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Hurricane Larry Forecast Discussion Number 30
2021-09-08 04:43:23| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 07 2021 000 WTNT42 KNHC 080243 TCDAT2 Hurricane Larry Discussion Number 30 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Tue Sep 07 2021 Larry's eye has become a little better defined since the previous advisory, and the eyewall convective cloud tops have cooled, with a nearly solid ring of -65C to -70C now surrounding the eye. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the central pressure has risen slightly to 966-968 mb and that peak 700-mb flight-level winds measured were 106 kt in the northeast quadrant. These data would suggest that the intensity has decreased a little to 95-96 kt. However, the peak flight-level wind of 106 kt was measured in the wake of a strong eyewall convective burst, suggesting that stronger winds could have been present in that convection. Also, if the surrounding eyewall convective ring closes off during the nocturnal convective maximum period in another six hours, then Dvorak intensity estimates would increase from the current T5.0/90 kt to T5.5/102 kt. Thus, Larry's intensity has been maintained at 100 kt for this advisory in order to avoid possible intensity vacillations. The initial motion estimate is 325/10 kt, based on reconnaissance aircraft fixes over the past 12 hours. There remains no significant change to the track forecast or reasoning over the past 48 hours. The latest NHC model guidance remains in strong agreement on Larry continuing to move northwestward and then northward around the western periphery of a deep-layer subtropical ridge during the next 48 hours or so. After passing east of Bermuda by early day 3, the hurricane is forecast to accelerate northeastward and move into the mid-latitude westerlies ahead of a large, eastward-moving trough that is currently approaching the northeastern United States and Atlantic Canada. By day 5, Larry is expected to move across the far north Atlantic. The new NHC track forecast is similar to the previous advisory track, and lies along the eastern edge of the tightly packed simple- and corrected-consensus track models. Larry's upper-level outflow pattern remains impressive, and has even expanded and accelerated on the east side owing to a southward-digging upper-level trough, which has enhanced the outflow in that part of the hurricane. The vertical wind shear affecting Larry is expected to remain low for the next 24 hours or so while the hurricane passes over even warmer sea-surface temperatures (SST) approaching 29.7 deg C, even though the oceanic heat content will be decreasing. However, entrainment of dry mid-level air along with eye fluctuations are expected to offset the warmer SSTs. Thus, a slow but steady decrease in intensity through 48-60 hours is expected. Late in the forecast period, colder waters and increasing southwesterly vertical wind shear exceeding 30 kt should induce a faster rate of weakening. By 96-120 hours, the global models also indicate Larry will be merging with a frontal zone. Therefore, the new intensity forecast continues to show extratropical transition during that time period. The official intensity forecast is similar to the previous advisory, and closely follows the simple- and corrected-consensus intensity models IVCN and NOAA-HCCA. Key Messages: 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. 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. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry's large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch 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 transitions to a hurricane-force post-tropical cyclone. There is a risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor the progress of Larry and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 25.8N 56.8W 100 KT 115 MPH 12H 08/1200Z 27.2N 58.0W 95 KT 110 MPH 24H 09/0000Z 29.2N 59.6W 95 KT 110 MPH 36H 09/1200Z 31.5N 61.3W 90 KT 105 MPH 48H 10/0000Z 34.6N 61.8W 90 KT 105 MPH 60H 10/1200Z 39.1N 60.1W 85 KT 100 MPH 72H 11/0000Z 44.5N 55.7W 80 KT 90 MPH 96H 12/0000Z 56.2N 43.6W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 13/0000Z 62.8N 33.6W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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