It was startling, and frightening to Florida residents facing the landfall of Hurricane Ian last week. In less than 24 hours, the hurricane intensified from a mid-range category 3 storm to just shy of a catastrophic category 5, as it became the fifth-strongest storm on record ever to hit the continental United States.
It’s called “rapid intensification” and it’s happening with increasing frequency in the last hours before storms make landfall. Climate scientists explain that it’s a clear sign of the impacts of a warming globe.
The science is straightforward. Tropical storms form and get stronger over warm ocean waters. The heat causes air to rise, and the dropping air pressure at ocean level begins to create the distinctive clockwork spin of the storm. The warmer the water, the stronger and more devastating its winds become.
The central change producing more cases of rapid intensification is that the tropical ocean waters are getting warmer. That effect is magnified in shallower waters like the Gulf of Mexico, where there is less water below the surface to buffer the heat buildup. The Caribbean/Gulf waters over which Ian traveled were about 1.8 degrees warmer than the measured historical norm. That “turbocharged” the storm rapidly into the catastrophic category.
The rapid intensification effect is especially dangerous because it is occurring in the final period before landfall, giving the public shorter notice of the storm’s danger level. People who live in areas used to tropical storms often decline to evacuate unless and until they believe the risk level is higher than they are used to facing.
In a related note, storms are also now tending to dump more water in the form of rainfall, faster than usual. That’s an effect of the warmer atmosphere holding more evaporated moisture. The increased rainfall in a short time period heightens the flooding produced by the storm. Hurricane Ian is estimated to have dumped about 10% more rain as a result of climate change already experienced.
Climate change: producing stronger storms faster with more wind destruction and deadly flooding, with less warning. The longer it takes us to bring climate change under control, the worse it will get.