Why It Could Be The Worst Since Hurricane Katrina

Atlantic hurricane season starts on June 1, and the Gulf of Mexico is already warmer than average. Even more concerning is a current of warm tropical water that flows unusually far into the Gulf for this time of year, with the power to turn tropical storms into monster hurricanes.

It’s called the Loop Current, and it’s the 800-pound gorilla of the Gulf hurricane risks.

When the Loop Current moves so far north this early in the hurricane season — especially during what’s expected to be a busy season — it can be deadly for people along the northern Gulf Coast, from Texas to Florida.

If you look at temperature maps of the Gulf of Mexico, you can easily see the Loop Current. It meanders through the Yucatan Channel between Mexico and Cuba, into the Gulf of Mexico, then winds back through the Florida Straits south of Florida as the Florida Current, where it is the main contributor to the Gulf Stream.

The loop current was about as north as Tampa, Florida in mid-May 2022. The scale, in meters, indicates the maximum depth at which the temperature was 26°C or higher.Nick Shay/University of Miami

When a tropical storm moves across the loop current or one of its giant eddies — large rotating pools of warm water that flow off the current — the storm can explode in strength as it draws energy from the warm water.

This year, the Loop Current is remarkably similar to the way it did in 2005, the year Hurricane Katrina crossed the Loop Current before devastating New Orleans. Of the 27 storms listed that year, seven became major hurricanes. Wilma and Rita also crossed the Loop Current that year, becoming two of the most intense Atlantic hurricanes ever.

The Loop Current in May 2005 was strikingly similar to May 2022.Nick Shay/University of Miami

I have been tracking the heat content of the ocean for over 30 years as a marine scientist. The conditions I see in the Gulf in May 2022 are cause for concern. The National Oceanic and Atmospheric Administration is forecasting an above-average Atlantic hurricane season, with 14-21 named storms, six to 10 of which will be hurricanes. The loop current has the potential to charge up some of those storms.

Why the Loop Current Forecasters Worry

Warm ocean waters don’t necessarily mean more tropical storms. But once tropical storms reach waters around 26°C or warmer, they can amplify into hurricanes.

Hurricanes get most of their strength from the top 100 feet (30 meters) of the ocean. Normally, these upper ocean waters mix, allowing warm spots to cool quickly. But the Loop Current’s subtropical waters are deeper and warmer, as well as saltier, than the regular Gulf waters. These effects inhibit the mixing of the ocean and the cooling of the sea surface, allowing the warm current and its eddies to trap heat to great depths.

In mid-May 2022, satellite data showed that the Loop Current had water temperatures ranging from 78 F or warmer to about 100 meters. In the summer, that heat can extend to about 500 feet (about 150 meters).

The vortex that fueled Hurricane Ida in 2021 was over 86°F (30°C) at the surface and had heat up to about 590 feet (180 meters). With favorable atmospheric conditions, this deep heat reservoir helped the storm explode into a very powerful and dangerous Category 4 hurricane almost overnight.

Hurricane Ida’s pressure dropped rapidly as it crossed a warm, deep vortex boundary on August 29, 2021.Nick Shay/University of Miami

Within a storm, warm ocean water can create towering plumes of rising warm, moist air, fueling high-octane hurricanes. Think about what happens when you cook a large pot of spaghetti on the stove and how the steam rises as the water gets hotter. As more moisture and heat rise in a hurricane, the pressure drops. The horizontal pressure difference from the center of the storm to the periphery then causes the wind to accelerate, making the hurricane increasingly dangerous.

Because the loop current and its vortices have so much heat, they are not cooled significantly and the pressure will continue to drop. In 2005, Hurricane Wilma had the lowest central pressure ever in the Atlantic, and Rita and Katrina weren’t far behind.

How hurricanes get fuel from water.

La Niña, wind shear and other drivers of a busy season

Forecasters have other clues about how the hurricane season could be shaping up. One of these is La Niña, the climate opposite to El Niño.

During La Niña, stronger trade winds in the Pacific bring colder water to the surface, creating conditions that help push the jet stream further north. That tends to exacerbate the drought in the southern US and weaken wind shear there as well. Wind shear includes the change in wind speeds and wind directions with height. Too much wind shear can tear tropical storms apart. But less wind shear, courtesy of La Niña, and more moisture in the atmosphere could mean more hurricanes.

How La Niña affects us

La Niña was unusually strong in the spring of 2022, although it is possible that it will weaken later in the year, allowing for more wind shear towards the end of the season. For now, the upper atmosphere does little that would stop a hurricane from intensifying.

It’s too early to say what will happen to the steering winds that guide tropical storms and influence where they go. Even before then, conditions over West Africa are critical to whether or not tropical storms develop in the Atlantic. Dust from the Sahara and low humidity can both reduce the likelihood of storms.

Climate change has a role

As the temperature on Earth rises, the temperature of the ocean rises. Much of the heat retained by greenhouse gases released by human activities is stored in the oceans, where it can provide additional fuel for hurricanes.

Studies suggest the Atlantic is likely to see more storms progress to major hurricanes as those temperatures rise, although overall there won’t necessarily be more storms. A study examined the 2020 hurricane season — which had a record 30 named storms, 12 of which hit the U.S. — and found that the storms produced more rain than in a world without the effects of human-induced climate change.

Another trend we’ve noticed is that the Loop Current’s warm vortices have more heat than we saw 10 to 15 years ago. Whether that has to do with global warming is not yet clear, but the impact of a warming trend could be devastating.

This article was originally published on The Conversation by Nick Shay at the University of Miami† Read the original article here.

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