La Niña is here. That’s bad news for hurricane season and wildfires

Tropical systems whirl in the Atlantic and wildfires rage off the Pacific Coast. So this news comes at a bad time:

La Niña is back, the National Oceanic and Atmospheric Administration announced Thursday. And it could make life even harder for those living under the threat of Atlantic hurricanes and those threatened by the historically destructive western Wildfires.

La Niña is a recurring climate phenomenon in the Pacific Ocean that impacts weather conditions across the globe. In the Atlantic, that could mean two things, says Colorado State University research scientist and hurricane forecaster Philip Klotzbach:

More powerful storms could form because there will be no wind shear to weaken them as they cross the ocean, and they’ll continue to develop late into this hurricane season.

For the west coast, which is battling wildfires that have killed nearly two dozen, displaced thousands and burned millions of acres, La Niña means a drier winter and conditions more conducive to the start of even more fires, said Stanford University climate scientist Noah Diffenbaugh.

Satellite imagery of the Atlantic Ocean on Saturday, Sept. 12. The Atlantic currently has six tropical systems, two of which was tropical storms. [ National Oceanic and Atmospheric Administration ]

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La Niña — Spanish for “the little girl” — is a phenomenon where sea surface temperatures across the central and eastern Pacific Ocean are cooler than average, said Klotzbach, which in turn affects the Caribbean and Atlantic.

This year’s phenomenon is the first since 2017 — and it’s expected to last into at least February, according to government scientists with the atmospheric administration.

Klotzbach said La Niña contributes to an increase in hurricane activity — and the strength of those storms — by weakening wind shear over the Caribbean Sea and tropical Atlantic Basin. Without wind shear, storms are able to strengthen at will over warm ocean waters.

The phenomenon has the opposite effect of El Niño — Spanish for “the little boy” — which is when those Pacific waters are warmer than average, creating stronger wind shear in the Atlantic.

El Niño suppresses storm activity and effectively ended the 2015 storm season when it emerged, Klotzbach said.

It’s here! Today NOAA declared that #LaNina conditions are now present. Read more at @NWSCPC: https://t.co/1SoztfCqpc pic.twitter.com/XuYf0npd6Q
— National Weather Service (@NWS) September 10, 2020

Wind shear’s effect on a storm can be seen this weekend in the mid-Atlantic, Klotzbach said, where Tropical Storm Paulette has spent days struggling to strengthen because it is battling wind shear.

“When you have a bunch of wind shear, it’s bad for hurricanes,” Klotzbach said. “A classic case ... of this is Paulette. It’s being very strongly sheared. But that shear is essentially expected to drop from 40 mph to zero, and when it goes down, they’re expecting the storm to intensify really quickly.”

That’s why the hurricane center projects that Paulette will strengthen into a hurricane on Sunday morning and threaten Bermuda. It could develop into a “dangerous hurricane” Sunday night or Monday, according to the hurricane center.

What happens to Paulette could signal what the rest of this hurricane season will look like: Every storm that forms in the Atlantic now has a greater chance of strengthening, and there’s less wind shear to inhibit it.

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If that wasn’t bad enough, Klotzbach believes that La Niña will also mean hurricane season won’t ramp down in the fall as usual. Instead, there’s a greater chance that the Caribbean could produce powerful hurricanes late into the season, which officially ends Nov. 30.

“The reason why hurricane season ends when it does is (because) the shear gets too strong ...,” Klotzbach said. “Though the hurricane season usually goes to November, it’s usually pretty died down by then.

"In a La Niña year, we can sometimes get nasty storms into November.”

Thursday marked the annual climatological peak of hurricane season. There have already been 18 tropical storms, 5 hurricanes, and one major hurricane, Laura, which struck Louisiana and Texas in August. That is a record pace nearing the busiest season on record, 2005, which saw 27 named storms, 15 hurricanes and seven major ones.

While 2020 has yet to see that kind of storm development, the Atlantic has been active for weeks. There were three tropical storms — including Sally, which formed Saturday as it passed by Florida — two tropical disturbances and one depression in the Atlantic this weekend. That kind of storm development isn’t likely to let up.

“There’s plenty to keep us busy out there right now for the next two weeks,” Klotzbach said. “Once we get past these we can reassess and see what will be coming down the pipe in October.”