[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 082059
TCDAT1

Hurricane Earl Discussion Number  24
NWS National Hurricane Center Miami FL       AL062022
500 PM AST Thu Sep 08 2022

Earl's intensification trend from last night took an unexpected halt
this morning, which was unusual given the reduction in vertical wind
shear. While an SSMIS pass at 1056 UTC showed a closed mid-level
eyewall, a more recent AMSR2 pass at 1717 UTC indicated that Earl
likely entrained some dry air that degraded the mid-level eyewall
structure, with a large cyclonic spiral opening to the west that
matched conventional satellite imagery at the time. The Air Force
Reserve Reconnaissance Aircraft has been sampling the hurricane this
afternoon, finding a minimum central pressure of 961 mb, but similar
to this morning, only found 700 mb flight level winds of 93 kt
(which reduces to 83 kt) and peak SFMR winds even lower at 64 kt.
Given these lastest in-situ observations, the initial intensity is
adjusted to 85 kt for this advisory. The aircraft observations, in
combination with ASCAT data, also indicate that Earl wind field is
growing larger, with 34-kt and 50-kt radii expanding in the
southeastern quadrant.

Earl is beginning to accelerate to the north-northeast, with
aircraft fixes indicating an estimated motion of 030/13 kt. Further
acceleration and a more northeastward turn is anticipated tonight
and tomorrow as Earl is caught up in the southwesterly flow between
a mid-level ridge to the east, and a digging mid-latitude trough to
the northwest. The guidance this cycle is very tightly clustered
upon the previous forecast track in over the next 24 hours, and very
few changes were made during this period for the latest NHC track.
On this path, Earl should make its closest approach about 75-100 n
mi southeast of Bermuda at around 0600 UTC. The same trough
mentioned above is then expected to capture Earl in 48-60 hours,
resulting in substantial slowdown in Earl's motion as the two
features phase together. This is the time period where the guidance
continues to exhibit a lot of along-track spread, related to the
degree of trough interaction, though the guidance this cycle has
shifted towards a stronger phasing solution, likely resulting in a
additional slowdown. The latest track forecast is not quite as slow
or far east as the latest GFS or ECMWF solutions, so further
adjustments may be needed if these trends continue.

Deep-layer (200-850 mb) vertical wind shear over Earl is now quite
low, under 10 knots per the GFS- and ECMWF-based SHIPS. However, the
structural degradation in Earl's inner core today has thrown a
monkey wrench in the anticipated intensification that was expected
to occur today. In fact, while the pressure has still been slowly
decreasing, it seems to have resulted in the wind field growing more
than strengthening the maximum sustained winds. While it is likely
that Earl will be able to mix out the earlier dry-air entrainment
near the core, it has shortened the window of favorable conditions
for intensification before the shear begins to rapidly increase
again in 36 hours. Thus, the intensity forecast has been reduced a
bit this cycle, now only showing a 105 kt peak in 24 hours, which is
now under the HCCA and LGEM guidance and closer to the ICVN
consensus aid. After 36 hours, increasing baroclinicity will lead to
a rapid increase in vertical wind shear, and extratropical
transition will likely be underway (likely a warm-seclusion-type
event), and be complete by 48 hours. The powerful extratropical low
is then forecast to weaken steadily, in 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 tonight into
tomorrow morning.  Hurricane-force winds are possible on Bermuda
tonight if Earl's track shifts farther west than currently
forecast.

2.  Swells generated by Earl are building near Bermuda and are
expected to reach the U.S. East Coast 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  08/2100Z 30.3N  64.4W   85 KT 100 MPH
 12H  09/0600Z 32.1N  62.9W   95 KT 110 MPH
 24H  09/1800Z 35.2N  59.6W  105 KT 120 MPH
 36H  10/0600Z 39.2N  55.0W  100 KT 115 MPH
 48H  10/1800Z 42.6N  51.8W   75 KT  85 MPH...POST-TROP/EXTRATROP
 60H  11/0600Z 44.0N  50.4W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  11/1800Z 45.0N  49.0W   45 KT  50 MPH...POST-TROP/EXTRATROP
 96H  12/1800Z 45.8N  47.0W   40 KT  45 MPH...POST-TROP/EXTRATROP
120H  13/1800Z 46.0N  41.4W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin
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