DENVER (AP) — A La Niña weather pattern combined warm humid air from the Gulf of Mexico, possibly irrigated by climate change, and decades of eastward shift of hurricanes to create the unusual early and deadly storm system that hit it. Alabama Thursday, meteorologists said.
And it could be the start of a bad hurricane year, an expert says.
Victor Gensini, a professor of meteorology at Northern Illinois University who studies hurricane patterns, said early signals that could change “show that the overall pattern is favorable for an above-average hurricane year.”
Gensini said his concern is mostly based on historical patterns and changes in atmospheric conditions that occurred when La Nina, a natural cooling of the Pacific that changed weather around the world, dissipated as predicted to happen in a few months.
A NECESSARY COMBINATION
For hurricanes to form, two major components are often needed that are not at high enough levels at the same time: wet storm instability and wind shear, which is the difference in wind speeds and directions at different altitudes.
“The cutoff is a guarantee” this time of year, said Harold Brooks, a senior scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “What if, when you get moisture you can have a (storm) system. That’s the stuff that’s usually missing at this time of year.”
Gensini said the cold front follows a classic fluctuation in jet stream (atmospheric rivers that move air systems) seen in La Nina winters. La Nina winters tend to produce more hurricanes, and NOAA this week said preliminary figures show 1,331 hurricanes in 2022, a La Nina year, 9% more than the average.
“If you’re going to get tornadoes in January, it’s this kind of setup that will produce them,” Gensini said.
Still, there’s no hurricane without moisture.
HOT HUMID AIR
Humidity measurements in Alabama air are about twice what they should be at this time of year, and more like May in Tornado Alley, an area that stretches from Texas to South Dakota and is known to be prone to hurricanes. That’s more than enough for a hurricane.
Hot humid air is coming from the Gulf of Mexico and “it’s a climate change signal,” he said.
Gensini pointed to NOAA measurements of water temperature in the Gulf on a computer screen and said: “Look at that number. 70 (21 degrees Celsius). 70. 70. This is ridiculous. That’s well above average for this time of year.” The warm water nearby squeezed the air.
“It’s the La Nina-type system you might expect, but it’s boosted by the abnormally warm Gulf of Mexico sea surface temperatures,” Gensini said.
Gensini said the warm moist air hits the cold front and rises like a ramp, and the hurricane-forming mix begins.
TORNADOS HIKE EAST
In the last few decades, a new pattern of hurricane activity has emerged.
According to a 2018 study by Gensini and Brooks, there are fewer tornadoes on Tornado Road and more east of the Mississippi River in the Southeast.
Hurricane activity is increasing the most in parts of Mississippi, Arkansas, Tennessee, Louisiana, Alabama, Kentucky, Missouri, Illinois, Indiana, Wisconsin, Iowa and Ohio, and Michigan. The biggest drop in tornado numbers is in Texas, but despite the decrease, Texas still receives the most tornadoes of any state.
Gensini said his lab is working this summer to try to figure out why.
MORE CHALLENGES
Brooks and Gensini said a nasty side effect of hurricanes moving east is that they move from less populated areas to more populated areas.
Brooks said that in Tornado Alley, a tornado can travel for miles and hit nothing and no one, so it wouldn’t be a problem. But in the East it is not so. People and buildings are on the way.
And people on the road are more vulnerable.
“There’s more poverty in the Southeast, there’s more mobile home population,” which is one of the most dangerous places to be in a hurricane, Brooks said.
Also, because of storm tracks or the routes that storms take due to wind and weather conditions, the more hurricanes hit to the east, the more likely they are to strike later in the day or even at night, when people are asleep or not heeding the warnings. Gensini said.
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