How Michael grew into a 155 mph mon­ster

The Denver Post - - NEWS - By Seth Borenstein

WASH­ING­TON» Moist air, warm wa­ters in the Gulf of Mex­ico and ideal wind pat­terns su­per­charged Hur­ri­cane Michael in the hours be­fore it smacked Florida’s Pan­han­dle.

Hur­ri­cane Michael was barely a hur­ri­cane Tues­day morn­ing, with winds of 90 mph. A lit­tle over a day later, it had trans­formed into a mon­ster. When it made land­fall Wed­nes­day af­ter­noon, it was blow­ing at 155 mph. That’s a 72 per­cent in­crease in wind speed in less than 33 hours.

“Michael saw our worst fears re­al­ized, of rapid in­ten­si­fi­ca­tion just be­fore land­fall on a part of a coast­line that has never ex­pe­ri­enced a Cat­e­gory 4 hur­ri­cane,” Univer­sity of Mi­ami hur­ri­cane re­searcher Brian Mc­Noldy said Wed­nes­day morn­ing.

Hur­ri­canes have some­thing called a po­ten­tial in­ten­sity. That’s how strong a storm can get if all other fac­tors are aligned, said Na­tional Oceanic and At­mo­spheric Ad­min­is­tra­tion cli­mate and hur­ri­cane ex­pert Jim Kossin said. Michael had noth­ing hold­ing it back.

“Ev­ery­thing was there for it to reach its po­ten­tial, and it did,” Kossin said.

As Michael’s eye started com­ing ashore, it boasted the third­low­est cen­tral pres­sure of any storm to hit the United States, be­hind only a 1935 La­bor Day storm and 1969’s Camille.

Me­te­o­rol­o­gists first got a sense some­thing big could be hap­pen­ing by watch­ing how Michael’s eye changed shape. Early on Tues­day, it was oddly shaped and ragged. Later in the morn­ing, it started to get bet­ter or­ga­nized. By Tues­day night, real­time satel­lite im­agery was show­ing the eye get­ting stronger and scarier by the minute.

An­other fac­tor: its pres­sure, the mea­sure­ment me­te­o­rol­o­gists use to gauge a hur­ri­cane’s strength. The lower the pres­sure, the stronger the storm. Be­fore land­fall, Michael’s pres­sure fell so low, it looked like the winds were sure to pick up fast, said Ryan Maue, a me­te­o­rol­o­gist for weath­er­mod­els.com.

And none of the fac­tors that hold a storm back were present, es­pe­cially some­thing called “wind shear.” Wind shear is when there’s a mis­match ei­ther in speed or di­rec­tion be­tween winds near the sur­face and those five to six miles up.

That mis­match “pushes the storm over” or de­cap­i­tates it, Kossin said. When the wind shear near Michael eased, the storm took off, he said.

“It’s kind of like some­one was hold­ing on to it when it was try­ing to run, and they let it go,” Kossin said.

An­other huge fac­tor was the wa­ter tem­per­a­ture. Warm wa­ter is the en­ergy that fu­els hur­ri­canes, and the gulf wa­ter is 4 to 5 de­grees warmer than nor­mal.

Wa­ter tem­per­a­tures in the Gulf of Mex­ico vary along with weather, but some sci­en­tists said the warm wa­ters are signs of hu­man­caused cli­mate change.

“Have hu­mans con­trib­uted to how danger­ous Michael is?” Kossin said. “Now we can look at how warm the wa­ters are, and that cer­tainly has con­trib­uted to how in­tense Michael is and its in­ten­si­fi­ca­tion.”

The warm wa­ters, Kossin said, are a “hu­man fin­ger­print” of cli­mate change.

Kossin and oth­ers have a study out this month in the Jour­nal of Cli­mate with com­puter sim­u­la­tions show­ing that hu­man­caused global warm­ing will in­crease rapid in­ten­si­fi­ca­tion of trop­i­cal weather across the globe in the fu­ture.

Other stud­ies have shown rapid in­ten­si­fi­ca­tion has al­ready in­creased over past decades. One study this year in Geo­phys­i­cal Re­search Let­ters found that since 1986, the rate of in­ten­si­fi­ca­tion of storms such as Michael has in­creased by about 13 mph.

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