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Hurricane Larry Discussion Number  23
NWS National Hurricane Center Miami FL       AL122021
500 AM AST Mon Sep 06 2021
 
Recent microwave data indicate that Larry has likely completed an 
eyewall replacement cycle (ERC). The 0530 UTC AMSR2 imagery reveals 
that the hurricane now has a large, single eyewall structure with an 
eye diameter greater than 50 n mi, in contrast with the concentric 
eyewall structure noted yesterday. Larry's large eye appears 
somewhat ragged in conventional satellite imagery, as some 
convective debris clouds associated with the old eyewall continue to 
erode. Earlier scatterometer data confirmed that the 50- and 64-kt 
wind radii of Larry have broadened, likely as a result of the ERC. 
Based on a blend of the 102-kt Dvorak estimates from TAFB and SAB 
and a 107-kt ADT current intensity estimate, the initial intensity 
is set at 105 kt for this advisory. NOAA aircraft is scheduled to 
conduct a research mission into Larry later today, which should 
provide more information about Larry's structure and intensity.
 
Larry is moving northwestward, or 305/10 kt. The track forecast for 
Larry remains of high confidence. The hurricane is expected to 
continue moving northwestward through midweek along the western 
periphery of a mid-level subtropical ridge over the central 
Atlantic. On Thursday, Larry is forecast to turn northward within 
the flow of an upper-level trough that is expected to move off the 
coast of the northeastern United States. By Friday, Larry should 
accelerate northeastward and recurve into the mid-latitudes, passing 
near or offshore Atlantic Canada. The latest track guidance is 
tightly clustered once again. Thus, the official NHC track forecast 
is virtually unchanged from the previous one and remains near the 
consensus aids HCCA and TVCA. Larry is forecast to pass east of 
Bermuda and make its closest approach to the island on Thursday. 
Given Larry's large size, some impacts could be felt even if the 
center remains well east of the island as forecast.
 
The intensity forecast remains more complex. Now that the ERC is 
likely completed, some strengthening cannot be ruled out in the 
near-term if the large, consolidated eyewall is able to contract. 
However, the SHIPS guidance suggests some weak to moderate westerly 
shear is still present, and Larry's broad wind field could result in 
some upwelling of cooler waters that may inhibit intensification. 
Ultimately, these mixed signals suggest that some intensity 
fluctuations could occur over the next 24-36 h, and so the NHC 
intensity forecast shows little net change during this time. 
Thereafter, only gradual weakening is shown as the large hurricane 
will remain in a reasonably favorable environment of weak to 
moderate shear and warm SSTs through the 72-96 h period. By day 5, 
the cyclone will likely be in the process of extratropical 
transition, still as a powerful cyclone. Overall, the NHC intensity 
forecast lies on the higher end of the guidance, between the 
stronger statistical-dynamical models DSHP/LGEM and the weaker 
multi-model consensus aids IVCN/HCCA.
 
 
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  06/0900Z 21.5N  52.4W  105 KT 120 MPH
 12H  06/1800Z 22.6N  53.6W  110 KT 125 MPH
 24H  07/0600Z 23.9N  54.9W  110 KT 125 MPH
 36H  07/1800Z 25.3N  56.2W  105 KT 120 MPH
 48H  08/0600Z 26.8N  57.5W  100 KT 115 MPH
 60H  08/1800Z 28.5N  59.0W  100 KT 115 MPH
 72H  09/0600Z 30.6N  60.6W   95 KT 110 MPH
 96H  10/0600Z 36.7N  61.0W   90 KT 105 MPH
120H  11/0600Z 45.5N  52.0W   75 KT  85 MPH
 
$$
Forecaster Reinhart
 
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