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Hot water is the fuel for tropical cyclones like hurricanes and typhoons, and the weather this year has boosted the octane rating of the world’s oceans, forcing forecasters to revise their predictions upward.
Water temperatures in the Atlantic Ocean are at the highest levels since at least 1981, and some United States coastal waters, like those around Florida, recently reached hot tub levels of warmth: more than 100 degrees Fahrenheit.
Ordinarily, all this hot water would portend a season of intense tropical storms in the Atlantic, but there’s another unusual force tamping down on severe weather: An already-strong El Niño this year is roiling the Pacific Ocean. El Niño cycles on and off at intervals anywhere from two to seven years. Its knock-on effects reshape weather around the world, and over the Atlantic Ocean, El Niño tends to disrupt hurricane formation.
Back in May, the National Oceanic and Atmospheric Administration (NOAA) predicted that the combination of hot water and unstable air from El Niño would lead to a “near normal” hurricane season in the Atlantic, with 12 to 17 named storms and one to four major hurricanes.
But on August 10, NOAA decided that in the tug-of-war between hot water and rough air, the record high water temperatures were winning. The agency raised the likelihood of “an above-normal level of activity” for hurricanes this season. The forecast is now 14 to 21 named storms, with two to five turning into major hurricanes with winds above 111 miles per hour.
It’s an example of how forecasters are trying to expect the unexpected as air and water temperatures around the world are reach levels never before documented. There’s already been some unprecedented activity: Tropical storms Bret and Cindy around the Caribbean marked the first time two tropical storms formed in the month of June since record-keeping began in 1851. It’s a sign that the ocean was charged up with a lot of heat early in the season.
This year, NOAA scientists are also testing out a new system that could better predict one of the most dangerous aspects of hurricanes. While hurricane forecasting has seen huge improvements in recent years, the global climate is shifting into uncharted territory, so researchers have to continue to adapt in order to anticipate these storms and save lives.
What makes this year’s hurricane season so strange
A tropical cyclone — those giant spinning storms you can see from space — requires water temperatures to be at least 80 degrees Fahrenheit down to a depth of 150 feet. It begins as a tropical depression. When sustained winds top 39 miles per hour, it’s called a tropical storm, and when wind speeds reach 74 mph, it’s called a typhoon or hurricane. (In the Atlantic and the eastern Pacific oceans, these storms are called hurricanes; in the western Pacific, they’re called typhoons.)
While hot water is the key ingredient needed to brew a tropical storm, this year has introduced some other strong flavors.
“There is a relationship between sea surface temperature warming and potential intensity of tropical cyclones, but also there’s a number of other factors at play,” said Jane Baldwin, an assistant professor of earth system science at the University of California Irvine. “It doesn’t really work to just say, ‘Because temperatures are increasing, we’re going to see more storms or stronger storms.’”
The waters surrounding Florida are scorching hot. Experts are deploying numerous measures to protect, relocate, and “bank” live fragments of coral to help Florida’s Coral Reef survive a heat crisis that may last for months.https://t.co/1EGEKkLkvT pic.twitter.com/eIPtE60RFX
— NOAA Climate.gov (@NOAAClimate) July 28, 2023
A big factor to consider is not just the sea surface temperature but the temperature gradient between different parts of the ocean. And then we have to consider the air above the water.
One of the effects of El Niño is that it introduces more wind shear above the Atlantic. Between 5,000 feet and 35,000 feet above the ocean, the wind can drastically change direction and speed. These sudden wind shifts can rip up nascent tropical storms or extinguish them before they even form in the first place.
El Niño tends to have the opposite effect over the Pacific. The water in this ocean is also much warmer than normal, but the air is more stable than over the Atlantic. In El Niño years, the central and eastern Pacific tend to see more active hurricanes. Earlier this month, Tropical Storm Calvin passed just south of Hawaii.
Scientists have a new way to stay ahead of one of the most dangerous aspects of hurricanes
Last September, Hurricane Ian hit Florida’s Gulf Coast at Category 4 strength, with 155 mph sustained winds, driving a storm surge as high as 18 feet. Deaths from disasters in general have been declining around the world for nearly a century, but Ian defied that trend and killed at least 149 people. It was the deadliest storm to hit the mainland US since Katrina in 2005 and the deadliest in Florida since 1935.
A big part of why Hurricane Ian was so dangerous was that it was so hard to predict. These days, forecasters can map an accurate path of a hurricane 72 hours ahead or more, buying valuable time to evacuate, compared to 20 years ago, when such predictions could only come out 24 hours ahead of the storm. But Ian followed a less-traveled route for hurricanes that was harder to model, and small deflections in its path led to bigger swings in where it would make landfall. Local officials waited too long to order evacuations because they thought that early forecasts showed that their counties were outside the most dangerous region of the storm.
Another force behind Hurricane Ian’s destruction was that it underwent rapid intensification. That’s when a hurricane gains more than 35 mph in wind speed over 24 hours. The sudden speedup can turn a threatening storm into a monster, leaving little time for people to get out of the way. Ian actually rapidly intensified twice during its rampage.
“You can go from a tropical storm at night to a hurricane in the morning,” said Sundararaman Gopalakrishnan, who leads NOAA’s hurricane modeling team.
As average temperatures rise, some scientists expect that the conditions for rapid intensification will become more common.
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Forecasters are starting to get their hands around this phenomenon. This year, NOAA is trying out the Hurricane Analysis and Forecast System, which could anticipate hurricane tracks as far as seven days out and provide more useful predictions about rapid intensification. Gopalakrishnan said this model was a huge feat. NOAA has been working on this for decades, teaming up across its various offices and with outside partners to gradually improve their predictions.
The tricky thing is that it’s really hard to see inside a major storm like a typhoon. Satellite images only zoom in so far, so scientists often look into the storms themselves. That can require flying manned aircraft into hurricanes, but as of late, NOAA has been using more autonomous vehicles that can fly and float. That has given scientists a better read of the mechanism that leads hurricanes to spool up quickly.
“We’ve reached a point where we are starting to understand how storms undergo rapid intensification,” Gopalakrishnan said. The HAFS model creates what he described as a “telescoping nest” that lets scientists zoom into particular parts of the storm to see its boundaries and how its intensity is changing. The goal though is to make sure the forecasts are useful for people so they can plan to protect themselves and their property, and that means first figuring out where cyclones will land. And while HAFS also improves storm track forecasts, it’s not perfect, and making these projections better is still a high priority. “It’s location, location, location,” Gopalakrishnan said.
All the while, the planet’s climate is continuing to change, amplifying many of the destructive elements of storms like rainfall and storm surge. Even as predictions get better, researchers warn there may be more surprises in store.
Update, August 10, 2:25 pm ET: This story, originally published on August 2, has been updated with the news that NOAA revised its hurricane forecast.
