Top 5 reasons Idalia stands apart from other storms

• Extreme heat associated with stubborn, humid heat domes throughout the spring and summer culminated in record-shattering temperatures along the Gulf Coast over the weekend.
• The hot waters helped helped aggravate the heat in coastal cities, contributing to the hottest temperatures on record over the weekend in places like New Orleans, which reached 105°F, and Houston, which hit 109°F.
• The waters of the northeastern Gulf of Mexico, which are about 3°F above average, inched higher as a consequence of the most recent heat wave.

Between the lines: Second, the storm is likely to stand apart from many recent landfalling hurricanes — including some that intensified until they crossed the coast — in that it will it will encounter unusually hot ocean temperatures all along the way.

• These Jacuzzi-like waters exist both in deeper parts of the Gulf, including a section of the Gulf Loop current in the eastern Gulf, and in shallow waters closer to land, off Florida's Big Bend.
• Unusually warm waters of 88°F extend down to about 165 feet below the surface in areas where the center of Idalia is forecast to traverse, according to Kim Wood, an atmospheric scientist at the University of Arizona.
• This is rarely witnessed — let alone encountered — by an intensifying hurricane.

Context: Third, the high ocean temperatures are a clear connection between the storm's rapid intensification and human-caused climate change, according to Jim Kossin, of the University of Wisconsin-Madison and the nonprofit First Street Foundation.

• He said the ocean heat alone could support a Category 5 storm, and it's up to atmospheric factors, such as wind shear or dry air nearby, to thwart that scenario.
• "Anytime the shear confounds intensity is just a lucky break," he told Axios. "The random chance of shear occurring is essentially the same, but it's keeping the lid on a more dangerous situation, which was made more dangerous by climate change."

Of note: Fourth, a little-known feature beyond the world of hurricane research is present in shallower waters closer to the the northeastern Gulf Coast.

• A plume of outflow from the Mississippi River, which as freshwater is lighter and milder than salty water in the Gulf, is sitting close to the surface in the northeastern Gulf, according to Karthik Balaguru, an atmospheric scientist at the Pacific Northwest National Laboratory.

• Having low salinity freshwater on top, and salty ocean water below promotes stability, and is resistant to mixing when exposed to hurricane-force winds and waves.
• "When a hurricane moves over fresh plume waters, the efficiency with which it mixes the ocean decreases and the warm [sea surface temperatures] are more persistent," Balaguru told Axios via email. "Hence, fresh plumes tend to strengthen storms."
• The forecast landfall location in Florida's Big Bend is also unusual, as no storm of this magnitude has made a direct hit where the Panhandle transitions to the Peninsula since 1896. Depending on the exact track and intensity, it may be unprecedented all the way back to the start of reliable records in 1851.

The intrigue: Fifth, the "I" storm has a curse of sorts. Every storm beginning with I since 2019 has made landfall in the U.S. as a deadly Hurricane (Ida, Irma, Ian).

• Storms beginning with the letter "I" outnumber others on the list of most-retired names under the World Meteorological Organization's naming convention, with the majority of them occurring since 2001.

The bottom line: Hurricane Idalia may become the 14th "I" storm to have its name retired, depending on the scope and scale of its impacts.

Go deeper:

Intensifying Idalia strengthens en route to Florida

Tropical Storm Idalia is a feared Gulf intensification scenario