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Hurricane Helene Forecast Discussion Number 9
2024-09-25 16:57:58| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Wed Sep 25 2024 000 WTNT44 KNHC 251457 TCDAT4 Hurricane Helene Discussion Number 9 NWS National Hurricane Center Miami FL AL092024 1000 AM CDT Wed Sep 25 2024 Air Force Reserve and NOAA Hurricane Hunter aircraft have been investigating Helene, with each plane recently measuring peak flight-level winds of 81 kt and 78 kt, respectively. Helene has therefore become a hurricane with an estimated intensity of 70 kt. Dropsonde data also indicate that the pressure has fallen to about 979 mb. Radar data from Mexico and Cuba, as well as reconnaissance reports, indicate that Helene has formed a partial, elliptical eyewall that is open on the east side. Helene has turned north-northwestward (330/9 kt) and is expected to turn northward and north-northeastward later today and tonight, bringing the center to the coast of the Florida Big Bend Thursday evening. After landfall, Helene is expected to interact with a deep-layer trough over the Lower Mississippi Valley and swing back to the northwest and stall near the Tennessee Valley late Friday into the weekend. The track guidance remains tightly clustered, and the NHC forecast is generally just an update of the previous prediction. It is still too soon at this point to be overly focused on an exact landfall location and time, since NHC track forecasts can be off by an average of 60 nm at the 36-hour forecast time. Helene is expected to move through/over an environment of relatively low shear, strong upper-level divergence, and sea surface temperatures of 29-31 degrees Celsius, all of which should foster additional strengthening. Rapid Intensification (RI) indices indicate a high chance of RI during the next 24 hours, and as a result the NHC intensity forecast shows Helene becoming a major hurricane by Thursday morning. There is still some uncertainty on exactly how strong Helene will get, and upward adjustments to the forecast intensity could be required in subsequent advisories if Helene rapidly intensifies more than forecast. Regardless, Helene is forecast to be a large major hurricane when it reaches the Big Bend coast of Florida. As a result, storm surge, wind, and rainfall impacts will likely extend well away from the center and outside the forecast cone, particularly on the east side. In addition, the fast forward speed while Helene crosses the coast will likely result in farther inland penetration of strong winds over parts of the southeastern United States after landfall, including strong gusts over higher terrain of the southern Appalachians. KEY MESSAGES: 1. Hurricane and tropical storm conditions are expected over northeastern portions of the Yucatan Peninsula of Mexico today where Tropical Storm and Hurricane Warnings are in effect. Tropical storm conditions are occurring over portions of western Cuba within the Tropical Storm Warning area, and hurricane conditions are possible today within the Hurricane Watch area. 2. Due to the large size of Helene, there is a danger of life-threatening storm surge along the entire west coast of the Florida Peninsula and Florida Big Bend. The highest inundation of greater than 10 ft is expected along the Florida Big Bend coast. Residents in those areas should follow advice given by local officials and evacuate if told to do so. 3. Devastating hurricane-force winds are expected across portions of northern Florida and southern Georgia where the core of Helene moves inland. Preparations to protect life and property should be completed by early Thursday since tropical storm conditions are expected to begin within these areas on Thursday. Because of Helenes expected fast forward speed, damaging and life-threatening wind gusts, are expected to penetrate well inland over portions of the southeastern United States, including in the higher terrain of the southern Appalachians. 4. Helene will bring heavy rain to portions of the western Caribbean with potentially significant flooding across western Cuba and the northeastern Yucatan Peninsula into early Thursday. Considerable and potentially life-threatening flash and urban flooding is expected across portions of northwestern and northern Florida, the Southeast, southern Appalachians, and the Upper Tennessee Valley Wednesday through Friday. This includes the risk of landslides across the southern Appalachians. Widespread minor to moderate river flooding is likely, and isolated major river flooding is possible. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 21.6N 86.3W 70 KT 80 MPH 12H 26/0000Z 23.0N 86.4W 85 KT 100 MPH 24H 26/1200Z 25.7N 85.7W 105 KT 120 MPH 36H 27/0000Z 29.7N 84.6W 110 KT 125 MPH 48H 27/1200Z 34.3N 85.0W 50 KT 60 MPH...INLAND 60H 28/0000Z 36.6N 86.9W 30 KT 35 MPH...POST-TROP/INLAND 72H 28/1200Z 36.9N 87.8W 20 KT 25 MPH...POST-TROP/INLAND 96H 29/1200Z 36.6N 87.9W 15 KT 15 MPH...POST-TROP/INLAND 120H 30/1200Z...DISSIPATED $$ Forecaster Berg
Category:Transportation and Logistics
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Summary for Hurricane Helene (AT4/AL092024)
2024-09-25 16:57:28| National Hurricane Center (Atlantic)
...HELENE BECOMES A HURRICANE... ...EXPECTED TO BRING LIFE-THREATENING STORM SURGE, DAMAGING WINDS, AND FLOODING RAINS TO A LARGE PORTION OF FLORIDA AND THE SOUTHEASTERN UNITED STATES... As of 10:00 AM CDT Wed Sep 25 the center of Helene was located near 21.6, -86.3 with movement NNW at 10 mph. The minimum central pressure was 979 mb with maximum sustained winds of about 80 mph.
Category: Transportation and Logistics
Hurricane Helene Public Advisory Number 9
2024-09-25 16:57:28| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Wed Sep 25 2024 000 WTNT34 KNHC 251457 TCPAT4 BULLETIN Hurricane Helene Advisory Number 9 NWS National Hurricane Center Miami FL AL092024 1000 AM CDT Wed Sep 25 2024 ...HELENE BECOMES A HURRICANE... ...EXPECTED TO BRING LIFE-THREATENING STORM SURGE, DAMAGING WINDS, AND FLOODING RAINS TO A LARGE PORTION OF FLORIDA AND THE SOUTHEASTERN UNITED STATES... SUMMARY OF 1000 AM CDT...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...21.6N 86.3W ABOUT 85 MI...135 KM NNE OF COZUMEL MEXICO ABOUT 500 MI...810 KM SSW OF TAMPA FLORIDA MAXIMUM SUSTAINED WINDS...80 MPH...130 KM/H PRESENT MOVEMENT...NNW OR 330 DEGREES AT 10 MPH...17 KM/H MINIMUM CENTRAL PRESSURE...979 MB...28.91 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: The Tropical Storm Warning has been extended northward along the coasts of Georgia and South Carolina to South Santee River, and westward along the Florida Gulf coast to the Okaloosa/Walton County Line. A Storm Surge Watch has been issued from Mexico Beach to Indian Pass, Florida. A Tropical Storm Watch has been issued along the coast of South Carolina north of South Santee River to Little River Inlet. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for... * Indian Pass southward to Flamingo * Tampa Bay * Charlotte Harbor A Hurricane Warning is in effect for... * Anclote River to Mexico Beach * Cabo Catoche to Tulum, Mexico including Cozumel A Storm Surge Watch is in effect for... * West of Indian Pass to Mexico Beach A Hurricane Watch is in effect for... * Cuban province of Pinar del Rio * Englewood to Anclote River, including Tampa Bay A Tropical Storm Warning is in effect for... * Florida Keys, including the Dry Tortugas * Flamingo to Anclote River, including Tampa Bay * West of Mexico Beach to the Okaloosa/Walton County Line * Flamingo northward to South Santee River * Lake Okeechobee * Rio Lagartos to Cabo Catoche, Mexico * Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth A Tropical Storm Watch is in effect for... * North of South Santee River to Little River Inlet 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. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. 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 the next 36 hours. A Storm Surge Watch means there is a possibility of life- threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. A Hurricane Watch means that hurricane conditions are possible within the watch area. A watch is typically issued 48 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area. Additional watches or warnings may be required later today. For storm information specific to your area in the United States, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. For storm information specific to your area outside of the United States, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 1000 AM CDT (1500 UTC), the center of Hurricane Helene was located near latitude 21.6 North, longitude 86.3 West. Helene is moving toward the north-northwest near 10 mph (17 km/h). A turn toward the north and north-northeast with an increase in forward speed is expected later today through Thursday, bringing the center of Helene across the eastern Gulf of Mexico and to the Florida Big Bend coast by Thursday evening. After landfall, Helene is expected to slow down and turn toward the northwest over the southeastern United States Friday and Saturday. Data from NOAA and Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds have increased to near 80 mph (130 km/h) with higher gusts. Additional strengthening is forecast, and Helene is expected to be a major hurricane when it reaches the Florida Big Bend coast Thursday evening. Weakening is expected after landfall, but Helene's fast forward speed will allow strong, damaging winds, especially in gusts, to penetrate well inland across the southeastern United States, including over the higher terrain of the southern Appalachians. Hurricane-force winds extend outward up to 25 miles (35 km) from the center and tropical-storm-force winds extend outward up to 275 miles (445 km). The minimum central pressure based on dropsonde is 979 mb (28.91 inches). HAZARDS AFFECTING LAND ---------------------- Key Messages for Helene can be found in the Tropical Cyclone Discussion under AWIPS header MIATCDAT4 and WMO header WTNT44 KNHC and on the web at hurricanes.gov/text/MIATCDAT4.shtml 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... Carrabelle, FL to Chassahowitzka, FL...10-15 ft Chassahowitzka, FL to Anclote River, FL...6-10 ft Indian Pass, FL to Carrabelle, FL...6-10 ft Anclote River, FL to Middle of Longboat Key, FL...5-8 ft Tampa Bay...5-8 ft Middle of Longboat Key, FL to Englewood, FL...4-7 ft Englewood, FL to Flamingo, FL...3-5 ft Charlotte Harbor...3-5 ft For a complete depiction of areas at risk of storm surge inundation, please see the National Weather Service Peak Storm Surge Graphic, available at hurricanes.gov/graphics_at4.shtml?peakSurge. Storm surge could raise water levels by as much as 2 to 4 feet above normal tide levels in areas of onshore winds along the southern coast of Pinar del Rio, Cuba, including the Isle of Youth. Storm surge could raise water levels by as much as 2 to 4 feet above ground level in areas of onshore winds within the warning area along the east coast of the Yucatan Peninsula. WIND: Hurricane conditions are expected within the U.S. hurricane warning area late Thursday, with tropical storm conditions beginning Thursday morning. Tropical storm conditions are expected in southern Florida later today and will spread northward across the rest of Florida, Georgia, and South Carolina through Thursday. Tropical storm conditions are possible within the tropical storm watch area in South Carolina beginning on Thursday. Hurricane conditions, especially in gusts, are expected in the hurricane warning area in Mexico during the next several hours. Tropical storm conditions are occurring in the warning area in Cuba, and hurricane conditions are possible for the western portion of Cuba today. RAINFALL: Helene is expected to produce total rain accumulations of 4 to 8 inches over western Cuba, the Cayman Islands, and the northeast Yucatan Peninsula, with isolated totals around 12 inches. This rainfall brings a risk of considerable flooding. Over the Southeastern U.S. into the Southern Appalachians, Helene is expected to produce total rain accumulations of 5 to 10 inches with isolated totals around 15 inches. This rainfall will likely result in areas of considerable flash and urban flooding, with areas of significant river flooding. Landslides are possible in areas of steep terrain in the southern Appalachians. For a complete depiction of forecast rainfall associated with Helene, please see the National Weather Service Storm Total Rainfall Graphic, available at hurricanes.gov/graphics_at4.shtml?rainqpf and the Flash Flood Risk graphic at hurricanes.gov/graphics_at4.shtml?ero. TORNADOES: A tornado or two may occur tonight over parts of the Florida Peninsula and southern Alabama. The risk of tornadoes will increase on Thursday, expanding northward across Florida into parts of Georgia and South Carolina. SURF: Swells generated by Helene will affect the southern coast of Cuba and the Yucatan Peninsula of Mexico during the next couple of days. Swells will spread northward toward the west coast of Florida and the northeastern Gulf Coast later today and Thursday. 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 100 PM CDT. Next complete advisory at 400 PM CDT. $$ Forecaster Berg
Category: Transportation and Logistics