  110 KT 125 MPH
 72H  10/1800Z 41.8N  50.6W   80 KT  90 MPH...POST-TROP/EXTRATROP
 96H  11/1800Z 45.0N  46.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  12/1800Z 47.0N  41.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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