[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 062045
TCDAT2

Hurricane Larry Discussion Number  25
NWS National Hurricane Center Miami FL       AL122021
500 PM AST Mon Sep 06 2021

NOAA aircraft have been investigating Larry for much of this
afternoon, providing valuable information regarding the structure
and intensity of the hurricane. Peak 700-mb flight-level winds of
110 kt with SFMR winds of 101 kt were measured in the northwestern
eyewall a couple of hours ago, supporting an intensity of about 100
kt in that portion of the cyclone. During that pass through the
hurricane, the aircraft tail Doppler radar measured winds of 121 kt
at a height of 3 km in the northeastern eyewall, which equate to
about 109 kt at the surface. Therefore, the initial intensity has
been adjusted up to 110 kt for this advisory. A pair of dropsondes
into the eye of Larry measured a minimum central pressure of 956 mb.
Both the aircraft and earlier ASCAT data indicated that
hurricane-force winds extend up to 60 n mi from the center, while
tropical-storm-force winds extend up to 160 n mi from the center.

Larry is maintaining its stable, annular structure with a very
large, mostly clear eye. The environment surrounding Larry is not
forecast to change much over the next couple of days, so only some
minor fluctuations in intensity are anticipated during that time. By
72 hours, decreasing sea-surface temperatures and an increase in
vertical wind shear should cause the hurricane to begin weakening.
The only change to the NHC intensity forecast was a 5-kt increase
through the first few days to accommodate the adjustment required to
the initial intensity. By the end of the forecast period, Larry is
expected to transition to a powerful extratropical cyclone. The
latest NHC forecast remains on the high end of the guidance, closest
to the Decay-SHIPS model.

The hurricane continues to move northwest at 9 kt to the southwest
of a subtropical ridge. The forecast track confidence has remained
high over the past few days. Larry should continue its northwestward
motion through Wednesday, and then reach the western periphery of
the ridge in a few days, causing the cyclone to begin a turn to the
north, then northeast late this week. This track would bring Larry
on its closest approach to Bermuda on Thursday. After turning
northeast, the cyclone should accelerate into the mid-latitude
westerlies. The latest NHC forecast is little changed from the
previous one, and remains near the middle of tightly clustered track
guidance.


Key Messages:

1. Large swells generated by Larry are affecting the Lesser Antilles
and will spread to portions of the Greater Antilles, the Bahamas,
and Bermuda today through Tuesday.  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 few days as
a large and powerful hurricane, bringing a risk of strong winds,
heavy rainfall, and coastal flooding to the island by the middle of
this week.  While it is too soon to determine the magnitude of these
hazards and potential impacts on Bermuda, interests there should
closely monitor the latest forecast updates during the next several
days.


FORECAST POSITIONS AND MAX WINDS

INIT  06/2100Z 22.5N  53.9W  110 KT 125 MPH
 12H  07/0600Z 23.4N  55.0W  110 KT 125 MPH
 24H  07/1800Z 24.9N  56.3W  105 KT 120 MPH
 36H  08/0600Z 26.5N  57.6W  105 KT 120 MPH
 48H  08/1800Z 28.3N  59.1W  105 KT 120 MPH
 60H  09/0600Z 30.4N  60.7W  105 KT 120 MPH
 72H  09/1800Z 33.1N  61.7W  100 KT 115 MPH
 96H  10/1800Z 41.2N  57.9W   90 KT 105 MPH
120H  11/1800Z 51.7N  46.4W   70 KT  80 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto
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