[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 091500
TCDAT2

Hurricane Larry Discussion Number  36
NWS National Hurricane Center Miami FL       AL122021
1100 AM AST Thu Sep 09 2021

Larry continues to feature a banding-type eye on satellite images,
and the eye is clearly evident on the Bermuda radar.  Satellite and
radar data also show a moat-like area of low precipitation between
the eyewall and a large band of convection farther removed from the
center.  This outer band is expected to affect Bermuda or the
waters just east of the island over the next several hours.
Observations from an Air Force Hurricane Hunter aircraft indicate
that the central pressure has changed little since yesterday.
Flight-level winds from the aircraft were as high as 95 kt, but the
peak SFMR-observed surface winds were only 69 kt.  This again
indicates that in this case the strong winds aloft are not being
transported to the surface as effectively as in a typical hurricane
at lower latitudes.  Blending these data results in an intensity
estimate of 80 kt for this advisory.  This is just a little higher
than the latest subjective Dvorak estimates from TAFB and SAB.

The hurricane is gradually turning to the right and the initial
motion is 340/14 kt.  Larry is currently moving around the western
side of a deep-layer subtropical anticyclone over the central
Atlantic, and is passing east of Bermuda.  The flow on the east
side of a strong mid-level trough moving from the northeastern
United States to Atlantic Canada will cause Larry to turn toward
the northeast and accelerate in 24 to 48 hours.  Larry will move
near or over southeastern Newfoundland in 36 to 48 hours, and
then move over the far north Atlantic around the end of the
forecast period.  There is very little change to the NHC track
forecast from the previous advisory, which remains close to the
various consensus model solutions.

Larry is likely remain over warm waters with low shear for
another 24 hours or so.  Thus the system will probably maintain
much of its intensity into Friday.  By Friday night and over the
weekend, cooler SSTs and increasing shear should cause weakening.
However, baroclinic forcing associated with the trough to the west
of the hurricane could slow the weakening process.  The official
intensity forecast keeps Larry at hurricane-force through 48 hours
even as it undergoes extratropical transition.  In 3-4 days, the
global models show Larry merging with another large extratropical
cyclone over the north Atlantic.

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 later
today, and tropical storm conditions are expected there today,
along with a risk of coastal flooding.

3. 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 are storm surge are possible in portions of southeastern
Newfoundland where a hurricane watch is in effect. Interests there
should monitor updates to the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  09/1500Z 32.0N  61.6W   80 KT  90 MPH
 12H  10/0000Z 34.5N  62.2W   80 KT  90 MPH
 24H  10/1200Z 39.0N  60.8W   80 KT  90 MPH
 36H  11/0000Z 44.8N  56.1W   75 KT  85 MPH
 48H  11/1200Z 51.3N  49.1W   65 KT  75 MPH...POST-TROP/EXTRATROP
 60H  12/0000Z 57.0N  43.5W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  12/1200Z 61.0N  40.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  13/1200Z...MERGED

$$
Forecaster Pasch
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