The following essay is reprinted with permission from The Conversation, an online publication covering the latest research.
The Atlantic hurricane season begins on June 1. The Gulf of Mexico is already warmer that the average .. A current of warm tropical waters is flowing unusually deep into the Gulf at this time of the year. This could make tropical storms into monster hurricanes.
It’s called the Loop Current, and it’s the 800-pound gorilla of Gulf hurricane risks.
When the Loop Current reaches this far north during hurricane season, especially during what’s expected to be a busy period, it can spell disaster 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 spot the Loop Current. It travels through the Yucatan Channel, between Mexico and Cuba, into Gulf of Mexico. Then it swings south through the Florida Strait, becoming the Florida Current.
A tropical storm that passes over the Loop Current, or one of its giants eddies (large rotating pools of warm waters that spin off from it) can cause the storm to explode in strength. It draws energy from the warm waters.
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 named storms that year, seven became major hurricanes. Wilma and Rita also crossed the Loop Current that year and became two of the most intense Atlantic hurricanes on record.
I have been monitoring ocean heat content for more than 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 them hurricanes. Some of these storms could be supercharged by the Loop Current.
Why the Loop Current worries forecasters
Warm ocean water does not necessarily mean more tropical hurricanes. But once tropical storms reach waters that are around 78 F (26 C) or warmer, they can strengthen into hurricanes.
Hurricanes draw most of their strength from the top 100 feet (30 meters) of the ocean. These upper ocean waters mix normally, allowing warm areas to cool down quickly. The Loop Current’s subtropical water, which is deeper and warmer than the Gulf common water, is also saltier. These effects prevent ocean mixing and sea surface cool, allowing the warm current to retain heat to great depths.
In mid-May 2022, satellite data showed the Loop Current had water temperatures 78 F or warmer down to about 330 feet (100 meters). By summer, that heat could extend down to around 500 feet (about 150 meters).
The eddy that fueled Hurricane Ida in 2021 was over 86 F (30 C) at the surface and had heat down to about 590 feet (180 meters). This deep reservoir of heat enabled the storm to explode almost instantly into a dangerous Category 4 hurricane with favorable atmospheric conditions.
Warm ocean water can cause plumes of rising warm, moist, air to rise in storms, which can provide high-octane fuel to hurricanes. Think about what happens to large pots of spaghetti when they are heated on the stove. The steam rises as the water heats up. Pressure drops as more heat and moisture rise in a hurricane. The horizontal pressure difference between the center and its periphery causes the wind to pick up and makes the hurricane more dangerous.
The Loop Current and its eddies are so hot that they don’t cool down, and the pressure will continue falling. In 2005, Hurricane Wilma had the lowest central pressure on record in the Atlantic, and Rita and Katrina weren’t far behind.
La Nina, wind shear and other drivers of a busy season
Forecasters also have clues as to how the hurricane season might unfold. One is La Nina, which is the climate opposite to El Nino.
During La Nina, stronger trade winds in the Pacific Ocean bring colder water to the surface, creating conditions that help push the jet stream farther north. That tends to exacerbate drought in the southern U.S. and also weaken wind shear there. Wind shear refers to the variation in wind speeds and wind directions as a function of height. Too much wind shear can cause tropical storms to become disorganized. La Nina’s less wind shear and more moisture can lead to more hurricanes.
La Nina has been unusually strong in spring 2022, though it’s possible that it could weaken later in the year, allowing more wind shear toward the end of the season. The upper atmosphere is not doing much to stop a hurricane intensifying at the moment.
It is too early to predict what will happen to the steering winds that direct tropical storms and influence where they go. The conditions in West Africa will determine whether or not tropical storms develop in the Atlantic. Dust from the Sahara and low humidity can both reduce the likelihood storms will form.
Climate change has a role
As global temperatures rise, the ocean’s temperature is increasing. Much of the heat trapped by greenhouse gases that are released by human activities is stored in the oceans, where it can provide additional fuel for hurricanes.
Studies suggest that the Atlantic is likely to see more storms intensify into major hurricanes as those temperatures rise, though there won’t necessarily be more storms overall. A study examined the 2020 hurricane season – which had a record 30 named storms, 12 of them hitting the U.S. – and found the storms produced more rain than they would have in a world without the effects of human-caused climate change.
Another trend we have been noticing is that the Loop Current’s warm eddies have more heat than we saw 10 to 15 years ago. Although it’s not clear if this is related to global warming, the potential impact of a warming trend could prove devastating.
This article was originally published on The Conversation. Rea