Warm oceans strengthened Hurricane Francine and could power more Fall storms
Warm water in the Gulf of Mexico helped Hurricane Francine strengthening rapidlycreating danger for Louisiana residents who need to quickly stock up on supplies and secure their homes before the storm makes landfall on Wednesday.
Warm ocean water is essential for hurricane formation and strengthening. Heat helps evaporate water faster, feeding the storm and bringing more rain.
Mid-September is usually the peak of hurricane season and Francine moved through a part of the ocean that contained an exceptional amount of energy.
By Wednesday afternoon, Francine had strengthened to a Category 2 hurricane with sustained winds of nearly 100 mph (161 km/h).
Listen to the high water temperatures in the Gulf of Mexico that are affecting Francine and the hurricane season:
HOW WARM IS THE WATER?
The Gulf of Mexico doesn’t need record temperatures to form hurricanes this time of year. Still, Francine traveled through waters that were slightly warmer than average at the surface, but not record-breaking. The storm passed through an area that was about 86 to 88 degrees (30 to 31 degrees Celsius).
What is unusual is the amount of heat deeper. Storms churn up the ocean and bring cooler water to the surface.
Recently, however, that deeper layer has been record-breaking, trapping more heat than at any time in the past decade, said Brian McNoldy, a senior research associate at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science.
“The past week has been quite exceptional,” he said.
And Francine passed a stretch of water, called an eddy, that was particularly hot.
Closer to shore, however, the water is somewhat cooler than average, meaning there is less energy to power the storm.
“The window for real intensification has closed, so that’s good news,” he said.
HOW DID FRANCINE REACT?
Warmer water lower down in the seafloor is especially important for large, powerful, slow-moving storms. That’s the recipe for generating deeper water.
“On the other side of that, a weaker, smaller, faster-moving storm is not going to stir up the ocean much at all,” McNoldy said. For these storms, the temperature of deeper water is less important.
According to McNoldy, Francine is not extremely powerful, so the energy stored deeper in the Gulf of Mexico was less important.
Still, conditions were favorable enough for the storm to quickly intensify. On Tuesday afternoon, Tropical Storm Francine had sustained winds of 65 mph (105 km/h). A day later, it was nearing 100 mph (161 km/h). Such rapid changes can make storms more dangerous and faster, and can catch those in their path by surprise.
“Our model projections tell us that this is the kind of thing that is going to happen much more often as we go into the 21st century, as global warming continues to increase,” said Gabriel Vecchi, a hurricane researcher at Princeton University who also directs the High Meadows Environmental Institute.
But there are other factors that are reducing the strength of Hurricane Francine, said Bob Smerbeck, a senior meteorologist with AccuWeather. Dry air nearby has weakened its growth, and as the storm moves closer to shore, winds will distort the shape of the hurricane, further weakening its strength.
“Once it comes inland, it will weaken quickly, but it will cause a lot of damage along the way,” Smerbeck said.
WHAT ABOUT LONG-TERM TRENDS?
Federal meteorologists predicted an intense hurricane season. And a major storm came historically early. Hurricane Beryl formed in late June and Category 5 reached.
But by midseason, activity was fairly average, with just six named storms this Atlantic hurricane season. August was particularly quiet, according to Robert West, a hurricane and climate researcher at the University of Miami and affiliated with the National Oceanic Atmospheric Administration.
But the Atlantic coast is far from out of the danger zone.
“It seems like the tropics are waking up a little bit,” West said.
The high temperatures in the Gulf of Mexico will help and provide ample fuel.
Long-term trends are also at play. Climate change is warming oceans around the world, though experts say it’s hard to tie specific hurricane seasons or storms to a warming planet, West said.
And there are global weather patterns. Federal meteorologists said this summer that La Niña could develop. That’s where parts of the Pacific Ocean have cooler water surface temperatures. When that happens, it can reduce winds that weaken hurricanes.
“This could be the start of a busy period here,” Smerbeck said.
___
The Associated Press receives support for its water and environmental policy coverage from the Walton Family Foundation. The AP is solely responsible for all content. For all of AP’s environmental coverage, visit https://apnews.com/hub/climate-and-environment