[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 080850
TCDAT2

Hurricane Larry Discussion Number  31
NWS National Hurricane Center Miami FL       AL122021
500 AM AST Wed Sep 08 2021

Larry's overall satellite presentation has not changed appreciably
overnight, however there has been some recent cooling of the cloud
tops in the surrounding ring of convection.  A fairly recent AMSR2
microwave overpass has revealed a fragmented inner eye with a band
or ring of convection at a fairly large radius from the center.
Subjective Dvorak Current Intensity (CI) numbers from TAFB and SAB
are T5.0 (90 kt) while objective UW/CIMSS ADT T-numbers are around
T5.8 (110 kt).  A consensus of these estimates, and the latest
SATCON estimate of 100 kt, is used as the initial intensity for this
advisory.  The next Air Force Reserve Hurricane Hunter aircraft is
scheduled to investigate Larry this morning and should provide in
situ data to help better ascertain the intensity and structure of
the hurricane.

Larry continues to move northwestward or 325/9 kt. The track
forecast reasoning is once again unchanged from before.  Larry is
expected to move northwestward and then northward around the
western portion of a deep-layer ridge during the next 36 to 48
hours, with the center of the hurricane passing east of Bermuda on
Thursday.  After that time, Larry should begin to accelerate
northeastward ahead of a deep-layer trough that will be moving
across the northeastern United States, and this will bring the
cyclone near or over southeastern Newfoundland in about 72 hours.
The track guidance continues to be in excellent agreement, and only
slight modifications were made to the previous official forecast.
The updated NHC track is near the various consensus aids and the
latest GFS ensemble mean.

The hurricane is forecast to remain within an area of low vertical
wind shear for the next day or two, but the upper-ocean heat
content will be gradually decreasing along the forecast path.
This, along with some upwelling beneath the relatively slow-moving
hurricane, is likely to result in gradual weakening over the next
couple of days.  After that time, increasing southwesterly shear and
much colder SSTs along the forecast track should result in
additional weakening.  The global models indicate that Larry will
merge with a frontal zone and complete its extratropical transition
in a little more than 3 days. The NHC intensity forecast is once
again similar to the previous advisory and is in best agreement
with the IVCN consensus aid.

Key Messages:

1. Large swells generated by Larry will continue to affect the
Leeward Islands, portions of the Greater Antilles, and the Bahamas
today.  Significant swells will begin to reach the east coast of
the United States and Atlantic Canada later today 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. The center of Larry is forecast to pass east of Bermuda on
Thursday, but given Larry's large size, tropical storm conditions
are possible there Thursday, along with a risk of heavy rainfall
and coastal flooding.  A Tropical Storm Watch is in effect for
Bermuda, and interests there should closely monitor the latest
forecast updates.

3. Larry is forecast to move near or over portions of southeastern
Newfoundland late Friday and Friday night as it transitions to a
hurricane-force post-tropical cyclone. There is a risk of impacts
from high winds, rainfall, and storm surge in portions of
Newfoundland, and interests there should monitor the progress of
Larry and updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  08/0900Z 26.5N  57.3W  100 KT 115 MPH
 12H  08/1800Z 28.0N  58.7W   95 KT 110 MPH
 24H  09/0600Z 30.1N  60.6W   95 KT 110 MPH
 36H  09/1800Z 32.9N  61.9W   90 KT 105 MPH
 48H  10/0600Z 36.7N  61.6W   85 KT 100 MPH
 60H  10/1800Z 41.7N  58.3W   80 KT  90 MPH
 72H  11/0600Z 47.3N  52.4W   75 KT  85 MPH
 96H  12/0600Z 58.8N  40.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  13/0600Z 65.0N  33.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Brown
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