Hurricane LARRY (Text)

Hurricane Larry Discussion Number  17
NWS National Hurricane Center Miami FL       AL122021
500 PM AST Sat Sep 04 2021
Larry remains a formidable hurricane this afternoon. Both visible 
and infrared satellite bands show the hurricane has a well-defined 
and warm eye (greater than 10 C) surrounded by a cold ring of 
eyewall convection (-60 to -70 C). An AMSR2 microwave pass received 
at 1630 UTC showed the well-defined eye of Larry, though the 89 GHz 
channel hinted that the eyewall was weaker on its eastern side. 
Taking a look at the high-density atmospheric motion vectors (AMVs), 
available thanks to a GOES-16 1-minute updating domain over Larry, 
there is some restriction of Larry's outflow to the southwest. 
Flight-level wind data from the NASA-DC8 aircraft conducting a 
research mission around Larry also showed some light southwesterly 
flow between 10-20 kt just a few degrees to the south and west of 
the storm center. These data suggest that the upper-level wind 
environment is not as pristine as earlier suggested by SHIPS 
guidance, with the southwesterly flow likely restricting Larry's 
outflow in that quadrant. The SAB/TAFB subjective Dvorak intensity 
estimates are unchanged from this morning, and the latest UW-CIMSS 
ADT and SATCON estimates have also plateaued in the 105-110 kt 
range. Therefore, Larry was maintained as a 110 kt hurricane this 
Larry remains on a west-northwest track this afternoon, but a bit 
slower at 300/12 kt. There has been little change to the track 
philosophy over the next several days, as the guidance is in good 
agreement that Larry will maintain a continued west-northwest 
heading while gradually slowing down as it rounds the southern 
periphery of a large mid-level ridge. However, there has been a 
notable eastward shift in the track guidance in the short-term. The 
latest ECMWF run, which had previously been on the southwest side of 
the track guidance envelope, is now very similar or even a tad east 
of the latest GFS run. This shift has also resulted in an eastward 
adjustment in the consensus aids this afternoon. The latest NHC 
track forecast was adjusted a bit to the right early on, but not as 
far right as the HCCA and TVCA aids. After 72 hours, the track 
guidance actually converges very close to the previous track 
forecast, and few changes were needed after this time period. Based 
on this forecast, Larry will continue moving across the central 
Atlantic in the coming days, and be approaching Bermuda from the 
southeast in the day 4 to 5 forecast period.
The existence of some light upper-level southwesterly flow ahead of 
Larry today was bit of a surprise, since the SHIPS guidance from the 
last few days suggested the shear-vector would be out of the east 
and weak. Indeed, the latest ECMWF-SHIPS guidance now shows moderate 
southwesterly vertical wind shear beginning earlier, and peaking 
between 20-25 knots in 36 to 48 hours. While the GFS-SHIPS shear 
remains much lower, given what I'm seeing from the latest 
upper-level flow in front of Larry, the ECMWF seems closer to 
correct. For this reason, the latest NHC intensity guidance now 
shows a bit of weakening after 24 hours, when the shear magnitude is 
expected to peak as the hurricane interacts with a large tropical 
upper-tropospheric trough (TUTT) located to its northwest. However, 
Larry has a large and vertically-deep circulation, and ultimately it 
will win the battle against the more vertically shallow TUTT, which 
is forecast to cut off and move away from the hurricane's expansive 
upper-level outflow. By 60 hours, this change in the synoptic 
pattern should once again reduce the vertical wind shear over Larry, 
and it will have a chance to achieve a secondary peak between the 
60-84 hour time-frame. However, eyewall replacement cycles could 
also occur at any time over the next 2-5 days, providing additional 
intensity fluctuations that make this a challenging intensity 
forecast. The latest NHC intensity forecast is lower than the 
previous one, but still remains higher than the latest HCCA 
consensus aid. Regardless of the details, Larry is expected to 
remain a large major hurricane over the next 3-4 days.
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.
INIT  04/2100Z 17.4N  47.1W  110 KT 125 MPH
 12H  05/0600Z 18.4N  48.6W  115 KT 130 MPH
 24H  05/1800Z 19.8N  50.6W  120 KT 140 MPH
 36H  06/0600Z 21.0N  52.3W  115 KT 130 MPH
 48H  06/1800Z 22.2N  54.0W  110 KT 125 MPH
 60H  07/0600Z 23.4N  55.6W  110 KT 125 MPH
 72H  07/1800Z 24.7N  57.0W  115 KT 130 MPH
 96H  08/1800Z 28.3N  59.9W  110 KT 125 MPH
120H  09/1800Z 33.4N  61.9W   95 KT 110 MPH
Forecaster Papin

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Page last modified: Friday, 31-Dec-2021 12:09:27 UTC