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Hurricane Sally Forecast Discussion Number 17
2020-09-15 16:46:01| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Tue Sep 15 2020 000 WTNT44 KNHC 151445 TCDAT4 Hurricane Sally Discussion Number 17 NWS National Hurricane Center Miami FL AL192020 1000 AM CDT Tue Sep 15 2020 The satellite presentation of Sally has not changed much since overnight. A ragged eye is seen in WSR-88D radar imagery, with a band occasionally trying to wrap around the southwestern side. A NOAA reconnaissance aircraft has just recently provided a new center fix, and data from the center drop indicated the minimum pressure is 983 mb. The first pass through the northeastern quadrant suggests that the 50-kt wind field may have expanded, but there has been little change in peak winds reported by the aircraft. The intensity has been held at 75 kt pending additional data from the NOAA P-3 mission that has just begun. A highly elevated oil rig just northeast of the center reported peak has reported sustained winds of 69 kt with a gust to 86 kt around 1200 UTC this morning. Sally has been meandering this morning, but the longer-term motion is northwestward or 315/2 kt. Sally remains within an area of weak steering flow, but a weak mid-level trough over the south-central United States is forecast to slide eastward over the next over the next couple of days. This pattern should cause Sally to move very slowly north-northwestward to northward over the next 24 hours, with the center of the hurricane nearing the northern Gulf Coast late tonight or Wednesday. By late Wednesday, Sally should turn northeastward as the aforementioned trough approaches Missouri and Arkansas. The new forecast has been nudged slightly eastward in the early portion of the track forecast, but the latter portion is very close to the previous advisory. The new track lies a little to the west of the various consensus aids in deference to the typically reliable GFS and ECMWF models that are near the left edge of the guidance envelope. Sally's forward motion is forecast to be around 5 kt or less throughout the forecast period, which will result in a long period of heavy rainfall and historic flooding along the north-central Gulf Coast. Moderate westerly shear and upwelling beneath the slow moving hurricane are likely to prevent strengthening today. The shear is forecast to increase tonight and although some slight weakening could occur before the center reaches the coast, Sally is predicted to remain a dangerous hurricane through landfall. Once Sally moves inland, rapid weakening is expected and circulation is forecast to lose definition and dissipate by day 4. Users are reminded to not focus on the specific timing and location of landfall. Life-threatening storm surge, historic flash flooding from heavy rainfall, and dangerous winds will affect a large portion of the north-central Gulf Coast during the next few days. KEY MESSAGES: 1. Life-threatening storm surge is expected from the Mouth of the Mississippi River to the Okaloosa/Walton County Line in the Florida Panhandle. The highest inundation is expected along the Alabama coast, including Mobile Bay. 2. Historic life-threatening flash flooding is likely through Wednesday along and just inland of the coast from the western Florida Panhandle to far southeastern Mississippi. Widespread moderate to major river flooding is forecast along and just inland of the central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding, are likely across inland portions of Mississippi, Alabama, northern Georgia, and the western Carolinas through the week. 3. Hurricane conditions are expected today within portions of the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 29.1N 88.2W 75 KT 85 MPH 12H 16/0000Z 29.6N 88.2W 75 KT 85 MPH 24H 16/1200Z 30.2N 88.1W 70 KT 80 MPH 36H 17/0000Z 31.0N 87.6W 55 KT 65 MPH...INLAND 48H 17/1200Z 31.9N 86.6W 35 KT 40 MPH...INLAND 60H 18/0000Z 32.6N 85.2W 25 KT 30 MPH...INLAND 72H 18/1200Z 33.0N 83.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1200Z...DISSIPATED $$ Forecaster Brown
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