Tropical Storm LARRY Advisory mar, 07-09

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Hurricane Larry Discussion Number  27
NWS National Hurricane Center Miami FL       AL122021
500 AM AST Tue Sep 07 2021

Larry has maintained a very warm, pronounced eye with a diameter of
around 45 to 50 n mi overnight. However, recent infrared satellite
imagery and earlier microwave data show some weaknesses in the
western eyewall of the hurricane, potentially signaling the
entrainment of some drier air into its inner core. This could be the
result of some moderate westerly shear impinging on the system. The
initial intensity is lowered to 105 kt for this advisory, based on a
0520 UTC SATCON estimate of 103 kt and T5.5/102 kt current intensity
Dvorak estimates from TAFB and SAB. An Air Force Reserve hurricane
hunter reconnaissance flight is scheduled to investigate Larry later
this morning, which should provide more insight into the hurricane's
structure and intensity.

Larry is moving toward the northwest at 315/9 kt, as the hurricane
is being steered around a subtropical ridge over the central
Atlantic. This general motion is expected to continue for the next
48 h or so. By Thursday, the hurricane is forecast to turn northward
within the flow between the ridge and an approaching deep-layer
trough that will be crossing the northeastern United States. As the
trough moves over the western Atlantic, Larry should accelerate
northeastward deeper into the mid-latitudes on Friday and Saturday,
passing near or over portions of Atlantic Canada. The latest NHC
track forecast lies near the HCCA and TVCA consensus aids, and no
significant adjustments were made from the previous forecast. Larry
is expected to pass east of Bermuda on Thursday as a large
hurricane. Given the expansive size of its wind field, a Tropical
Storm Watch could be required for the island later today.

Although the warm sea-surface temperatures and diminishing vertical
wind shear along Larry's forecast track appear favorable during the
next couple of days, it may not be able to take advantage of these
conditions due to its large size, as well as the potential for
another eyewall replacement cycle. As previously noted, Larry's
broad wind field and moderate forward speed could also result in
some upwelling of cooler waters near its inner core. There remains a
split in the intensity guidance, with the statistical-dynamical
guidance notably higher than the coupled atmosphere-ocean models.
The official NHC intensity forecast shows a gradual weakening of
Larry during the next several days. Nonetheless, Larry will remain a
forceful hurricane that continues to produce significant swell with
far-reaching impacts through the week. After 72 h, Larry should
begin its extratropical transition, and the official forecast shows
Larry becoming a hurricane-force extratropical cyclone by 96 h.


Key Messages:

1. Large swells generated by Larry will continue to affect the
Lesser Antilles, portions of the Greater Antilles, and the Bahamas
through midweek.  Significant swells should reach the east coast of
the United States and Atlantic Canada by midweek and continue
affecting these shores through the end of the week.  These swells
will likely cause life-threatening surf and rip current conditions,
and beachgoers and other interests along these coasts are urged to
follow the guidance of lifeguards and local officials this week.

2. Larry is forecast to approach Bermuda during the next couple of
days as a large and powerful hurricane, bringing a risk of strong
winds, heavy rainfall, and coastal flooding to the island by
Thursday.  Tropical storm watches could be needed for the island
later today, and interests in Bermuda should closely monitor the
latest forecast updates.


FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 23.8N  55.1W  105 KT 120 MPH
 12H  07/1800Z 24.9N  56.0W  100 KT 115 MPH
 24H  08/0600Z 26.5N  57.4W   95 KT 110 MPH
 36H  08/1800Z 28.4N  59.1W   95 KT 110 MPH
 48H  09/0600Z 30.6N  60.8W   95 KT 110 MPH
 60H  09/1800Z 33.3N  61.8W   90 KT 105 MPH
 72H  10/0600Z 37.1N  61.0W   85 KT 100 MPH
 96H  11/0600Z 47.7N  52.4W   75 KT  85 MPH...POST-TROP/EXTRATROP
120H  12/0600Z 57.0N  43.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Reinhart