Hurricane Idalia's path goes through hot waters in the Gulf of Mexico. That's concerning.

Hurricane Idalia's path toward Florida's coast takes it through a steamy hot tub otherwise known as the Gulf of Mexico.

That's worrisome because hurricanes thrive on warm water. It fuels the heat and water vapor that make the storms stronger and capable of dumping more extreme rainfall. And unseasonably warm water temperatures have lingered in the Gulf for weeks, making it even hotter than normal.

In a worst-case scenario Tuesday, the tropical cyclone will be moving along the coast in water temperatures among the hottest on record in the Gulf as it spins toward landfall overnight or Wednesday morning.

The National Hurricane Center has warned for several days that Idalia was likely to rapidly intensify into a more dangerous storm with higher winds as it travels northward off Florida’s west coast.

The unusual warmth is among a series of marine heat waves covering nearly half the world’s oceans this summer. The heat is blamed on several factors, including the warming climate, which scientists say is contributing to more extreme weather events.

Tracking IdaliaMaps show Hurricane Idalia's path as powerful storm approaches Florida and Georgia

How warm is the Gulf of Mexico? 

Average temperatures in the eastern Gulf on Monday were more than 1.5 degrees above the long-term average for August.

In data from the National Oceanic and Atmospheric Administration, the warmest individual measurement was 91.2 degrees in the Florida Keys. A reading of 89.6 degrees in Panama City was more than 4 degrees warmer than the August average.

Any water temperatures above 82 degrees can help sustain or intensify tropical cyclones, according to the National Aeronautic and Space Administration.

Sea surface temperatures in July were hotter than they had ever been in the satellite record for that time of year, said Derek Manzello, director of NOAA’s Coral Reef Watch. The temperatures are causing coral bleaching and die-offs in the Florida Keys. 

In mid-July, water temperatures in some of the bays off the South Florida coast reached as high as 101.1 degrees.

By mid-August, the Gulf was “the hottest it's been at any point in any year on record by a wide margin, said Michael Lowry, a hurricane scientist with the ABC television affiliate in Miami and a veteran of the National Hurricane Center. Average sea surface temperatures topped 88 degrees for the first time, a full degree over the previous record and more than 2.5 degrees above the 1991-2020 average, Lowry posted on X, formerly Twitter. 

It's not just the Gulf. Globally, the world's oceans were hotter in July 2023 than in any month dating back to 1850, the fourth consecutive month global ocean temperatures were at a record high, NOAA said.

For every 1.8 degrees of warming, a 7% increase is expected in hurricane rainfall rates. A study by researchers at Stony Brook University last year concluded that without climate change, Hurricane Ian would have produced 10% less rainfall.

What’s causing the warmth in the Gulf?

Warmer temperatures overall are responsible for the warm waters, although some scientists say they could be helped along this year by a little early influence from the El Niño in the Pacific Ocean.

July was the warmest month on record in 174 years, NOAA said. It was the 47th consecutive July and 533rd consecutive month with temperatures above the 20th-century average.

Surface waters in the Gulf of Mexico warmed at twice the rate of the global oceans from 1970 to 2020, warming at a rate of about 0.34 degrees per decade, according to a study published this year by the National Centers for Environmental Information and the Northern Gulf Institute. Warming occurs at all depths, but it is greatest in the uppermost 164 feet, the study found. 

A ridge of high pressure over the nation this summer kept temperatures warm, dry and sunny for weeks over Texas, Louisiana and Florida. The heat index in Miami – what the temperature feels like – topped 100 degrees for more than 43 consecutive days, 11 days longer than the record, said Brian McNoldy, a senior research associate at the Rosenstiel School of Marine, Atmospheric and Earth Science at the University of Miami.

Scientists say the marine heat waves in the oceans this summer are the result of several factors coming together, including natural global ocean cycles, long-term climate change and perhaps some influence from El Niño in the Pacific Ocean. The explosion of the Hunga Tonga-Hunga Haʻapai volcano last year and a change in shipping emissions rules also may have some impact.

Have warm waters strengthened other tropical cyclones?

Yes. Warm waters in the Gulf helped Hurricane Michael to rapidly intensify, despite unfavorable atmospheric conditions, a group of scientists concluded in a paper led by Matthieu Le Hénaff at the University of Miami. It became the first Category 5 hurricane to make landfall in the United States in more than 25 years. A Category 5 is the most intense storm on the Saffir-Simpson Scale, a measure of winds during a hurricane.

Hurricane Ian, which briefly reached Category 5 before making landfall in Florida on Sept. 27 last year, also got a boost from the Gulf's warm waters.

Connecting the dots between tropical cyclones and warm oceans

Water temperatures in the upper layers of the ocean are “one of the main driving factors" for storm intensification, said Uchenna Chizaram Nwankwo, an oceanographer with the Gulf of Mexico Coastal Ocean Observing System.

Scientists with the ocean observing system are collaborating this summer with scientists from more than a half-dozen organizations to deploy autonomous vehicles in the Gulf, Caribbean and Atlantic to learn more about storms, gathering and transmitting ocean temperature data in near-real-time to give forecasters a better look at how storms develop.

A focus of the missions is to gather temperature data up to 656 feet deep in the Gulf of Mexico, said Nwankwo, who helps coordinate underwater glider missions in the Gulf. 

Scientists say critical temperature information deployed by the gliders and autonomous drones will help them learn more about how warm water drives rapid intensification, like what they expect to see in Idalia. 

Into the eye of a hurricane: How aircraft and drones penetrate monster storms