As Hurricane Idalia charges toward Florida, one factor that could amplify its effects on coastal communities is the unusually warm water in the Gulf of Mexico, which is partly the result of the sultry weather that has been smothering the South all summer.

“Holy cow has it been hot down here,” said Brian Dzwonkowski, a marine scientist at the University of South Alabama and the Dauphin Island Sea Lab. “What does that translate to? Really hot water. And that’s not a good combination for hurricane season.”

Earth’s oceans have been hotter in recent months, by a considerable margin, than at any other time in modern history. In July, a buoy off the Florida coast reported a hot-tub-like reading of 101.1 degrees Fahrenheit, or more than 38 Celsius, a possible world record for sea surface temperatures.

Apart from threatening corals and other sea life, high ocean temperatures can fuel tropical storms and hurricanes. The water warms the air above the sea surface, which endows passing storms with more energy and can allow them to generate fiercer winds. In its 4 a.m. update on Tuesday, the National Hurricane Center said Hurricane Idalia was expected to rapidly intensify into “an extremely dangerous major hurricane” before making landfall in Florida on Wednesday.

“It’s not that those warm temperatures cause the storm to form,” said Allison A. Wing, an associate professor of earth, ocean and atmospheric science at Florida State University. “It’s more that, if a storm is able to form, it can take advantage of those incredibly warm temperatures and become a strong storm.”

The torrid ocean temperatures have made it unusually tricky for forecasters to predict this year’s Atlantic hurricane season. On their own, the warm waters would presage stronger storms on average. But this season is also occurring during an El Niño climate pattern in the Pacific, which is typically associated with less hurricane activity in the Atlantic Ocean.

“The element of having really warm waters in the Atlantic during an El Niño climate pattern, we haven’t really seen that before, not to this extreme,” said Kim Wood, an associate professor of hydrology and atmospheric sciences at the University of Arizona. “And so things don’t quite play out like they might in a more average El Niño year.”