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Hurricane Larry Forecast Discussion Number 34
2021-09-09 04:58:23| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 08 2021 000 WTNT42 KNHC 090258 TCDAT2 Hurricane Larry Discussion Number 34 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Wed Sep 08 2021 The infrared satellite presentation of Larry this evening is giving the false impression of a well-organized hurricane, with a ring of colder cloud tops (-65 to -70 C) and a warm spot within. However, we are fortunate to have in-situ data provided by an Air Force Reconnaissance Hurricane Hunter mission investigating Larry this evening. Their observations show that Larry's center is actually southwest of the warm spot seen on satellite. In fact, the plane was unable to identify an eye with Larry, and the highest flight-level and SFMR winds were found nearly 80 nautical miles away from the center. Moreover, there remains a large discrepancy between the peak 700-mb flight level winds (108-kt) versus the much lower SFMR peak values (67-kt). This suggests that the 90 percent reduction factor that is typically applied to 700-mb flight level winds in the eyewall may not be appropriate for this hurricane given its very large radius of maximum winds more associated with weaker outer convection. Given these factors, the latest NHC initial intensity has been lowered to 85 kt for this advisory. This intensity is also a good compromise between the SAB and TAFB subjective Dvorak estimates. The hurricane's heading is still off to the northwest with the latest motion at 330/14 kt. The track forecast philosophy has not changed much for the last few days, with Larry moving around the western periphery of a deep-layer subtropical anticyclone over the central Atlantic. The hurricane should make its closest approach to the east of Bermuda tomorrow as it gradually turns north-northwest and north. After that, the hurricane will begin to dramatically accelerate to the northeast as Larry is picked up by a deep-layer trough moving offshore of the eastern United States. The latest forecast track is quite similar to the previous one, and takes Larry across the southeast portion of Newfoundland in 48-60 hours. The official forecast remains close to the tightly clustered track guidance consensus. The current structure of Larry appears to be somewhat tilted with height, with the low-level center identified by recon located to the southwest of the apparent center on IR satellite. While the shear as diagnosed by SHIPS appears to be lower, it appears dry air has significantly disrupted Larry's inner core structure, to the point that it likely will be unable to take advantage of the more favorable conditions. The latest NHC intensity forecast is lower than the previous one, owing to the lower initial intensity, but begins to show more pronounced weakening after 24 hours when the hurricane will accelerate poleward of the northern wall of the Gulf Stream. However, Larry is still forecast to be a hurricane as it passes near or over Newfoundland, though likely beginning to undergo extratropical transition. The models continue to maintain Larry as a large formidable cyclone after extratropical transition is complete while it moves into the far north Atlantic east of Greenland. This cyclone will eventually merge with another extratropical cyclone by the end of the forecast period. Key Messages: 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada 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. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry's large size, tropical storm conditions are expected there on Thursday, along with a risk of coastal flooding. A Tropical Storm Warning is in effect for Bermuda, and interests there should closely monitor the latest forecast updates. 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it undergoes transition to a hurricane-force post-tropical cyclone. There is an increasing risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 29.7N 60.3W 85 KT 100 MPH 12H 09/1200Z 31.5N 61.5W 85 KT 100 MPH 24H 10/0000Z 34.9N 62.3W 85 KT 100 MPH 36H 10/1200Z 39.3N 60.8W 80 KT 90 MPH 48H 11/0000Z 45.2N 55.8W 75 KT 85 MPH 60H 11/1200Z 51.6N 48.2W 70 KT 80 MPH...POST-TROP/EXTRATROP 72H 12/0000Z 57.4N 41.6W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 13/0000Z 63.8N 35.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0000Z...DISSIPATED $$ Forecaster Papin
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