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| #1016724 (Received by flhurricane at: 4:47 PM 14.Sep.2020) TCDAT4 Hurricane Sally Discussion Number 14 NWS National Hurricane Center Miami FL AL192020 400 PM CDT Mon Sep 14 2020 After the rapid spin up of the inner core late this morning, the most recent aircraft passes through the center have not found any higher flight-level winds, however there have been a few SFMR winds of 85-90 kt reported. Using a blend of the flight-level and SFMR winds the initial intensity has been increased to 85 kt for this advisory. The next Air Force and NOAA aircraft have begun to sample the storm. Now that Sally has developed an inner core, the favorable atmospheric and ocean conditions of low vertical wind shear and warm water should allow for additional strengthening tonight while the system moves over the north-central Gulf of Mexico, and Sally could approach major hurricane strength. On Tuesday, the global models are predicting an increasing in southwesterly flow aloft, and this increase in shear, the potential for land interaction, and some upwelling over the shallower shelf waters over the northern Gulf should slow the intensification process. The NHC intensity forecast is again near the upper-end of the guidance envelope in best agreement with the HWRF and HFIP corrected consensus models. Sally did not move much earlier today as the center re-formation took place, but it appears that a slow west-northwestward to northwestward motion has resumed. Weak ridging over the southeastern United States is expected to steer Sally generally west-northwestward through early Tuesday. After that time, steering currents weaken and a slow northward motion is forecast as a weak mid-level trough develops over the the central United States. This trough is forecast to slide eastward, allowing Sally to begin a slow north-northeastward or northeastward motion. The specific timing and location of the turn will be critical as to the eventual location and timing of landfall along the north-central Gulf Coast. The UKMET and ECMWF models show a more northeastward motion after the turn and have trended eastward, with the ECMWF much slower than the remainder of the guidance. The NHC track has been adjusted eastward, and this requires and eastward extension of the hurricane warning. The new track most closely follows the GFS and it ensemble mean, but lies to the west of the various consensus aids, so some additional eastward adjustments could be needed in subsequent advisories. Given the uncertainty in the timing and location of the northward turn and the lack of well-defined steering currents, users are reminded to not focus on the exact forecast track or the specific timing and location of landfall. Hurricane-force winds, dangerous storm surge, and flooding rainfall will affect a large portion of the north-central Gulf Coast during the next few days. KEY MESSAGES: 1. It is too early to determine where Sally's center will move onshore given the uncertainty in the timing and location of Sally's northward turn near the central Gulf Coast. Users should not focus on the details of the official forecast track, since NHC's average forecast error at 36 to 48 hours is around 60 to 80 miles, and dangerous storm surge, rainfall, and wind hazards will extend well away from the center. 2. An extremely dangerous and life-threatening storm surge is expected for areas outside the southeastern Louisiana Hurricane and Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to the Okaloosa/Walton County Line in the Florida Panhandle, where a Storm Surge Warning is in effect. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are expected late tonight or early Tuesday within the Hurricane Warning area in southeastern Louisiana and are expected by late Tuesday and Tuesday night within the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. Tropical storm conditions are likely to begin this evening in these areas and preparations should be rushed to completion. 4. Life-threatening flash flooding is likely, as well as widespread minor to isolated major flooding, on area rivers along and just inland of the Central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding is likely across Mississippi and Alabama through the middle of the week. Flooding impacts are expected to spread farther across the Southeast through the week. Sally could continue to produce flash flooding across the Florida peninsula and prolong existing minor river flooding across west-central Florida through today. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 28.8N 87.4W 85 KT 100 MPH 12H 15/0600Z 29.2N 88.2W 95 KT 110 MPH 24H 15/1800Z 29.7N 88.7W 95 KT 110 MPH 36H 16/0600Z 30.4N 88.6W 90 KT 105 MPH...INLAND 48H 16/1800Z 31.3N 88.0W 55 KT 65 MPH...INLAND 60H 17/0600Z 32.2N 86.8W 30 KT 35 MPH...INLAND 72H 17/1800Z 32.9N 85.5W 25 KT 30 MPH...INLAND 96H 18/1800Z 33.5N 83.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/1800Z...DISSIPATED $$ Forecaster Brown |
