| Track: https://www.nhc.noaa.gov/refresh/graphics_at4+shtml/?cone#contents Hurricane Sally Discussion Number 18 NWS National Hurricane Center Miami FL AL192020 400 PM CDT Tue Sep 15 2020 Sally has been inching its way toward the north-central Gulf Coast today. The overall structure of the storm has remained about the same during the day with a large ragged eye in apparent in radar imagery. A NOAA P-3 aircraft that has been sampling the storm since late this morning has reported peak flight-level winds of 76 kt, and NWS Doppler radar has shown velocities of 75-80 kt at around 7000 ft. The intensity was reduced to 70 kt on the 1800 UTC intermediate advisory and remains at that value for this advisory. Radar and aircraft fixes show that Sally has been moving very slowly toward the north or 350/2 kt. The track forecast philosophy remains unchanged from the previous advisory. Sally is currently located within an area of weak steering flow between a couple of mid-level ridges to its east and west. A weak mid-level trough over the south-central United States is forecast to slide eastward over the next few days, which should cause Sally to turn north-northeastward and then northeastward over the next 24-36 hours. Sally's forward speed is expected to remain quite slow over the next 24-48 hours, but the guidance has trended slightly faster after that time. The slow forward speed is likely to result in a historical rainfall event for the north-central Gulf Coast. It may sound like a broken record, but the track guidance has again shifted eastward during the first 24-36 hours, and the NHC forecast has been adjusted accordingly. Since Sally has a large wind field, and storm surge and rainfall hazards extend far from the eye, users should not focus on the exact forecast track or specific location and timing of landfall as strong winds and bands of heavy rainfall are already affecting the Gulf Coast and will continue to do so for quite some time. The combination of upwelling and moderate westerly shear is likely to result in little change in strength prior to Sally moving onshore. Once the center of the hurricane moves onshore, rapid weakening is expected and the global models indicate that the circulation will becoming elongated along a frontal boundary in 3 to 4 days. KEY MESSAGES: 1. Historic life-threatening flash flooding due to rainfall is likely through Wednesday along and just inland of the coast from the Florida Panhandle west of the Apalachicola River 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, is likely across inland portions of Mississippi and Alabama, and into Georgia and the western Carolinas this week. 2. Life-threatening storm surge is expected along portions of the coastline from Alabama to the western Florida Panhandle, including Mobile Bay. 3. Hurricane conditions are expected this evening and overnight within portions of the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 29.5N 88.1W 70 KT 80 MPH 12H 16/0600Z 29.9N 88.1W 70 KT 80 MPH 24H 16/1800Z 30.6N 87.7W 60 KT 70 MPH...INLAND 36H 17/0600Z 31.5N 86.9W 40 KT 45 MPH...INLAND 48H 17/1800Z 32.5N 85.3W 30 KT 35 MPH...INLAND 60H 18/0600Z 33.1N 83.3W 25 KT 30 MPH...INLAND 72H 18/1800Z 33.5N 81.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1800Z...DISSIPATED $$ Forecaster Brown Hurricane Sally Advisory Number 18 NWS National Hurricane Center Miami FL AL192020 400 PM CDT Tue Sep 15 2020 ...TROPICAL-STORM-FORCE WINDS SPREADING ONSHORE ALONG THE NORTH-CENTRAL GULF COAST... ...HISTORIC LIFE-THREATENING FLOODING LIKELY ALONG PORTIONS OF THE NORTHERN GULF COAST... SUMMARY OF 400 PM CDT...2100 UTC...INFORMATION ---------------------------------------------- LOCATION...29.5N 88.1W ABOUT 85 MI...135 KM S OF MOBILE ALABAMA ABOUT 90 MI...140 KM SW OF PENSACOLA FLORIDA MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H PRESENT MOVEMENT...N OR 350 DEGREES AT 2 MPH...4 KM/H MINIMUM CENTRAL PRESSURE...979 MB...28.91 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for... * Mouth of the Mississippi River to the Okaloosa/Walton County Line Florida * Mobile Bay A Hurricane Warning is in effect for... * East of Bay St. Louis to Navarre Florida A Tropical Storm Warning is in effect for... * East of Navarre Florida to Indian Pass Florida * Bay St. Louis westward to Grand Isle Louisiana A Storm Surge Warning means there is a danger of life-threatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a life-threatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials. A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. Preparations to protect life and property should be rushed to completion. A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours. For storm information specific to your area, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. DISCUSSION AND OUTLOOK ---------------------- At 400 PM CDT (2100 UTC), the center of Hurricane Sally was located near latitude 29.5 North, longitude 88.1 West. Sally is moving toward the north near 2 mph (4 km/h). A slow northward motion is expected tonight, followed by a slow north-northeastward to northeastward motion on Wednesday and Wednesday night. A slightly faster northeastward motion is expected on Thursday. On the forecast track, the center of Sally will approach the northern Gulf Coast tonight, and make landfall in the hurricane warning area late tonight or Wednesday. Sally is expected to move inland across southeastern Alabama Wednesday night and Thursday. Data from a NOAA Hurricane Hunter aircraft and NWS Doppler radar indicates that maximum sustained winds are near 80 mph (130 km/h) with higher gusts. Little change in strength is forecast until landfall occurs and Sally is expected to be a dangerous hurricane when it moves onshore along the north-central Gulf Coast. Hurricane-force winds extend outward up to 40 miles (65 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km). A NOAA buoy located about 50 miles (80 km) southeast of Mobile, Alabama, recently reported sustained winds of 58 mph (94 km/h) and a gust to 67 mph (108 km/h) within the past couple of hours. An observing site at the Okaloosa Fishing Pier in Florida has reported sustained winds of 44 mph (70 km/h) and a gust to 52 mph (83 km/h). The latest minimum central pressure estimated from reconnaissance aircraft data is 979 mb (28.91 inches). HAZARDS AFFECTING LAND ---------------------- Key messages for Sally can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4 and WMO header WTNT44 KNHC, and on the web at www.hurricanes.gov/text/MIATCDAT4.shtml RAINFALL: Sally is forecast to produce 10 to 20 inches of rainfall with isolated amounts of 30 inches along and just inland of the central Gulf Coast from the Florida Panhandle west of the Apalachicola River to far southeastern Mississippi. Historic life-threatening flash flooding is likely. In addition, this rainfall will lead to widespread moderate to major flooding on area rivers. Sally is forecast to turn inland Wednesday and track across the Southeast producing rainfall of 4 to 8 inches, with isolated maximum amounts of 12 inches, across portions of southeastern Mississippi, southern and central Alabama, central and northern Georgia, and the western Carolinas. Significant flash and urban flooding is likely, as well as widespread minor to moderate flooding on some rivers. STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water could reach the following heights above ground somewhere in the indicated areas if the peak surge occurs at the time of high tide... Dauphin Island, AL to AL/FL Border including Mobile Bay...4-6 ft Mouth of the Mississippi River to Mouth of the Pearl River including Lake Borgne...3-5 ft MS/AL Border to Dauphin Island, AL...3-5 ft AL/FL Border to Okaloosa/Walton County Line, FL including Pensacola Bay and Choctawhatchee Bay...3-5 ft Mouth of the Pearl River to MS/AL Border...2-4 ft Lake Pontchartrain and Lake Maurepas...2-4 ft Okaloosa/Walton County Line, FL to Chassahowitzka, FL including Saint Andrews Bay...1-3 ft Grand Isle, LA to Mouth of the Mississippi River...1-3 ft The deepest water will occur along the immediate coast in areas of onshore winds, where the surge will be accompanied by large and damaging waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office. WIND: Hurricane conditions are expected to begin within the hurricane warning area this evening. Tropical storm conditions are already occurring in portions of the warning areas, and will continue through Wednesday night. TORNADOES: A few tornadoes may occur this evening through Wednesday across portions of the Florida Panhandle and southern Alabama. SURF: Swells from Sally will continue to affect the coast from the Florida Big Bend westward to southeastern Louisiana during the next couple of days. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 700 PM CDT. Next complete advisory at 1000 PM CDT. $$ Forecaster Brown |