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Hurricane Larry Discussion Number  34
NWS National Hurricane Center Miami FL       AL122021
1100 PM AST Wed Sep 08 2021
 
The infrared satellite presentation of Larry this evening is giving 
the false impression of a well-organized hurricane, with a ring of 
colder cloud tops (-65 to -70 C) and a warm spot within. However, we 
are fortunate to have in-situ data provided by an Air Force 
Reconnaissance Hurricane Hunter mission investigating Larry this 
evening. Their observations show that Larry's center is actually 
southwest of the warm spot seen on satellite. In fact, the plane was 
unable to identify an eye with Larry, and the highest flight-level 
and SFMR winds were found nearly 80 nautical miles away from the 
center. Moreover, there remains a large discrepancy between the peak 
700-mb flight level winds (108-kt) versus the much lower SFMR peak 
values (67-kt). This suggests that the 90 percent reduction factor 
that is typically applied to 700-mb flight level winds in the 
eyewall may not be appropriate for this hurricane given its very 
large radius of maximum winds more associated with weaker outer 
convection. Given these factors, the latest NHC initial intensity 
has been lowered to 85 kt for this advisory. This intensity is also 
a good compromise between the SAB and TAFB subjective Dvorak 
estimates. 

The hurricane's heading is still off to the northwest with the 
latest motion at 330/14 kt. The track forecast philosophy has not 
changed much for the last few days, with Larry moving around the 
western periphery of a deep-layer subtropical anticyclone over the 
central Atlantic. The hurricane should make its closest approach to 
the east of Bermuda tomorrow as it gradually turns north-northwest 
and north. After that, the hurricane will begin to dramatically 
accelerate to the northeast as Larry is picked up by a deep-layer 
trough moving offshore of the eastern United States. The latest 
forecast track is quite similar to the previous one, and takes Larry 
across the southeast portion of Newfoundland in 48-60 hours. The 
official forecast remains close to the tightly clustered track 
guidance consensus. 

The current structure of Larry appears to be somewhat tilted with 
height, with the low-level center identified by recon located to the 
southwest of the apparent center on IR satellite. While the shear as 
diagnosed by SHIPS appears to be lower, it appears dry air has 
significantly disrupted Larry's inner core structure, to the point 
that it likely will be unable to take advantage of the more 
favorable conditions. The latest NHC intensity forecast is lower 
than the previous one, owing to the lower initial intensity, but 
begins to show more pronounced weakening after 24 hours when the 
hurricane will accelerate poleward of the northern wall of the Gulf 
Stream. However, Larry is still forecast to be a hurricane as it 
passes near or over Newfoundland, though likely beginning to 
undergo extratropical transition. The models continue to maintain 
Larry as a large formidable cyclone after extratropical transition 
is complete while it moves into the far north Atlantic east of 
Greenland. This cyclone will eventually merge with another 
extratropical cyclone by the end of the forecast period.
 
Key Messages:
 
1. Large swells generated by Larry will continue to affect the
Leeward Islands, portions of the Greater Antilles, the
Bahamas, Bermuda, and the east coast of the United States and
Atlantic Canada 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 expected there on Thursday, along with a risk of coastal
flooding.  A Tropical Storm Warning 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 undergoes transition
to a hurricane-force post-tropical cyclone. There is an increasing
risk of impacts from high winds, rainfall, and storm surge in
portions of Newfoundland, and interests there should monitor updates
to the forecast. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/0300Z 29.7N  60.3W   85 KT 100 MPH
 12H  09/1200Z 31.5N  61.5W   85 KT 100 MPH
 24H  10/0000Z 34.9N  62.3W   85 KT 100 MPH
 36H  10/1200Z 39.3N  60.8W   80 KT  90 MPH
 48H  11/0000Z 45.2N  55.8W   75 KT  85 MPH
 60H  11/1200Z 51.6N  48.2W   70 KT  80 MPH...POST-TROP/EXTRATROP
 72H  12/0000Z 57.4N  41.6W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  13/0000Z 63.8N  35.6W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  14/0000Z...DISSIPATED
 
$$
Forecaster Papin
 
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