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Hurricane Larry Forecast Discussion Number 23
2021-09-06 10:52:55| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Sep 06 2021 000 WTNT42 KNHC 060852 TCDAT2 Hurricane Larry Discussion Number 23 NWS National Hurricane Center Miami FL AL122021 500 AM AST Mon Sep 06 2021 Recent microwave data indicate that Larry has likely completed an eyewall replacement cycle (ERC). The 0530 UTC AMSR2 imagery reveals that the hurricane now has a large, single eyewall structure with an eye diameter greater than 50 n mi, in contrast with the concentric eyewall structure noted yesterday. Larry's large eye appears somewhat ragged in conventional satellite imagery, as some convective debris clouds associated with the old eyewall continue to erode. Earlier scatterometer data confirmed that the 50- and 64-kt wind radii of Larry have broadened, likely as a result of the ERC. Based on a blend of the 102-kt Dvorak estimates from TAFB and SAB and a 107-kt ADT current intensity estimate, the initial intensity is set at 105 kt for this advisory. NOAA aircraft is scheduled to conduct a research mission into Larry later today, which should provide more information about Larry's structure and intensity. Larry is moving northwestward, or 305/10 kt. The track forecast for Larry remains of high confidence. The hurricane is expected to continue moving northwestward through midweek along the western periphery of a mid-level subtropical ridge over the central Atlantic. On Thursday, Larry is forecast to turn northward within the flow of an upper-level trough that is expected to move off the coast of the northeastern United States. By Friday, Larry should accelerate northeastward and recurve into the mid-latitudes, passing near or offshore Atlantic Canada. The latest track guidance is tightly clustered once again. Thus, the official NHC track forecast is virtually unchanged from the previous one and remains near the consensus aids HCCA and TVCA. Larry is forecast to pass east of Bermuda and make its closest approach to the island on Thursday. Given Larry's large size, some impacts could be felt even if the center remains well east of the island as forecast. The intensity forecast remains more complex. Now that the ERC is likely completed, some strengthening cannot be ruled out in the near-term if the large, consolidated eyewall is able to contract. However, the SHIPS guidance suggests some weak to moderate westerly shear is still present, and Larry's broad wind field could result in some upwelling of cooler waters that may inhibit intensification. Ultimately, these mixed signals suggest that some intensity fluctuations could occur over the next 24-36 h, and so the NHC intensity forecast shows little net change during this time. Thereafter, only gradual weakening is shown as the large hurricane will remain in a reasonably favorable environment of weak to moderate shear and warm SSTs through the 72-96 h period. By day 5, the cyclone will likely be in the process of extratropical transition, still as a powerful cyclone. Overall, the NHC intensity forecast lies on the higher end of the guidance, between the stronger statistical-dynamical models DSHP/LGEM and the weaker multi-model consensus aids IVCN/HCCA. Key Messages: 1. Large swells generated by Larry are affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda today through Tuesday. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores 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. Larry is forecast to approach Bermuda during the next few days as a large and powerful 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 06/0900Z 21.5N 52.4W 105 KT 120 MPH 12H 06/1800Z 22.6N 53.6W 110 KT 125 MPH 24H 07/0600Z 23.9N 54.9W 110 KT 125 MPH 36H 07/1800Z 25.3N 56.2W 105 KT 120 MPH 48H 08/0600Z 26.8N 57.5W 100 KT 115 MPH 60H 08/1800Z 28.5N 59.0W 100 KT 115 MPH 72H 09/0600Z 30.6N 60.6W 95 KT 110 MPH 96H 10/0600Z 36.7N 61.0W 90 KT 105 MPH 120H 11/0600Z 45.5N 52.0W 75 KT 85 MPH $$ Forecaster Reinhart
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