A Surprising Factor Helped Supercharge Florida’s Catastrophic 2023 Hurricane Idalia

A previously overlooked factor may have contributed to the debilitating strength of Hurricane Idalia, which cost the United States billions of dollars when it struck in August 2023.

According to a team of researchers that studied the climatic conditions around the storm, the typical cocktail of weather conditions that feed a hurricane doesn’t add up in Idalia’s case. The team’s research analyzing the storm’s evolution was published last month in Environmental Research Letters.

The team found that the usual suspects—warm sea surface temperatures, ocean heat beneath the surface, and low vertical wind shear all played a role in Idalia’s intensification. But the team found that a freshwater plume—including river discharge into the Gulf—created a density gradient between the surface water and deeper, cooler water, allowing Idalia to continue to draw strength from the warmth of the Gulf’s surface.

“Wind wants to mix the water, bringing cold water up to the surface and warm water down to the depths,” said marine scientist Chuanmin Hu, one of the study’s authors, in a NASA Earth Observatory release. “But the density gradient between surface fresh water and deeper salty water makes this difficult.”

Plumes from rivers have historically contributed to the intensification of hurricanes; according to the release, more than two-thirds of storms between 1960 and 2000 that hit Category 5 strength at some point in their cycles passed over the historical region of freshwater plumes.

“If you have a persistent river plume in the right location at the right time,” Hu said, “you may have a perfect storm.”

Hurricane Idalia carved through Florida’s Big Bend before charting a northeasterly course across the American Southeast. The storm quickly swelled from a Category 1 to Category 4 storm, subsiding only slightly into a Category 3 hurricane when it made landfall on August 30, 2023, with maximum sustained winds of nearly 125 miles (205 kilometers) per hour.

The hurricane raised concerns about gas contamination, cut off power for hundreds of thousands of people, and even dropped a tree on the Tallahassee home of Governor Ron DeSantis. The storm shaped up to be the costliest of 2023, tallying a whopping $3.6 billion in damages. The storm departed over the Atlantic on August 31 after cutting across Georgia and the South Carolina coast.

The analysis of contextual factors in Idalia’s formation could help researchers better understand the conditions that foster extreme storms in the future. Consider Hurricane Milton, which shattered records in October 2024 when it intensified from a Category 1 storm to a Category 5 storm in just 7 hours, after feeding on very warm waters in the western Gulf. Category 5 storms are the highest intensity on the Saffir-Simpson hurricane wind scale; to be a Category 5 storm, a system must achieve wind speeds greater than 157 miles per hour (253 kilometers per hour). When Milton touched down in central Florida as a Category 3 storm, it spawned at least three dozen tornadoes across the Sunshine State.

As ocean temperatures continue to break records for warmth, we should expect more extreme and rapidly evolving hurricanes. Hopefully, similar research to the Idalia study will lead to improved forecast models, so that authorities can be prepared for these storms’ landfall. Hurricane season will resume on June 30 and run through November 30.