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Subtropical Storm Alberto Forecast Discussion Number 7
2018-05-27 05:08:09| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat May 26 2018 000 WTNT41 KNHC 270307 CCA TCDAT1 Subtropical Storm Alberto Discussion Number 7...Corrected NWS National Hurricane Center Miami FL AL012018 1100 PM EDT Sat May 26 2018 Corrected typo in key message 3 During the past few hours, a burst of convection has formed just north of the low-level center of Alberto, which has caused the center to reform somewhat to the northeast of the previous position. Despite an overall increase in organization, however, reports from an Air Force Reserve Hurricane Hunter aircraft are at best ambiguous on whether the storm has strengthened. The maximum flight-level winds at 925 mb were 45 kt, which would support 30-35 kt at the surface. The maximum SFMR winds outside of the convective burst were 35-37 kt, but since these were higher than the associated flight-level winds it is unclear how reliable they were. In the convection, there were SFMR winds up to near 60 kt which may be due to downbursts and thus are unrepresentative of the strength of the storm. Finally, the central pressure has not fallen since the previous mission and is near 1001 mb. The initial intensity will remain 35 kt, but this could be conservative. In the next 24 h, Alberto should intensify as a subtropical storm due to the influence of a negative-tilt upper-level trough just west of the cyclone. After that time, the trough is forecast to become a cutoff upper-level low, with the center of Alberto near or just north of the low in an area of lighter shear. This evolution should allow the cyclone to develop a deeper warm core and become more symmetric, and this in turn should lead to Alberto transitioning from a subtropical to a tropical storm by 36-48 h. There is little intensity guidance that makes Alberto a hurricane before landfall, so the new intensity forecast keeps the same 55 kt peak and landfall intensities as the previous forecast. After landfall on the northern Gulf Coast, Alberto should steadily weaken over land through the remainder of the forecast period. For the next 12 h or so, Alberto should move generally northward, although some additional eastward reformation of the center remains possible. From 12-48 h, the cyclone should move north-northwestward as it merges with the upper-level low. This should be followed by a northward motion across the southeastern United States from 48-96 h and a subsequent recurvature into the westerlies. The forecast guidance is in good agreement, and the new forecast track is nudged just a little to the east of the previous track. On the current forecast track, Alberto would make landfall near the 48 h point. KEY MESSAGES: 1. Regardless of its exact track and intensity, Alberto is expected to produce heavy rainfall and flash flooding over western Cuba, southern Florida and the Florida Keys. Heavy rainfall and flooding potential will expand to include much of the central U.S. Gulf Coast region and portions of the southeastern United States beginning Sunday and will continue into next week. 2. Hazardous storm surge is possible along portions of the central and eastern Gulf Coast beginning on Sunday, including areas well east of the track of Alberto's center. Residents in the storm surge watch area are encouraged to follow any guidance given by their local government officials. 3. Tropical storm conditions are likely within the tropical storm warning area along the Florida west coast on Sunday and within the warning area along the northern Gulf Coast beginning Sunday night. 4. Dangerous surf and rip current conditions will likely spread northward along the eastern and northern Gulf Coast through Monday. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 23.9N 84.6W 35 KT 40 MPH 12H 27/1200Z 25.9N 84.6W 45 KT 50 MPH 24H 28/0000Z 27.7N 85.6W 50 KT 60 MPH 36H 28/1200Z 28.9N 86.4W 55 KT 65 MPH...TROPICAL STORM 48H 29/0000Z 30.4N 86.8W 55 KT 65 MPH...TROPICAL STORM 72H 30/0000Z 34.5N 87.6W 25 KT 30 MPH...INLAND 96H 31/0000Z 39.0N 86.5W 20 KT 25 MPH...INLAND 120H 01/0000Z 42.5N 82.0W 15 KT 15 MPH...POST-TROPICAL $$ Forecaster Beven
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