Har­vey, Irma, Jose: ‘Mean sea­son’ has a rea­son

Na­ture, sci­ence and bad luck com­bined

USA TODAY International Edition - - FRONT PAGE - John Ba­con @jm­ba­con USA TO­DAY

First it was Har­vey. Then Irma. Now Jose lurks.

The hur­ri­cane sea­son has ar­rived with a deadly vengeance, and sci­ence can ex­plain a few rea­sons why.

“Every year around this time, even in quiet years, we get some ac­tive sys­tems,” Accu Weather me­te­o­rol­o­gist Evan Duf­fey said. “Hur­ri­cane sea­son has a pretty de­fined peak of late Septem­ber and early Oc­to­ber.

“That’s just the way it is.” Th­ese storms ar­rived a bit early, but not dras­ti­cally so, Duf­fey said. He also pro­vided some ideas to help ex­plain this mean sea­son, when two storms alone have killed dozens of Amer­i­cans and caused more than a quar­ter­tril­lion dol­lars in dam­age.

“We don’t like to get into the po­lit­i­cal de­bate (about cli­mate change),” Duf­fey said. “This year we have had some events that may have con­trib­uted to the sever­ity of the storms.”

Duf­fey said a drought in northwest Africa in re­cent years prob­a­bly played a role in the rel­a­tively quiet sea­sons of the re­cent past. The dust from the drought is picked up by weather sys­tems that roll west over the At­lantic. The dust tends to have a dry­ing ef­fect on de­vel­op­ing storms — “that leads to weak­en­ing,” he said.

This year the drought was sig­nif­i­cantly re­duced in Morocco and else­where, the dust waned ear­lier, and it wasn’t as heavy, Duf­fey said.

An­other fac­tor was El Niño, or the lack thereof. The weather phe­nom­e­non en­hances ver­ti­cal wind shear, which can sup­press hur­ri­cane ac­tiv­ity.

No dust from Africa to dry the storms, no winds from El Niño to chop them down. Na­ture and some bad luck did the rest. Hur­ri­cane Har­vey smashed into the south­east coast of Texas and south­west Louisiana, stalling and churn­ing out rain for days. Then came Irma, blast­ing straight up Flor­ida and wreak­ing havoc on both its coasts.

Jose is next. It’s smaller, weaker and not likely to make land­fall in the U.S. But its odd, loop­ing track has me­te­o­rol­o­gists watch­ing it closely. “If you live on the East Coast, don’t get too wor­ried,” Duf­fey said. “But pay at­ten­tion.”

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