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Hurricane Larry Discussion Number  18
NWS National Hurricane Center Miami FL       AL122021
1100 PM AST Sat Sep 04 2021
 
Larry has developed a large eye this evening that is 40-45 n mi in 
diameter, and the surrounding cloud tops have warmed somewhat.  
There have been no microwave passes over the hurricane for quite 
some time to assess its structure, but conventional satellite images 
suggest that Larry has taken on some annular characteristics (and 
the objective screening algorithm tagged it as marginally annular). 
Dvorak CI numbers and objective estimates are all between 100-102 
kt, so Larry's initial intensity is lowered slightly to 105 kt.  
 
Larry's motion remains west-northwestward (300 degrees) at 12 kt.  
The hurricane is expected to turn northwestward tonight or early 
Sunday around the southwestern periphery of a mid-level high 
centered over the central Atlantic, and then maintain that heading 
with some decrease in forward speed through day 4.  By day 5, Larry 
should turn northward and accelerate between the high and an 
approaching deep-layer trough over the eastern United States.  The 
updated NHC track forecast is largely unchanged from the previous 
advisory and is of high confidence since there is lower-than-normal 
spread among the track models.  Larry is forecast to make its 
closest approach to Bermuda in 4 to 5 days while it recurves around 
the ridge, but despite the high-confidence forecast, there is still 
uncertainty on how close that approach will be since several GEFS 
and ECMWF ensemble members bring Larry's center very close to or 
over the island.  Even with a track east of the island, Larry will 
be large enough to possibly cause some impacts on Bermuda.

Water vapor imagery shows some restriction to the outflow in the 
southwestern quadrant, which could be indicative of some shear.  
There continues to be some discrepancy among the models on how much 
shear the hurricane will contend with as it approaches a 
mid-/upper-level trough located north of the Leeward Islands.  The 
GFS keeps the shear over Larry fairly low since it's farther from 
the trough, while the ECMWF increases the shear to moderate or 
strong levels during the next 48 hours.  If Larry reaches the area 
of stronger shear, its intensity would obviously be adversely 
affected.  In terms of structure, significant re-intensification is 
now less likely since Larry has such a large eye and an expanding 
wind field.  On the positive side, the hurricane will be moving 
over gradually warmer waters for the next 3 days or so.  Given 
these conflicting factors, the updated NHC intensity forecast allows 
for some slight restrengthening in the short term but then keeps 
Larry's intensity steady for the next 3 days.  Many of the intensity 
models are even lower than what's shown in this forecast, so 
additional adjustments may be required in future advisories.    

 
Key Messages:
 
1. Large swells generated by Larry are expected to first reach the
Lesser Antilles on Sunday and will spread to portions of the Greater
Antilles, the Bahamas, and Bermuda Monday and Tuesday.  Significant
swells will likely reach the east coast of the United States and
Atlantic Canada around midweek.  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
advice of lifeguards and local officials through the upcoming week.
 
2. Larry is forecast to approach Bermuda during the next several
days, possibly as a major hurricane, bringing a risk of strong
winds, heavy rainfall, and coastal flooding to the island by the
middle of next week.  While it is too soon to determine the
magnitude of these hazards and potential impacts on Bermuda,
interests there should monitor changes to the forecast during the
next several days.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  05/0300Z 18.0N  48.0W  105 KT 120 MPH
 12H  05/1200Z 19.1N  49.5W  110 KT 125 MPH
 24H  06/0000Z 20.5N  51.3W  110 KT 125 MPH
 36H  06/1200Z 21.7N  53.0W  110 KT 125 MPH
 48H  07/0000Z 23.0N  54.5W  110 KT 125 MPH
 60H  07/1200Z 24.2N  56.0W  110 KT 125 MPH
 72H  08/0000Z 25.8N  57.5W  105 KT 120 MPH
 96H  09/0000Z 29.4N  60.5W  100 KT 115 MPH
120H  10/0000Z 35.1N  61.4W   90 KT 105 MPH
 
$$
Forecaster Berg
 
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