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Hurricane Helene

Category 4 Atlantic hurricane in 2024

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This colored infrared composite image of Hurricane Helene was captured on September 27, 2024, at 01:46 UTC (9:46 PM Eastern Daylight Time on September 26), utilizing the Advanced Baseline Imager (ABI)
ABI imagery from NOAA'S GOES-16 Satellite · Public domain

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The eighth named storm, fifth hurricane, and second major hurricane of the 2024 Atlantic hurricane season, Helene began forming on September 22, 2024 as a broad low-pressure system in the western Caribbean Sea. By September 24, the disturbance had consolidated enough to become a tropical storm as it approached the Yucatán Peninsula, receiving the name Helene from the National Hurricane Center. Weather conditions led to the cyclone's intensification, and it became a hurricane early on September 25. More pronounced and rapid intensification ensued as Helene traversed the Gulf of Mexico the following day, reaching Category 4 intensity on the evening of September 26. Late on September 26, Helene made landfall at peak intensity in the Big Bend region of Florida, near the city of Perry, with maximum sustained winds of 140 mph (220 km/h). Helene weakened as it moved quickly inland before degenerating to a post-tropical cyclone over Tennessee on September 27. The storm then stalled over the state before dissipating on September 29.

Helene's precursor and early stages caused flooding in Nicaragua, Honduras, the Cayman Islands, and the Yucatán Peninsula, where high winds left more than 120,000 customers without electricity in Quintana Roo. Storm surge in Florida caused significant damage from the Tampa Bay area northward. Hillsborough and Pinellas counties combined reported the destruction of at least 419 residences, major damage to at least 18,512 structures, and minor to moderate damage to 13,909 others. Several counties in or near the Big Bend suffered extensive wind impacts. Heavy crop and timber losses occurred over southern Georgia, totaling about $5.5 billion. Tens of thousands of homes and buildings suffered wind damage as far north as the Augusta area, while floodwaters entered at least 200 structures and a number of vehicles in the Atlanta area. Catastrophic flooding and more than 2,000 landslides occurred over the southern Appalachian Mountains, especially North Carolina, due to rainfall totals up to 30.78 in (782 mm) in Busick, North Carolina. In North Carolina, over 125,000 housing units and approximately 822,000 acres (333,000 ha) of timberland suffered some degree of damage. Thousands of miles of bridges and roads were damaged by floodwaters. At least 106 fatalities occurred in North Carolina, far more than any other state. Helene and its remnants also spawned thirty-nine tornadoes across the United States, one of which killed two people in Wheeler County, Georgia. Flooding also impacted Virginia, West Virginia, and Ohio, leaving 12 homes destroyed and 104 others damaged in Pulaski County, Virginia, alone. More than 7.4 million customers lost electricity across the United States. At least 253 deaths and $78.7 billion in damages have been attributed to Helene, making it the second-deadliest hurricane to strike the continental United States in fifty years, after Katrina in 2005, and the deadliest overall since Maria in 2017, as well as being the fifth costliest hurricane in the United States.

Meteorological history

On September 17, 2024, the National Hurricane Center (NHC) highlighted the potential for tropical cyclogenesis in the western Caribbean Sea. Conditions conducive for development of a tropical cyclone resulted from the interaction of the Central American gyre—a broad monsoon low pressure system—and the Madden–Julian oscillation, which reinforced the large-scale cyclonic flow extending from the eastern Pacific Ocean to the western Caribbean Sea. Several days later, on September 22, a broad low-pressure area developed within the western Caribbean. As the system traversed an environment conducive for tropical cyclone development, showers and thunderstorms associated with the disturbance gradually consolidated. Due to the system's imminent threat to land, it was designated Potential Tropical Cyclone Nine on September 23. The next day, Air Force Reserve Hurricane Hunters aircraft and satellite data indicated that a low-level center had formed by 12:00 UTC, leading to the NHC to upgrade the system to Tropical Storm Helene with maximum sustained winds of 45 mph (72 km/h). The system continued strengthening, becoming a hurricane by 12:00 UTC on September 25 as it entered the Gulf of Mexico while turning north. An upper-level trough to its west and a ridge of high pressure located off the Southeastern United States both served to steer the cyclone towards the U.S. Gulf Coast. Helene was an extensive system, with the NHC noting in multiple forecast discussions that the forecast storm radii were "at the 90th percentile of hurricane size at similar latitudes".

After remaining steady in intensity for a while due to its broad size and some entrainment of drier air to its west, Helene rebounded on the morning of September 26. Aided by low mid-level wind shear, high relative humidity, and sea surface temperatures exceeding 86 °F (30 °C) near the Loop Current, the system began to rapidly intensify. An increasingly defined eye developed, and Helene reached Category 2 intensity at 12:00 UTC. By 18:00 UTC, Helene strengthened to a Category 3 major hurricane, with sustained winds up to 120 mph (190 km/h). At 00:00 UTC on September 27, the hurricane attained its peak intensity with maximum sustained winds of 140 mph (220 km/h) and a minimum barometric pressure of 939 millibars (27.73 inHg). Retaining this intensity, it made landfall about 10 miles (16 km) west-southwest of Perry, Florida at 3:10 UTC, becoming the strongest hurricane to strike Florida's Big Bend region since records began in 1900. Rapid weakening occurred as the storm tracked inland, and it weakened to a Category 2 hurricane at 5:00 UTC shortly after crossing into Georgia. Weakening further, it became a tropical storm over east central Georgia at 9:00 UTC. Helene transitioned to a post-tropical cyclone at 18:00 UTC by September 27 in southern Kentucky, with the system losing deep convection and merging with a cut-off low to its west. After executing a slow-cyclonic loop, remnants of Helene dissipated at 18:00 UTC on September 28 over north-central Tennessee.

As Helene moved north into the Southern Appalachian Mountains, the storm would encounter the terrain of the Blue Ridge and Black Mountains. As it passed through, there was a significant and noticeable amplifying of rainfall, as well as a rapid increase in cooling, condensation and precipitation in the region.

Influence of climate change

On October 9, researchers with World Weather Attribution concluded with "high confidence" that Helene was made worse by climate change. In a scientific assessment, researchers found the 2.3 °F (1.3 °C) increase in temperatures due to climate change increased Helene's rainfall by 10% and maximum wind speeds by 11%, or 13.6 mph (22 km/h), as compared to a similar storm in prior cooler conditions.

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