By SETH BORENSTEIN AP Science Writer
A supersized El Niño’s decapitating winds and the Gulf of Mexico’s toasty, storm-fueling waters are battling over the future strength of Hurricane Isaias. And the storm’s tilt and eye show who’s winning.
All Atlantic hurricane season there has been “this battle between shear and just the overall conducive conditions,” said Colorado State University hurricane researcher Phil Klotzbach.
El Niño — the natural temporary warming of parts of the Pacific that warps weather worldwide — dominated. Its wind patterns smothered almost any wisp of a storm from strengthening in the Atlantic, while boosting what will soon be record high levels in the Pacific, Klotzbach said.
Wind shear versus warm waters
It’s called wind shear and it pushes the tops and middle of storms around, making them lopsided and keeping them from making a complete circular eyewall, which is when storms can really power up, Klotzbach and University at Albany’s Kristen Corbosiero said.
The other ingredients for a storm to turbocharge a storm are pushing back. There is plenty of fuel in warm water and moisture. The Gulf of Mexico is about 2.7 degrees (1.5 degrees Celsius) warmer than normal. The 86 degree waters (30 degrees Celsius) are 100 to 500 times more likely to be that extra hot because of climate change from the burning of coal, oil and gas, said climate scientist Kristina Dahl, vice president of the nonprofit Climate Central, which calculates the boost global warming causes to extreme weather.
“But there’s a certain point where it’s like, I don’t care how hot the waters are and how much moisture you have, if shear gets to a certain point, the shear is gonna win,” Klotzbach said.
The thunderstorm seeds of something bigger earlier in the week grew from circular winds over Central America but often were lopsided and couldn’t quite form a crucial eyewall, all because of El Niño’s high-level strong winds that pushed a would-be storm’s top sideways, experts said.
Then a window of moderation opened for just a couple of days, but it was enough, Corbosiero said. It makes sense it was in the Gulf of Mexico and in October, because El Niño has less of an effect in the Gulf than it does in the main Atlantic, she said. And storms often pop up in that region in October because of more northerly storm systems that help foster the right conditions.
Wind shear wasn’t exactly low, but it was a moderate level, when other factors like unusually warm waters and heavy moisture can kick in. Isaias rapidly intensified from 40 mph to 80 mph (64 kph to 129 kph) in a day and by late Wednesday, Isaias became the latest-in-the-season first Atlantic hurricane to form since 1914, Klotzbach said.
“The warm waters and high moisture won,” Klotzbach said. Isaias Friday was not tilting and had a strong eye, the hurricane center said.
By Friday morning, the storm was just below the threshold of being a major hurricane of 111 mph (178 kph) winds and was forecast to go as high as 120 mph winds before weakening to a strong Category 2 storm for landfall, according to the National Hurricane Center.
What to expect before landfall
Before Isaias comes ashore — forecast for probably somewhere from the Mississippi and Alabama coast to the Florida Panhandle late Friday night or early Saturday — the wind shear will strengthen from moderate levels of around 20 mph (32 kph) to 52 mph (84 kph) and then Isaias will start to struggle, which is good news for coastal residents, Klotzbach said.
But as of Friday morning, hurricane center forecasters said the coast is in “a tenuous spot” because it would only take a six-hour delay in the onset of that more intense wind shear for Isaias to bring a stronger-than-expected landfall. Regardless of what will happen with wind shear, it will still be a dangerous hurricane when it hits land, forecasters said.
“Once it gets to the coast, we know that the storm surge is going to be deeper and farther reaching because of sea level rise caused by climate change,” Dahl said. “So in this part of the world, there’s been about six and a half inches of sea level rise over the past 100 years or so that’s attributable directly to climate change.”
The National Hurricane Center is calling the surge “life-threatening.”
A warmer atmosphere means storms hold and then dump more rain, worsening flooding, Dahl said. The hurricane center is warning about urban, river and flash flooding in the Southeast this weekend.
“There’s a little bit of a battle here going on, but I think the really important thing to remember is that climate change is like this long-term big kahuna warming everywhere, and El Niño’s like a little icing on the cake,” Dahl said.
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