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Tropical Storm Helene Forecast Discussion Number 5
2024-09-24 16:59:25| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Tue Sep 24 2024 000 WTNT44 KNHC 241459 TCDAT4 Tropical Storm Helene Discussion Number 5 NWS National Hurricane Center Miami FL AL092024 1100 AM EDT Tue Sep 24 2024 An Air Force Reserve Hurricane Hunter measured peak 925-mb flight-level winds of 52 kt to the northeast of the center, which supports an initial intensity of 40 kt. Dropsonde data also indicated that the central pressure is down to 1000 mb. Very recently, data from the plane and one-minute visible satellite imagery indicate that the center has become better defined. Based on these data, the system is being designated as Tropical Storm Helene at this time. Helene is moving a little faster toward the northwest (310/10 kt) as it moves around a mid-level area of high pressure located over Florida and the Southeastern U.S. The high is expected to slide eastward through Wednesday as a deep-layer trough digs southward over the Lower Mississippi Valley. This pattern evolution should cause the system to turn northward and north-northeastward late Wednesday into Thursday. The track guidance is very tightly clustered, which would normally imply high forecast confidence. However, depending on exactly where the center forms could end up shifting the entire guidance suite in future cycles, so it is imperative to not focus on specific landfall locations this far in the future. Satellite trends suggest that the shear over the system is beginning to decrease, and model guidance continues to show relatively low to moderate shear for the next 48 hours or so. In addition, oceanic heat content values are very high, and the system will be moving through an environment of upper-level divergence. Therefore, significant strengthening is anticipated, and the NHC intensity forecast shows the system reaching a peak intensity around 100 kt in 48 hours while over the eastern Gulf of Mexico. There could be some increase in shear around the time the system reaches the coast, given the system's large size, it might only weaken slowly. As a result, there is still a risk that the system could reach the coast as a major hurricane. Helene's forecast radii are at the 90th percentile of hurricane size at similar latitudes. Due to the forecast large size of this system, storm surge, wind, and rainfall impacts will extend well away from the center, particularly on the east side. In addition, the fast forward speed while it crosses the coast will likely result in farther inland penetration of strong winds over parts of the southeastern United States after landfall. KEY MESSAGES: 1. Helene is forecast to intensify and be near hurricane strength when it reaches the far northwestern Caribbean Sea early Wednesday. Tropical storm conditions are expected over portions of western Cuba and the northeastern coast of the Yucatan Peninsula with hurricane conditions possible. 2. Helene is expected to rapidly intensify over the eastern Gulf of Mexico and be a major hurricane when it approaches the northeastern Gulf Coast on Thursday. The risk of impacts from life-threatening storm surge and damaging hurricane-force winds continues to increase along the coast of the Florida Panhandle and the Florida west coast. Hurricane and Storm Surge Watches are in effect for much of that area and residents in those areas should follow advice given by local officials. 3. Helene will bring heavy rain to portions of the western Caribbean, which will cause considerable flooding and mudslides across western Cuba. Heavy rainfall will likely result in locally considerable flash and urban flooding across portions of Florida, with isolated flash and urban flooding possible across the Southeast, Southern Appalachians, and the Tennessee Valley Wednesday through Friday. Minor to isolated moderate river flooding will be possible. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 19.5N 84.3W 40 KT 45 MPH 12H 25/0000Z 20.3N 85.2W 50 KT 60 MPH 24H 25/1200Z 21.5N 86.3W 65 KT 75 MPH 36H 26/0000Z 23.2N 86.3W 80 KT 90 MPH 48H 26/1200Z 25.9N 85.4W 100 KT 115 MPH 60H 27/0000Z 29.7N 84.3W 100 KT 115 MPH 72H 27/1200Z 33.9N 83.9W 45 KT 50 MPH...INLAND 96H 28/1200Z 39.7N 86.8W 20 KT 25 MPH...POST-TROPICAL 120H 29/1200Z...DISSIPATED $$ Forecaster Berg
Category:Transportation and Logistics
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Summary for Tropical Storm Helene (AT4/AL092024)
2024-09-24 16:58:55| National Hurricane Center (Atlantic)
...TROPICAL STORM HELENE FORMS OVER THE NORTHWESTERN CARIBBEAN SEA... ...HURRICANE AND STORM SURGE WATCHES REMAIN IN EFFECT FOR PORTIONS OF THE FLORIDA GULF COAST... As of 11:00 AM EDT Tue Sep 24 the center of Helene was located near 19.5, -84.3 with movement NW at 12 mph. The minimum central pressure was 1000 mb with maximum sustained winds of about 45 mph.
Category: Transportation and Logistics
Tropical Storm Helene Public Advisory Number 5
2024-09-24 16:58:55| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Tue Sep 24 2024 000 WTNT34 KNHC 241458 TCPAT4 BULLETIN Tropical Storm Helene Advisory Number 5 NWS National Hurricane Center Miami FL AL092024 1100 AM EDT Tue Sep 24 2024 ...TROPICAL STORM HELENE FORMS OVER THE NORTHWESTERN CARIBBEAN SEA... ...HURRICANE AND STORM SURGE WATCHES REMAIN IN EFFECT FOR PORTIONS OF THE FLORIDA GULF COAST... SUMMARY OF 1100 AM EDT...1500 UTC...INFORMATION ----------------------------------------------- LOCATION...19.5N 84.3W ABOUT 180 MI...295 KM ESE OF COZUMEL MEXICO ABOUT 170 MI...275 KM SSE OF THE WESTERN TIP OF CUBA MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H PRESENT MOVEMENT...NW OR 310 DEGREES AT 12 MPH...19 KM/H MINIMUM CENTRAL PRESSURE...1000 MB...29.53 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: A Tropical Storm Warning has been issued for the Lower Florida Keys west of the Seven Mile Bridge and for the Dry Tortugas. A Tropical Storm Watch has been issued for the Middle Florida Keys from the Seven Mile Bridge to the Channel 5 Bridge. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Watch is in effect for... * Indian Pass southward to Flamingo * Tampa Bay * Charlotte Harbor A Hurricane Watch is in effect for... * Cabo Catoche to Tulum, Mexico * Cuban province of Pinar del Rio * Englewood to Indian Pass * Tampa Bay A Tropical Storm Warning is in effect for... * Dry Tortugas * Lower Florida Keys west of the Seven Mile Bridge * Grand Cayman * Rio Lagartos to Tulum, Mexico * Cuban provinces of Artemisa, Pinar del Rio, and the Isle of Youth A Tropical Storm Watch is in effect for... * Middle Florida Keys from the Seven Mile Bridge to the Channel 5 Bridge * Flamingo to south of Englewood * West of Indian Pass to Walton Bay County line 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 Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within the next 36 hours. 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, generally within 48 hours. Wind and storm surge warnings will likely be required for the U.S. 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 1100 AM EDT (1500 UTC), the center of Tropical Storm Helene was located near latitude 19.5 North, longitude 84.3 West. Helene is moving toward the northwest near 12 mph (19 km/h), and this general motion is expected to continue through early Wednesday. A northward to north-northeastward motion at a faster forward speed is expected on Wednesday and Thursday. On the forecast track, the center of Helene will move across the far northwestern Caribbean Sea through tonight, and then move across the eastern Gulf of Mexico Wednesday and Thursday, potentially reaching the Gulf coast of Florida late Thursday. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the system has acquired a well-defined center of circulation, and maximum sustained winds have increased to near 45 mph (75 km/h) with higher gusts. Additional strengthening is forecast, and Helene is expected to become a hurricane on Wednesday. Continued strengthening is anticipated after that time, and Helene could become a major hurricane on Thursday. Tropical-storm-force winds extend outward up to 140 miles (220 km) to the east of the center. Data from the Hurricane Hunter aircraft indicate that the minimum central pressure is 1000 mb (29.53 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 RAINFALL: Helene is expected to produce total rain accumulations of 4 to 8 inches over western Cuba and the Cayman Islands with isolated totals around 12 inches. Over the eastern Yucatan Peninsula, 4 to 6 inches of rain are expected with isolated totals over 8 inches. This rainfall brings a risk of considerable flooding. Over the Southeastern U.S., Helene is expected to produce total rain accumulations of 4 to 8 inches with isolated totals around 12 inches. This rainfall will likely result in areas of considerable flash and urban flooding, with minor to moderate river flooding likely, and isolated major river flooding possible. 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. 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... Ochlockonee River, FL to Chassahowitzka, FL...10-15 ft Chassahowitzka, FL to Anclote River, FL...6-10 ft Indian Pass, FL to Ochlockonee River, FL...5-10 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 Bonita Beach, 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 possible within the watch areas in Cuba and Mexico by early Wednesday. Hurricane conditions are possible within the U.S. watch areas Wednesday night and early Thursday. Tropical storm conditions are expected in the warning areas in the Cayman Islands, Cuba, and Mexico today. Tropical storm conditions are expected in the warning area in the Lower Florida Keys beginning on Wednesday, and are possible in the watch area in the Middle Florida Keys beginning late Wednesday. 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 on Wednesday 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 200 PM EDT. Next complete advisory at 500 PM EDT. $$ Forecaster Berg
Category: Transportation and Logistics