As the North Atlantic hurricane season officially begins, forecasters continue to predict above-average storm activity.
The forecast for 2022 North Atlantic hurricane activity is 18 named storms, eight hurricanes and four major (Category 3 and above) hurricanes, according to storm tracking service Tropical Storm Risk (TSR).
“The last six hurricane seasons have been characterized by above-average activity, and this trend is expected to continue in the 2022 Atlantic hurricane season,” said Allianz Global Corporate & Specialty (AGCS) in its annual hurricane season outlook.
The 2022 hurricane season is expected to be above the 1991-2020 average, with 14-21 tropical storms and six to 10 hurricanes, including three to six major hurricanes, said AGCS, noting that an above-average season would be seven to nine storms reaching hurricane strength and two to four becoming major hurricanes, which is Category 3 or higher.
The 2021 Atlantic hurricane season saw a total of 21 named storms, of which seven were hurricanes (four reached a major hurricane status), with the number of named storms exceeding the average of 14 and the total number of major hurricanes also slightly above the average of three, AGCS said.
On average, the North Atlantic sees 14 named storms, seven hurricanes and three major hurricanes, said catastrophe modeling firm RMS.
Increased Risk Later in Season
While uncertainties still remain, TSR predicted that the 2022 hurricane season will be slightly less active than the two previous years “but may carry an increased risk in the latter part of the storm season.” TSR is operated by EuroTempest, a London-based provider of weather risk management services to the insurance, banking/finance, energy, construction and marine industries.
TSR points out that some Niño forecasts predict a slight strengthening of the current La Niña conditions through the autumn, which would increase the chance of enhanced late-season activity.
The main factors that contributed to the above-average hurricane season in 2021—the third most active season on record—included La Niña, above-normal sea surface temperatures (SSTs) early in the season and above-average West African monsoon rainfall, said AGCS, quoting the National Oceanic and Atmospheric Administration(NOAA).
AGCS said these factors are all expected to be replicated this year because:
NOAA models show at least a 50 percent chance of La Niña conditions persisting during the peak of the Atlantic hurricane season.
While SSTs in the tropical Atlantic are currently near to slightly below normal, they are well above normal in the Caribbean and in the subtropical North Atlantic, which correlates relatively well with what is typically observed in active Atlantic hurricane seasons.
An enhanced West African monsoon supports stronger African easterly waves that, in turn, seed many of the strongest, longest-lived hurricanes, according to AGCS, quoting NOAA.
Favorable Conditions for Storm Formation
Forecasts of an above-average hurricane season “reflect the state of the two main oceanic and climate factors that historically dictate hurricane activity in the basin: the El Niño Southern Oscillation (ENSO) and sea surface temperatures in the equatorial North Atlantic. ENSO is forecast to remain in a La Niña phase through the summer,” according to James Cosgrove, senior modeler at RMS, in an emailed statement.
“Such conditions reduce the vertical wind shear across the North Atlantic, which typically enhances hurricane activity by providing a more favorable atmosphere for storm development and intensification,” he said. “Moreover, sea surface temperatures in the tropical North Atlantic are expected to remain above average throughout the summer, which also typically increases hurricane activity in the basin.”
Long-term statistics indicate that the probability of a hurricane making landfall in the U.S. increases during more active seasons, but there are exceptions, Cosgrove said.
For example, 2010 was a particularly active year, but only one tropical storm made U.S. landfall. “Conversely, Hurricane Andrew, one of the most intense and costliest hurricanes in U.S. history, was one of only seven storms to develop during the quiet 1992 season. It only takes one landfalling storm to make the season a memorable one,” he added.
Longer Hurricane Seasons
While the North Atlantic hurricane season runs for six months from June 1 through to Nov. 30, AGCS said, recent Atlantic hurricane seasons have seen the first tropical storms form before the official start date. As a result, the NOAA Hurricane Center has contemplated moving the start date to May 15.
The extension of hurricane activity could be attributed to the development of advanced observational technologies, which can identify weaker storms that never come close to any landmass, adding to tropical storm counts, said AGCS.
However, this extension of seasonal storm activity is more likely driven by higher sea surface temperatures, said Bastian Manz, senior climate risk analyst at Allianz Re.
“Tropical storms can only form and sustain themselves for longer periods where ocean temperatures exceed 27°C [80.6°F],” he added.
“Anthropogenic (manmade) global warming has increased atmospheric temperature by 1.1°C since 1880, with most of the net excess heat stored in the world’s oceans, including the North Atlantic. This has increased the duration of hurricane-supporting SSTs as well as the geographical spread of where they might occur.”
Manz acknowledged there is no clear scientific consensus on whether climate change will bring an increase in the frequency of tropical storms. “However, there is more certainty that high-intensity storms will become more frequent, indicating the potential for greater damage.”
He said that hurricanes are becoming harder to predict as a result of the phenomenon of “rapid intensification,” where a storm intensifies significantly in a short period of time. “The wind speeds of Hurricane Ida [in 2021] increased by 55 mph in the 24 hours before landfall in Louisiana,” Manz confirmed.
“Scientists believe climate change will make hurricanes wetter, increasing the risk of secondary perils like flooding and storm surge,” he added.
Hurricanes today are causing rainfall that is 11 percent more intense than in a pre-industrial climate, Manz said, quoting a study from Nature.
“This is compounded by hurricanes slowing down in their forward movement, so rainfall accumulates in individual locations and causes extensive flooding,” he said, pointing to the example of Hurricane Harvey, which caused devastating floods after stalling over Houston in 2017. Manz said that research has indicated that Harvey’s “unprecedented downpour” was made three times more likely as a result of climate change.