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Hurricane Larry Forecast Discussion Number 19
2021-09-05 10:55:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 05 2021 000 WTNT42 KNHC 050855 TCDAT2 Hurricane Larry Discussion Number 19 NWS National Hurricane Center Miami FL AL122021 500 AM AST Sun Sep 05 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. FORECAST POSITIONS AND MAX WINDS 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 $$ Forecaster Reinhart
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