[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 092059
TCDAT2

Hurricane Larry Discussion Number  37
NWS National Hurricane Center Miami FL       AL122021
500 PM AST Thu Sep 09 2021

A faint eye is still discernible on visible satellite images along
with some banding features.  On the Bermuda radar, the eyewall is
partially open over the southern semicircle of the hurricane.
Larry still has a prominent upper-tropospheric outflow pattern,
especially over the northern portion of the circulation.  The
advisory intensity is held at 80 kt, just above the latest
Dvorak Current Intensity Numbers from TAFB and SAB.

Larry is now heading a little west of north at an increasing forward
speed, and the initial motion is 345/17 kt.  The hurricane has been
moving around the western side of a large deep-layer high pressure
area centered over the central Atlantic.  By Friday, the system
should accelerate northeastward ahead of a strong mid-tropospheric
trough over the northeastern United States, and pass near or over
southeastern Newfoundland within 36 hours. Thereafter, post-tropical
cyclone Larry should move over the far North Atlantic.  The official
track forecast again lies close to the various consensus model
predictions.

The hurricane is expected to remain over warm waters with weak
vertical shear for another 12 to 24 hours.  Thereafter, Larry is
forecast to move over the cooler waters north of the Gulf Stream
and the shear will increase.  These factors should induce
weakening, but possible baroclinic forcing associated with the
trough to the west of the cyclone could result in Larry maintaining
some strength over the next few days.  The NHC intensity forecast
is similar to the latest NOAA corrected-consensus guidance, HCCA.
Global model predictions indicate that Larry will merge with a
front, and therefore become an extratropical cyclone, in 48 hours.
These models also show the system merging with another large
extratropical low over the north Atlantic in 3 to 4 days.


Key Messages:

1. Larry is forecast to move near or over portions of southeastern
Newfoundland Friday night or early Saturday morning as it undergoes
transition to a hurricane-force post-tropical cyclone.  Hurricane
conditions and dangerous storm surge are expected in portions of
southeastern Newfoundland where a Hurricane Warning in effect.

2. 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 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.

3. Tropical storm conditions are expected on Bermuda through
this evening, along with a risk of coastal flooding.


FORECAST POSITIONS AND MAX WINDS

INIT  09/2100Z 33.9N  62.2W   80 KT  90 MPH
 12H  10/0600Z 36.8N  61.8W   80 KT  90 MPH
 24H  10/1800Z 42.2N  59.0W   75 KT  85 MPH
 36H  11/0600Z 48.4N  52.9W   70 KT  80 MPH
 48H  11/1800Z 55.0N  46.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
 60H  12/0600Z 59.5N  42.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  12/1800Z 61.5N  40.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 96H  13/1800Z...MERGED

$$
Forecaster Pasch
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