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Tropical Storm Sally Forecast Discussion Number 5
2020-09-12 22:56:54| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Sat Sep 12 2020 000 WTNT44 KNHC 122056 TCDAT4 Tropical Storm Sally Discussion Number 5 NWS National Hurricane Center Miami FL AL192020 500 PM EDT Sat Sep 12 2020 Sally continues to gradually become better organized, with developing convective banding features primarily over the southern portion of the circulation at this time. Upper-level outflow is still rather limited over the northern semicircle, possibly due to a weak upper low near the Georgia/Florida border. The latter feature is likely to soon move away from the area, however. Based on earlier scatterometer passes that showed tropical-storm-force winds over the Straits of Florida, the advisory intensity remains 35 kt. With very warm waters and a moist tropospheric environment ahead of Sally, strengthening seems likely. Some increase in westerly shear over the northern Gulf in 48-72 hours could at least slow down the intensification process around that time. The official intensity forecast is not far from the latest model consensus and a little above the previous forecast. Fixes from an Air Force Hurricane Hurricane aircraft, radar, satellite, and surface observations indicate a slow, generally westward motion of about 280/6 kt. A weakening mid-level high pressure system to the northeast of Sally should cause a generally west-northwestward to northwestward motion for the next few days. Because of the weakening steering currents, the cyclone should move rather slowly while it approaches the northern Gulf Coast. However, there is expected to be enough of a narrow north-south oriented ridge to the east of Sally in 3-4 days to steer the cyclone northward across the coast. The official track forecast has been nudged just slightly west of the previous one and lies between the simple and corrected dynamical track model consensus predictions. Users are reminded to not focus on the exact details of the track or intensity forecast as the average NHC track error at 96 h is around 150 miles and the average intensity error is around 15 mph. In addition, winds, storm surge, and rainfall hazards will extend far from the center. KEY MESSAGES: 1. Life threatening storm surge is possible along the Gulf Coast beginning on Monday, and a Storm Surge Watch is in effect for areas outside the southeast Louisiana Hurricane and Storm Damage Risk Reduction System from the Mouth of the Mississippi River to the Alabama/Florida border. Residents in these areas should follow any advice given by local officials. 2. Hurricane conditions are possible by early Tuesday from Grand Isle, Louisiana to the Alabama/Florida border, including Metropolitan New Orleans, with tropical storm conditions possible by Monday. 3. Sally is expected to produce flash flooding across portions of southern Florida and prolong existing minor river flooding across central Florida through Sunday. Flash, urban, and minor to moderate river flooding is likely across portions of the central Gulf Coast from Sunday through the middle of next week. 4. Tropical storm conditions are possible early next week in portions of the Florida Panhandle, where a Tropical Storm Watch is in effect. Wind gusts to tropical-storm force could occur over portions of the southern Florida Peninsula and the Florida Keys this evening. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 25.7N 81.9W 35 KT 40 MPH 12H 13/0600Z 26.4N 83.4W 40 KT 45 MPH 24H 13/1800Z 27.3N 85.3W 50 KT 60 MPH 36H 14/0600Z 28.0N 86.9W 60 KT 70 MPH 48H 14/1800Z 28.5N 88.1W 70 KT 80 MPH 60H 15/0600Z 29.0N 89.0W 75 KT 85 MPH 72H 15/1800Z 29.7N 89.3W 75 KT 85 MPH 96H 16/1800Z 31.1N 89.2W 55 KT 65 MPH...INLAND 120H 17/1800Z 33.1N 87.0W 30 KT 35 MPH...INLAND $$ Forecaster Pasch
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