Early Tuesday morning, Tropical Storm Idalia strengthened into Hurricane Idalia, charting a course for Florida’s west coast and panhandle. Its maximum sustained winds have already reached nearly 100 miles per hour, and it’s expected to maintain feeding on exceptionally warm ocean waters and intensifying before making landfall early Wednesday.
It will pound Florida—including heavily populated Tampa Bay—with a trifecta of compounding hazards: high winds, pouring rains, and an enormous storm surge, which could reach as much as 15 feet. The National Hurricane Center expects that “life-threatening” surge to bring “catastrophic impacts.”
While most individuals understand that a hurricane brings wind and rain, the storm surge element is what causes extreme danger to coastal communities. That’s what happens when a storm becomes an enormous, swirling bulldozer that pushes a wall of water toward the shore. “The whole Gulf Coast of Florida—peninsula and panhandle—is one of the storm-surge-vulnerable areas of the United States, and even the world,” says Rick Knabb, a hurricane expert on the Weather Channel and former director of the National Hurricane Center. “The only method to make sure you survive a storm surge—especially a catastrophic storm surge, which is what we’re expecting within the Florida Big Bend and Apalachee Bay tomorrow morning—is to not be there when it happens.”
Any hurricane feeds on warm water: Warm, moist air rises off the ocean surface, sending energy into the atmosphere. That moisture condenses into clouds and thunderstorms and releases its latent heat, warming the core of the storm. That in turn lowers air pressure, which increases winds, which increases how much water the system can evaporate off the ocean.
Idalia has been feeding on soaring ocean temperatures. “It’s a machine that increasingly takes advantage of an increasing amount of warmth and moisture that it’s extracting from the ocean,” says Knabb. “Temperatures are way up into the 80s and near 90 degrees in lots of parts of the eastern Gulf of Mexico. The Gulf is all the time warm enough to support hurricanes, but this yr is way warmer than average, and in lots of locations at record levels.”
In general, climate change is dramatically warming the world’s oceans, providing fuel for extra-powerful hurricanes. But atmospheric dynamics are at play, too: Trade winds have been slow these days within the tropical Atlantic and across the Caribbean. Those winds would typically churn up deeper, cooler waters. But with less of that upwelling, the waters within the Caribbean and around Florida have been heating like a pot on slow boil. “All of that has been festering for weeks and weeks,” Knabb says. “And now those waters are getting used by this hurricane to fuel it.”
As Idalia chugs toward Florida, its winds are pushing a column of saltwater toward shore. The stronger the winds, the upper the water will probably be. The hurricane’s low pressure can also be making a kind of offshore dome of water centered under the storm. The water rises because there’s less atmospheric pressure on the ocean there. “That dome peaks right under the attention, where you’ve very low pressure,” says Brian McNoldy, a hurricane researcher on the University of Miami. “When the hurricane makes landfall, that dome of ocean water comes together with it.”
