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Hurricane Sally Forecast Discussion Number 21
2020-09-16 10:58:22| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Wed Sep 16 2020 632 WTNT44 KNHC 160858 TCDAT4 Hurricane Sally Discussion Number 21 NWS National Hurricane Center Miami FL AL192020 400 AM CDT Wed Sep 16 2020 There has been little change in Sally's convective structure during the past few hours as seen in radar and satellite data. The initial intensity of 90 kt is based on previous reconnaissance SFMR surface wind data of 88 kt in the northeastern quadrant, along with average Doppler radar values of 114 kt between 4500-5000 ft ASL, which supports an equivalent surface wind speed of about 90 kt. The reconnaissance aircraft has recently measured peak 700-mb flight-level winds of 110 kt, but those winds may not be making it down to the surface based on earlier buoy wind reports underneath the eyewall. Although the northern eyewall has moved onshore between Mobile Bay and Pensacola Bay, some slight strengthening is still possible until the center of Sally's eye makes landfall later this morning. Rapid weakening is forecast after the center moves inland, and the system should become a remnant low in a couple of days. This is consistent with the latest model guidance. Radar and aircraft center fixes indicate that Sally's motion is north-northeastward, or 020/03 kt. No significant changes were required to the previous track forecast. The latest NHC model guidance continues to show Sally moving slowly north-northeastward this morning, and then turn northeastward with a gradual increase in forward speed by tonight. That motion should then continue for the next day or so. As Sally approaches the mid-latitude westerlies at higher latitudes, the tropical cyclone should turn toward the east-northeast with some slight increase in forward speed until it becomes a dissipating remnant low near the southeastern U.S. coast in 2-3 days. The official forecast is close to the latest corrected dynamical model consensus, HCCA, prediction. KEY MESSAGES: 1. Historic and catastrophic flooding is unfolding along and just inland of the coast from west of Tallahassee, Florida, to Mobile Bay, Alabama. In addition, widespread moderate to major river flooding is forecast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding, is likely across inland portions Alabama into central Georgia. Widespread flash and urban flooding is possible, as well as widespread minor to moderate river flooding, across western South Carolina into western and central North Carolina. Scattered flash and urban flooding is possible, as well as scattered minor river flooding in southeast Virginia. 2. Life-threatening storm surge is occurring along portions of the coastline from Alabama to the western Florida Panhandle, including Pensacola Bay and southern portions of Mobile Bay. 3. Hurricane conditions are expected this morning and then continue into this afternoon within portions of the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 30.1N 87.7W 90 KT 105 MPH 12H 16/1800Z 30.7N 87.2W 70 KT 80 MPH...INLAND 24H 17/0600Z 31.5N 86.3W 35 KT 40 MPH...INLAND 36H 17/1800Z 32.6N 84.7W 30 KT 35 MPH...INLAND 48H 18/0600Z 33.5N 82.4W 25 KT 30 MPH...INLAND 60H 18/1800Z 34.1N 79.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 19/0600Z...DISSIPATED $$ Forecaster Stewart
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