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HURRICANE CENTER: Larry Turns, Heavy Rains May Again Hit Louisiana, Gulf

Gulf system hurricane centere
Outlook from National Hurricane Center for September 5, 2021.


BOCA RATON, FL ( (Copyright © 2021 MetroDesk Media, LLC) — Major Hurricane Larry is now turning towards the north, reducing the fear of a direct hit on the United State mainland.

But while Larry is less of an issue, a new system is worrisome for already deluged residents of the Gulf Coast, where the Ida cleanup continues. While the system — in yellow, above — may not form into a named storm, there is a growing chance of extremely poor weather ahead.

First, the Larry update from the National Hurricane Center:

Hurricane Larry update for early Sunday morning, September 5, 2021.
Larry remains a powerful hurricane this morning. The system has a 
warm, well-defined eye with a large diameter of around 40 n mi. 
Larry's central dense overcast has become more symmetric overnight, 
although the upper-level outflow is still somewhat restricted on the 
southwestern side of the hurricane. This is likely an indication of 
some vertical wind shear impinging on the cyclone. However, recent 
AMSR2 microwave data indicate that the vortex is still well-aligned 
vertically, with a pronounced eyewall that slopes outward with 
height. The initial intensity is held at 105 kt for this advisory 
based on consensus T5.5/102 kt Dvorak classifications from TAFB and 
SAB, and a recent UW-CIMSS ADT estimate of 105 kt. 

The initial motion of Larry is northwestward, or 305/12 kt. Larry is 
expected to continue moving northwestward for the next several days 
around the southwestern periphery of a mid-level ridge over the 
central Atlantic. By Thursday, the cyclone is forecast to accelerate 
northward ahead of a deep-layer trough that will move off the east 
coast of the United States later this week. The latest track 
guidance is very tightly clustered, and the official NHC forecast is 
similar to the previous one and lies near the multi-model consensus 
aids. Confidence remains high in Larry's track forecast given the 
excellent model agreement. The hurricane is still expected to make 
its closest approach to Bermuda at days 4 and 5, but it remains too 
early to pinpoint how close it will come to the island. Even if the 
center passes east of Bermuda as forecast, it could still be large 
enough to produce some impacts on the island.

Over the next few days, some fluctuations in Larry's intensity are 
possible. The oceanic heat content along the forecast track is 
certainly sufficient for some intensification. However, vertical 
wind shear associated with an upper-level trough/low to the west of 
Larry may inhibit strengthening at times during the next couple of 
days, especially if the stronger shear values in the ECMWF-based 
SHIPS guidance are realized. Given Larry's large eye size, it does 
not appear as if the cyclone is poised to significantly intensify. 
The official NHC intensity forecast shows slight strengthening in 
the near-term, but then levels off the intensity through 48 h. The 
NHC forecast keeps Larry at major hurricane intensity through day 4, 
as the environment appears favorable enough between 48-96 h for 
Larry to maintain its organization, even as the cyclone gains 
latitude. Overall, this forecast lies on the high end of the 
intensity guidance, above the HFIP corrected consensus approach 
(HCCA) and the other multi-model consensus aids.

Key Messages:

1. Large swells generated by Larry are expected to reach the Lesser 
Antilles today and will spread to portions of the Greater Antilles, 
the Bahamas, and Bermuda on Monday and Tuesday.  Significant swells 
will likely reach the east coast of the United States and Atlantic 
Canada by 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 this 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 this week.  While it is too soon to determine the 
magnitude of these hazards and potential impacts on Bermuda, 
interests there should closely monitor the latest forecast updates 
during the next several days.


INIT  05/0900Z 18.8N  49.0W  105 KT 120 MPH
 12H  05/1800Z 19.9N  50.4W  110 KT 125 MPH
 24H  06/0600Z 21.2N  52.1W  110 KT 125 MPH
 36H  06/1800Z 22.4N  53.6W  110 KT 125 MPH
 48H  07/0600Z 23.6N  55.0W  110 KT 125 MPH
 60H  07/1800Z 25.0N  56.4W  105 KT 120 MPH
 72H  08/0600Z 26.5N  57.8W  105 KT 120 MPH
 96H  09/0600Z 30.4N  60.8W  100 KT 115 MPH
120H  10/0600Z 36.5N  61.0W   90 KT 105 MPH

This is the update for growing system in the Gulf.

There is no concern, for now, of it developing into a hurricane, but the area marked in yellow, above, indicates where a system could form.

The yellow oval is not necessarily a direction of travel.

1. Disorganized showers and thunderstorms over portions of Central 
America and the Yucatan Peninsula are associated with a surface 
trough and an upper-level disturbance.  Locally heavy rains are 
likely to continue today over that area.  The system is forecast to 
move northwestward over the southwestern Gulf of Mexico later today, 
then move slowly northward or northeastward over the western or 
central Gulf of Mexico.  Upper-level winds are only expected to be 
marginally conducive for tropical cyclone formation, but some slow 
development is possible while the system moves across the Gulf of 
Mexico through the middle of the week. 
* Formation chance through 48 hours...low...near 0 percent. 
* Formation chance through 5 days...low...30 percent.

Forecaster Pasch



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