Hurricane season begins in the Atlantic Ocean on June 1, and the Gulf of Mexico is already warmer than average. Even more worrisome is a stream of warm tropical water that flows unusually far into the bay for this time of year, with the potential to turn tropical storms into brutal hurricanes.
It’s called the Loop Current, and it’s an 800 pound hurricane hazard of the Gulf.
When the Loop Current reaches far north early in the hurricane season—particularly during what is expected to be a busy season—it can spell disaster for people along the northern Gulf Coast, from Texas to Florida.
If you look at temperature maps for the Gulf of Mexico, you can easily spot the Loop Current. It’s chttps://bigthink.com/https://bigthink.com/https://bigthink.com/https://bigthink.com/https://bigthink.com/https://bigthink.com/https https://bigthink.com/https://bigthink.com/https://bigthink.com/https://bigthink.com/urls Through the Yucatan Channel between Mexico and Cuba, into the Gulf of Mexico, then swings across the Straits of Florida south of Florida In the name of the Florida Stream, it becomes the main contributor to the Gulf Stream.
When a tropical storm passes over the annulus current or one of its giant eddies—large, rotating pools of warm water spiking out from the current—the storm can erupt forcefully because it draws energy from the warm water.
This year, the Loop Current looks 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 identified that year, seven became major hurricanes. Wilma and Rita also crossed the Loop Current that year and became two of the deadliest Atlantic hurricanes on record.
I have been observing the ocean heat content for over 30 years as a marine scientist. The conditions I see in the Gulf in May 2022 are worrying. The National Oceanic and Atmospheric Administration predicts an above-average hurricane season in the Atlantic, with 14-21 named storms, six to 10 of which are hurricanes. The annular current has the potential to overcharge some of these storms.
Why does the Loop Current worry forecasters
Warmer ocean waters don’t necessarily mean more tropical storms. But once tropical storms reach waters of about 78 F (26 C) or warmer, they can strengthen into hurricanes.
Hurricanes derive most of their power from the top 100 feet (30 meters) of the ocean. Normally, this upper ocean water mixes, allowing the warm patches to cool quickly. But the subtropical waters of the Loop Current are also deeper, warmer, and saltier than the common Gulf waters. These effects prevent ocean mixing and cooling of the sea surface, allowing the warm current and its eddies to retain heat to great depths.
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In mid-May 2022, satellite data showed that the Loop Current had water temperatures of 78 F or warmer to about 330 feet (100 meters). By summer, this heat can extend to about 500 feet (about 150 metres).
The vortex that fueled Hurricane Ida in 2021 was over 86 F (30 C) at the surface and its temperature dropped to about 590 feet (180 meters). With favorable weather conditions, this deep reservoir of heat helped the storm explode almost overnight into a very powerful and dangerous Category 4 hurricane.
During a storm, warm ocean waters can create towering columns of warm, moist, billowing air, providing high-octane fuel for hurricanes. Think about what happens when you boil a large pot of spaghetti on the stove and how the steam rises as the water gets hotter. As the humidity and heat inside a cyclone rise, the pressure drops. The difference in horizontal pressure from the center of the storm to its periphery subsequently leads to an acceleration of the winds and an increase in the severity of the hurricane.
Because the loop current and its vortices have a lot of heat, they don’t cool down 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.
La Niña, wind shears and other drivers in the busy season
Forecasters have other clues about how hurricane season is shaping up. One is La Niña, the opposite climate to El Niño.
During La Niña, strong Pacific trade winds bring cold water to the surface, creating conditions that help push the jet stream far north. This exacerbates drought in the southern United States and weakens wind shear there. Wind shear involves the change in wind speed and wind directions with altitude. Too much wind shear can rip tropical storms apart. But less La Niña winds and increased atmospheric humidity could mean more hurricanes.
La Niña was unusually strong in the spring of 2022, although it will likely weaken later in the year, allowing for more wind shear at the end of the season. Right now, the upper atmosphere is doing little to stop a hurricane’s intensification.
It’s too soon to know what will happen with the guidance winds that direct tropical storms and affect where they’re headed. Even earlier, conditions in West Africa are crucial to whether tropical storms ever form in the Atlantic. Dust from the Sahara and low humidity can reduce the likelihood of storm formation.
Climate change has a role
As global temperatures rise, so does the temperature of the ocean. Much of the heat entrapped by greenhouse gases released by human activities is stored in the oceans, where they can provide additional fuel for hurricanes.
Studies show that the Atlantic is likely to see more storms that intensify into major hurricanes as these temperatures rise, although there won’t necessarily be more storms overall. The study examined the 2020 hurricane season — which recorded 30 named storms, 12 of which hit the United States — and found that storms produced more rain than would have occurred in a world without the effects of human-caused climate change.
Another trend we notice is that the warm eddies in the Loop Current have more heat than we saw 10 to 15 years ago. Whether this is related to global warming is not yet clear, but the effect of the warming trend could be devastating.
This article was updated on May 24, 2022, with the Atlantic hurricane season forecast from NOAA.
This article has been republished from The Conversation under a Creative Commons license. Read the original article.