»Why the rapid strength­en­ing of Hur­ri­cane Michael stunned the ex­perts,

The Atlanta Journal-Constitution - - FRONT PAGE - By David Fleshler Sun Sen­tinel

FORT LAUD­ERDALE, FLA. — As Hur­ri­cane Michael drew strength from the warm wa­ters of the Gulf of Mex­ico, it stunned ex­perts with its abrupt trans­for­ma­tion from gar­den-va­ri­ety Oc­to­ber storm to his­tory-mak­ing mon­ster.

At the Na­tional Hur­ri­cane Cen­ter, as the storm’s grow­ing power was be­com­ing clear, one fore­caster wrote that its rapid in­ten­si­fi­ca­tion in the face of un­fa­vor­able high-al­ti­tude winds “de­fies tra­di­tional logic.”

“You could tell they were flum­moxed,” Phil Klotzbach, re­search sci­en­tist in the De­part­ment of At­mo­spheric Science at Colorado State Uni­ver­sity, said. “This shouldn’t be hap­pen­ing, but it is.”

The storm’s sud­den in­ten­si­fi­ca­tion to near-Cat­e­gory 5 power, with winds of 155 mph when it slammed into Mex­ico Beach, un­der­lined the con­tin­ued lag in fore­cast­ers’ abil­ity to pre­dict a storm’s strength, even as they dis­play grow­ing vir­tu­os­ity in say­ing where it will make land­fall.

In the case of Michael, the storm ap­peared to be head­ing into a hur­ri­cane-snuff­ing en­vi­ron­ment of strong wind sheer, the dif­fer­ences in wind speed and di­rec­tion that can dis­rupt a hur­ri­cane’s ro­tat­ing, cone-shaped struc­ture. But these winds ap­peared to fade sooner than ex­pected, and the hur­ri­cane found it­self in a highly fa­vor­able en­vi­ron­ment, with a moist at­mos­phere and above-av­er­age wa­ter tem­per­a­tures. Gen­er­ally warm to be­gin with, the wa­ter of the Gulf of Mex­ico had a tem­per­a­ture of two or three de­grees higher than nor­mal.

“Once that sheer weak­ened, the rest of the con­di­tions were al­ready present,” said Corene J. Matyas, a hur­ri­cane ex­pert and as­so­ciate pro­fes­sor in the De­part­ment of Ge­og­ra­phy at the Uni­ver­sity of Flor­ida. “It had all the en­ergy it needed, so once those winds re­laxed, it was able to use that en­ergy to the fullest.”

The Na­tional Hur­ri­cane Cen­ter de­fines rapid in­ten­si­fi­ca­tion as a gain of at least 30 knots — or about 35 mph — in wind speed over a 24-hour pe­riod.

Such sud­den gains in power aren’t un­com­mon. Hur­ri­cane Pa­tri­cia, which struck Mex­ico’s Pa­cific coast on Oct. 23, 2015, strength­ened from trop­i­cal storm to Cat­e­gory 5 hur­ri­cane in 24 hours.

In Au­gust 2004, Hur­ri­cane Charley strength­ened from 110 mph to 150 mph in just a few hours be­fore strik­ing Flor­ida’s Gulf coast south of Sara­sota.

Fore­cast­ers to­day pre­dict a storm’s path with an ac­cu­racy that would have daz­zled their col­leagues of a gen­er­a­tion ago, but in­ten­sity fore­cast­ing, while im­proved, hasn’t shown the same gains.

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