Early forecasts from experts at AccuWeather, Colorado State University (CSU), National Oceanic and Atmospheric Administration(NOAA), North Carolina State University (NCSU), Tropical Storm Risk(TSR), and the UK Met Office all point towards an exceptionally active 2024 Atlantic hurricane season. Unusually warm sea surface temperatures (SSTs) in the tropical Atlantic, coupled with La Niña conditions (see panel) expected to develop this summer, are creating prime favorable conditions for the development of tropical cyclones in the Atlantic.

The table below summarizes the predicted number of tropical storm events for 2024 by these six organizations. Based on their forecasts, the 2024 season is expected to be well above the 1991-2020 average, with 15 to 28 tropical storms, eight to 16 hurricanes, and two to seven major hurricanes. The NOAA has issued its highest-ever pre-season forecast. The EuroTempest’s Tropical Storm Risk 2024 report predicts an exceptionally active Atlantic hurricane season in 2024 and uncertainties remain around factors like the El Niño Southern Oscillation, or ENSO (see panel), and outbreaks of dry, dusty Saharan air, among other factors.

Predictions by institution

Outlook: well above average

Wind shear and SSTs are two driving conditions for the formation of hurricanes. Wind shear is a measure of how much wind speed and direction vary with height. The total vertical wind shear is affected by ENSO. As of April 2024, the tropical Pacific is characterized by El Niño conditions. However, by the peak of the Atlantic hurricane season (August to October), it is expected these conditions will have shifted to La Niña, which typically means a decrease in the vertical wind shear. With milder upper-level winds, hurricane formation in the Atlantic basin is favored.

For a cyclone to form, SSTs need to be above 26°C. This year’s SSTs in the tropical Atlantic are much warmer than normal, which is expected to favor the formation of hurricanes. In mid-May 2024, the SSTs in the North Atlantic were as high as the average SSTs (1982-2011) by mid-June. Most Atlantic SSTs registered in 2024 have been significantly warmer than in the last 44 years. Warmer-than-usual SSTs not only affect the probability of hurricane formation, but they could also influence landfall risk. During years with warm SSTs, the US Gulf Coast tends to see an increase in the risk of tropical storm landfalls, while the south-east coast of the US sees an increased risk of hurricane landfalls.

Source data: Climate Reanalyzer, Climate Change Institute, University of Maine

2023 in review – the season of ‘fish storms’

The 2023 North Atlantic hurricane season began with an unexpected early event: an unnamed subtropical storm formed near the north-eastern coast of the US in January. The season turned out to be more active than expected, with 20 named storms, exceeding pre-season forecasts by six. Seven of these reached hurricane strength, and three became major hurricanes: Franklin (Category 4), Idalia (weakening to a Category 3 at landfall), and Lee (Category 5). Despite it being an above-average season, only eight storms made landfall in 2023 and only tropical storms Harold and Ophelia and Hurricane Idalia made landfall in the US. Most of the storms were therefore referred to as “fish storms” – storms that stay out at sea and pose no direct threat to land, but the 2023 season still registered billions of dollars in insured losses and economic losses. It was also still the fourth most active on record.

2023 hurricane season in a nutshell

  • 2023 was the fourth most active year on record with 20 named storms after 2020, 2005 and 2021. This means three of the most active seasons on record have occurred in the past four years.
  • Accumulated Cyclone Energy (ACE) of 146 was generated during 2023, making it an above-normal season by NOAA’s definition (ACE is a measure of a named storm’s potential for wind and storm surge destruction). The Atlantic has not seen a below-average season per NOAA’s definition since 2015.
  • 13 named storms formed from August 20 to September 28 – the most ever recorded during this period.  
  • For the first time since record-keeping began, two named storms, Bret and Cindy, formed in June, hinting at a potential shift in early-season storm patterns.
  • Two hurricanes, Franklin and Idalia, simultaneously reached wind speeds exceeding 177km/h (110mph), a phenomenon not seen since 1950.
  • According to NOAA’s National Hurricane Center Tropical Cyclone Report, Hurricane Lee’s wind speed surged by 130km/h (81mph) in just 24 hours, propelling it to Category 5 status (one of only seven hurricanes in the satellite era to achieve such rapid intensification) and peak wind speeds of 270km/h (154mph).
  • A week after Hurricane Lee, Tropical Storm Ophelia hit the town of Emerald Isle in North Carolina with strong winds of 115km/h (70mph), bringing relentless rain and flooding from coastal surges and overflowing rivers across the state.
  • Tropical Storm Sean formed late on October 10 and far east in the Atlantic, an area normally too cool for storms. Despite this unusual development, it remained weak with winds only reaching 75km/h (47mph).
  • Hurricane Tammy made a late appearance, developing on October 18 and briefly reaching Category 2 strength. It caused minor damage in the Leeward Islands and Bermuda before dissipating.

Deep dive: Hurricane Idalia

In late August, Hurricane Idalia made landfall in Florida’s Big Bend region as a Category 3 storm, becoming the first major hurricane to make landfall in that area since records began in 1842. Estimated insured losses from Idalia are reported in some cases to be as high as $3bn to $5bn. Despite weakening after landfall, Idalia’s initial intensity and rapid forward speed propelled it across northern Florida and into southern Georgia within just nine hours, maintaining hurricane strength.

Idalia unleashed storm surges with inundation levels in coastal areas ranging from 2m-3.7m (7ft-12ft), among the highest recorded since the 1993 Storm of the Century (a massive storm that struck the East Coast of the US, causing high winds, extreme coastal flooding, and blizzards). Heavy rainfall from Idalia led to flash flooding in some areas, with accompanying heavy rainfall and strong winds also impacting Georgia. As Idalia weakened, it continued its path into South Carolina as a tropical storm.

Atlantic hurricane seasons by numbers

Atlantic hurricane season in numbers 2000 to 2023 and 2024 average forecasts: tropical storms, hurricanes, and major hurricanes. ‘Average’ hurricane season considers the period 1991-2020, according to the National Oceanic and Atmospheric Administration (NOAA). Source data: National Hurricane Center/NOAA; graphic by Allianz Commercial

Accuracy of pre-season forecasts in 2023

Over 25 predictions were made for the 2023 season, with some expecting a quiet year (Mexico’s Servicio Meteorológico Nacional predicted five hurricanes) and others braced for more activity (the UK Met Office reckoned on 11 hurricanes).

It all came down to a battle between two weather giants: warm ocean temperatures, perfect for brewing storms, were at odds with El Niño, a climate pattern which usually reduces hurricane activity. As summer approached and more data became available, forecasters adjusted their predictions. The warmer-than-expected seas seemed to win out, with most predictions increasing. NOAA settled on a “near-normal” season, while CSU went for “very active.”

As we stand on the brink of an active season, it is essential for businesses to revisit risk management strategies and strengthen resilience measures. A single storm hitting in the “right” location can be enough for the insurance market to experience considerable losses. Regardless of the overall activity level predicted for 2024, coastal businesses and residents should remember: it only takes one landfalling hurricane to significantly disrupt lives and property.

If you are in the US, visit National Hurricane Preparedness for more information about how to determine your risk and develop an evacuation plan.

ABOUT THE AUTHOR

Thomas Varney

Thomas Varney is the North American regional manager of Allianz Risk Consulting. Allianz Risk Consulting publishes a series of risk bulletins and checklists to help you protect your people, property, and business, including: Windstorm Checklist, Flood Checklist, and Hailstorm Checklist.

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