The Atlantic hurricane season begins on June 1, and the Gulf of Mexico is already warmer than average. Even more disturbing is a stream of hot 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 is called the loop current and is the 800 pound gorilla of hurricane hazards in the Gulf.
When the Loop Current reaches so far north so early in hurricane season – especially during a busy season – it can wreak havoc on people along the North Gulf Coast, from Texas to Florida.
If you look at the temperature maps of the Gulf of Mexico, you can easily locate the loop current. It winds through the Yucatan Canal between Mexico and Cuba in the Gulf of Mexico, and then hovers outward through the Florida Strait south of Florida to the Florida Stream, where it becomes the main contributor to the Gulf Stream.
When a tropical storm passes over a loop stream or one of its giant vortices – large swirling hot water lakes emitted by the stream – the storm can explode in force as it draws energy from the hot water.
This year, the loop current is strikingly similar to the way it did in 2005, the year that Hurricane Katrina crossed the loop before it devastated New Orleans. Of the 27 so-called storms that year, seven became major hurricanes. Wilma and Rita also crossed the Loop Current that year and became two of the strongest hurricanes in the Atlantic to be recorded.
I have been monitoring the heat content of the oceans for more than 30 years as a marine scientist. The conditions I see in the Gulf in May 2022 are a cause for concern. A significant forecast predicts 19 tropical storms – 32% more than average – and nine hurricanes. The loop current has the potential to overload some of these storms.
Why the loop current worries meteorologists
The warm water of the oceans does not necessarily mean more tropical storms. But once tropical storms reach waters that are about 78 F (26 C) or warmer, they can become hurricanes.
Hurricanes draw most of their strength from the top 100 feet (30 meters) of the ocean. Normally, these upper ocean waters are mixed, allowing hot spots to cool quickly. But the subtropical water of the Loop Current is deeper and warmer, and also saltier than the common water of the Gulf. These phenomena inhibit the mixing of the oceans and the cooling of the sea surface, allowing the hot stream and its vortices to retain heat at great depths.
In mid-May 2022, satellite data showed that the loop stream had water temperatures of 78 F or higher at about 330 feet (100 meters). By summer, this heat could have spread to about 500 feet (about 150 meters).
The vortex that triggered Hurricane Ida in 2021 was above 86 F (30 C) at the surface and had a heat of about 590 feet (180 meters). With favorable atmospheric conditions, this deep heat tank helped the storm to explode almost overnight in a very strong and dangerous Category 4 hurricane.
In a storm, warm ocean water can create towering clouds of warm, humid rising air, providing high-octane fuel for hurricanes. Think about what happens when you boil a large pot of spaghetti in the stove and how the steam rises as the water heats up. As humidity and heat rise in a hurricane, the pressure drops. The horizontal pressure difference from the center of the storm to its periphery then causes the wind to accelerate and the hurricane to become more and more dangerous.
As the loop current and its vortices have so much heat, they do not cool significantly and the pressure will continue to drop. In 2005, Hurricane Wilma had the lowest central pressure ever recorded in the Atlantic, and Rita and Katrina were not far behind.
La Niña, wind shear and other guides of a busy season
Meteorologists have other clues as to how the hurricane season could be shaped. One is La Niña, the climate opposite El Niño.
During La Niña, the strongest commercial winds in the Pacific Ocean bring colder water to the surface, creating conditions that help push the jet further north. This tends to worsen drought in the southern US and also weaken wind shear there. Wind shear involves changing the wind speed and wind directions with altitude. Excessive wind shear can dissipate tropical storms. But less wind shear, thanks to La Niña, and more humidity can mean more hurricanes.
La Niña was unusually strong in the spring of 2022, although it is likely to weaken later in the year, allowing for greater wind shear towards the end of the season. At the moment, the upper atmosphere does little to prevent a hurricane from intensifying.
It is too early to say what will happen to the winds that drive tropical storms and affect where they go. Even before then, conditions in West Africa are critical to whether tropical storms are forming in the Atlantic at all. Sahara dust and low humidity can reduce the chance of storms.
Climate change plays a role
As global temperatures rise, so does the temperature of the oceans. Much of the heat trapped by greenhouse gases released by human activities is stored in the oceans, where it can provide additional fuel for hurricanes.
Studies show that the Atlantic is likely to see more storms intensifying in large hurricanes as these temperatures rise, although there will not necessarily be more storms overall. One study looked at the 2020 hurricane season – which had a record 30 hurricanes, 12 of which hit the United States – and found that the storms produced more rain than they would in a world without the effects of climate change. caused by humans.
Another trend we have noticed is that Loop Current hot whirlpools have more heat than we saw 10 to 15 years ago. Whether this is related to global warming is not yet clear, but the impact of a warming trend can be devastating.