|Hurricane Ida, Tropical Storm Julian and Tropical Depression Ten - which intensified into Tropical Storm Kate on August 30 - as shown from NOAA's GOES-16 satellite on August 29, 2021.
For the seventh year in a row, University of Arizona hurricane forecasters say to prepare for an above-average hurricane season, which runs from June 1 through Nov. 30. However, this year isn't expected to be as active as recent years.
The experts' forecast, released this month, shows 14 named storms and seven hurricanes developing over the Atlantic Ocean. Three of those seven hurricanes are expected to develop into major hurricanes – which are classified as category 3 or above. The UArizona experts also predict an accumulated cyclone energy, or ACE, index of 129 units. The ACE index provides a value for the combined strength and duration of a storm.
These predictions are only slightly higher than the seasonal median since 1980, which is 13 named storms and seven hurricanes, two of which are major hurricanes, and an ACE index of 107 units.
Professor of atmospheric sciences Xubin Zeng and former graduate student Kyle Davis developed their predictive model in 2014. It has since become one of the most accurate in the world for seasonal hurricane forecasting. It combines seasonal forecasts of sea surface temperature from the European Centre for Medium-Range Weather Forecasts with machine learning and the researchers' own understanding of hurricanes.
When sea surface water is warm, storms can increase evaporation from the water, which creates moisture in the air. In combination with the right wind conditions, storms become hurricanes and the condensation of moisture releases heat energy to fuel the storm.
"Sea surface temperatures play a big role, and this year, the sea surface temperatures over the Atlantic Ocean are only slightly warmer than usual," said Zeng, who is also director of the university's Climate Dynamics and Hydrometeorology Center, and is the Agnes N. Haury Endowed Chair in Environment in the College of Science's Department of Hydrology and Atmospheric Sciences.
Pacific Ocean surface temperatures are nearly average this year as well, which also contributes to the near-average hurricane prediction.
Unlike other hurricane forecasters, Zeng and Davis don't use wind speed and direction data in their prediction models.
"We feel the seasonal forecasting of wind is not as reliable as prediction of seas' surface temperatures," Zeng said.
Zeng and Davis will update their predictions again in early June based on updated sea surface temperatures.
In 2021, the team predicted 18 named storms, eight hurricanes, four major hurricanes, and an ACE index of 137 units. These forecasts were remarkably accurate compared with the actual numbers in 2021 of 21 named storms, seven hurricanes, four major hurricanes and an ACE index of 146 units.
Each year, Zeng and Davis share their predictions with the public and government agencies for consideration.
"In the end, what matters is how many hurricanes make landfall," Zeng said. "With the growth in coastal population and regional wealth, even a single landfalling major hurricane could cause substantial damage."
Source/Credit: University of Arizona | Mikayla Mace Kelley