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Hurricane Larry Discussion Number  39
NWS National Hurricane Center Miami FL       AL122021
500 AM AST Fri Sep 10 2021
 
Larry's satellite presentation has remained largely unchanged
overnight. Deep convection continues to persist over and to the
northeast of the center, with a larger outer band around the
eastern portion of the circulation.  Subjective Dvorak intensity
estimates from TAFB and SAB have lowered slightly, and the initial
intensity has been adjusted downward to 75 kt.  This lies between
the lower subjective satellite estimates and the higher UW/CIMSS
ADT and SATCON values.  Larry is forecast to remain over warm
waters and in low vertical wind shear conditions this morning,
therefore little overall change in intensity is expected in the
short term.  The hurricane will cross the north wall of the Gulf
Stream over much cooler SSTs this afternoon, but the increasingly
fast forward speed of the system and baroclinic forcing from a
mid-latitude trough approaching from the west is likely to help
Larry maintain hurricane strength as is passes over southeastern
Newfoundland tonight.  Larry is forecast to become extratropical
shortly thereafter, and some slight weakening should occur before
the post-tropical cyclone is absorbed by a larger extratropical low
near southern Greenland in a couple of days.  The NHC intensity
forecast is similar to the HCCA and IVCN consensus aids and also
follows the trends of the latest global model guidance.
 
Larry has turned north-northeastward or 015/23 kt.  The track
guidance is once again in excellent agreement that Larry should
turn northeastward today and continue to accelerate ahead of
the aforementioned trough.  The center of Larry should pass over
southeastern Newfoundland tonight, but users are reminded to not
focus on the exact details of the track forecast as strong winds,
heavy rainfall, and a dangerous storm surge will extend far from
the center of the cyclone. The updated official forecast lies near 
the center of the track guidance envelope, but is slightly faster 
than the previous forecast during the first 36 hours.
 
Key Messages:
 
1. Larry is forecast to move over portions of southeastern
Newfoundland tonight as it undergoes transition to a
hurricane-force post-tropical cyclone.  Hurricane conditions, a
dangerous storm surge, and heavy rainfall are expected in portions
of southeastern Newfoundland where a Hurricane Warning in effect.
 
2. Large swells generated by Larry will continue to affect the
Bahamas, Bermuda, and the east coast of the United States and
Atlantic Canada through Saturday. These swells will 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.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  10/0900Z 37.7N  61.8W   75 KT  85 MPH
 12H  10/1800Z 41.9N  59.2W   75 KT  85 MPH
 24H  11/0600Z 48.6N  53.0W   70 KT  80 MPH
 36H  11/1800Z 55.0N  46.8W   60 KT  70 MPH...POST-TROP/EXTRATROP
 48H  12/0600Z 60.0N  42.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
 60H  12/1800Z...DISSIPATED
 
$$
Forecaster Brown
 
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