Hurricane Helene

Hurricane Helene ( heh-LEEN) was a powerful and devastating tropical cyclone that caused widespread catastrophic damage and numerous fatalities across the Southeastern United States in late September 2024. It was the strongest hurricane on record to strike the Big Bend region of Florida, the deadliest Atlantic hurricane since Hurricane Maria in 2017, and the deadliest to strike the mainland U.S. since Hurricane Katrina in 2005.

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.

In advance of Helene's landfall, states of emergency were declared in Florida and Georgia due to the significant impacts expected, including very high storm surge along the coast and hurricane-force gusts as far inland as Atlanta. Hurricane warnings also extended further inland due to Helene's fast motion. The storm caused catastrophic rainfall-triggered flooding, particularly in Western North Carolina, East Tennessee, and southwestern Virginia, and spawned numerous tornadoes. Helene also inundated Tampa Bay, breaking storm surge records throughout the area. The hurricane had a high death toll, causing 252 deaths and inflicting an estimated total of $78.7 billion in damage, making it the fifth-costliest Atlantic hurricane on record adjusted for inflation.

Meteorological history

On September 17, 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.

Preparations

Mexico

Tropical storm warnings were issued on September 24 for the eastern Yucatán Peninsula. Parts of Quintana Roo and Yucatán were placed under a blue alert, indicating indirect impacts. It was later raised to red alert, maximum danger. Cruise ship arrivals in the former state's ports were canceled for September 24 and 25. Tren Maya was also closed. On Isla Mujeres, two shelters were opened. Evacuations were carried out in vulnerable areas. Visitors of Isla Holbox were offered a ferry ride off the island at no cost. Classes were suspended in Quintana Roo.

Caribbean

Cayman Islands

The Cayman Islands were under a tropical storm warning on September 24. The Cayman Islands' Red Cross shelter opened in preparation for the storm; nobody used it. Sandbagging sites opened on Grand Cayman and Cayman Brac. Due to the threat of heavy rainfall, schools in the Cayman Islands were closed on September 23. Charles Kirkconnell International Airport and Owen Roberts International Airport were closed ahead of Helene's arrival. The Cayman Islands Regiment was deployed ahead of the system to help with the preparation and distribution of sandbags. Additionally, a small craft warning was issued for the islands on September 23, with a marine advisory issued the next day. The tropical storm warning was canceled the next day.

Cuba

Tropical storm warnings and hurricane watches were issued for western Cuba. Medical brigades were prepared for flood-prone areas; as heavy rain began to fall, schools and ports were closed, and fishing boats were called in. Due to adverse weather conditions caused by Helene, the Provincial Transport Company of Havana suspended ferry services in Regla. Additionally, the Maritime Administration of Cuba suspended navigation in the Gulf of Batabanó.

United States

Amtrak modified or canceled several of its southeastern train routes between September 27 and October 1 because of the storm.

Florida

Hurricane warnings were issued for the Big Bend area of Florida, and the entire state except the westernmost part of the Florida panhandle was put under a tropical storm warning. In addition, on the evening of September 26, an extreme wind warning was issued for the east part of the Florida panhandle, the first since Hurricane Idalia. On September 23, Ron DeSantis, the governor, issued a state of emergency for 41 of Florida's 67 counties. The next day, this was expanded to 61 counties. U.S. President Joe Biden authorized a federal disaster declaration for 61 counties across Florida. Locally, Volusia County issued a state of emergency. Several sandbagging sites opened up across the state. On September 24, several state parks were closed: four of them in Franklin County, two in Gulf County, and one in Gadsden County.