Break­ing down Hur­ri­cane Irma’s wind, wa­ter by the num­bers

Richmond Times-Dispatch Weekend - - Metro - BY JOHN BOYER Rich­mond Times-Dis­patch

Hur­ri­cane Irma’s stag­ger­ing strength led to cat­a­strophic loss on the Lee­ward Is­lands and mas­sive dis­rup­tion along the length of Florida.

Here is a pre­lim­i­nary run­down of the no­table weather ob­ser­va­tions and records from the storm. In­ten­sity

The peak sus­tained wind speeds in Hur­ri­cane Irma were mea­sured at 185 mph as the storm crossed the Lee­ward Is­lands, though mo­men­tary gusts around the eye likely ex­ceeded 225 mph.

That tied Irma with the 1935 Florida Keys hur­ri­cane, Gil­bert in 1988 and Wilma in 2005.

The record for high­est sus­tained winds in an At­lantic hur­ri­cane was set in 1980 by Hur­ri­cane Allen, which reached 190 mph.

Of the 422 hur­ri­canes in the At­lantic, Gulf of Mex­ico and Caribbean since 1950, only one had higher ob­served winds than Irma.

Irma’s pres­sure sank to a min­i­mum of 914 mil­libars on Sept. 6, which is tied for the 10th low­est for an At­lantic hur­ri­cane since 1950.

Irma main­tained that peak 185 mph wind speed longer than any other trop­i­cal cy­clone on record world­wide, but records in the Pa­cific and In­dian Oceans are very in­com­plete prior to the 1980s.

Oth­er­wise, Irma did not set records for longevity — it ex­isted as a named storm for nearly 13 days and spent 11 days as a hur­ri­cane. Land­fall

The eye of Hur­ri­cane Irma crossed over Bar­buda, Saint Martin and the Bri­tish Vir­gin Is­lands at Cat­e­gory 5 strength on Sept. 6, which made it the strong­est ever known to hit the Lee­ward Is­lands.

Irma be­came the first At­lantic hur­ri­cane to strike any land at Cat­e­gory 5 strength since Hur­ri­cane Felix hit Nicaragua in 2007.

Early on Sept. 9, Irma be­came the first hur­ri­cane to hit Cuba as a Cat­e­gory 5 since 1924.

Irma then turned north on Sept. 10 and crossed the Florida Keys at Cat­e­gory 4 strength with 130 mph sus­tained winds.

Irma weak­ened to a Cat­e­gory 3 with 115 mph sus­tained winds just be­fore mak­ing the se­cond and fi­nal land­fall in south­west Florida. The high­est gust in Florida was mea­sured at 142 mph in Naples.

It was Florida’s first ma­jor hur­ri­cane strike since Wilma in Oc­to­ber 2005, which co­in­ci­den­tally made land­fall in ex­actly the same spot.

Irma was the strong­est hur­ri­cane to hit Florida since Hur­ri­cane Charley in Au­gust 2004.

Storm surge

Storm surge varies greatly along the coast­line, and real-time mea­sure­ments from these tide gauges are few and far be­tween.

Coastal in­un­da­tion ex­ceeded 4 feet near Charleston, S.C.; Naples, Fla.; and Sa­van­nah, Ga. The St. Johns River near Jack­sonville set a new record by climbing to 5.26 feet above the typ­i­cal daily high tide level.

It’s likely that the surge was higher in the Florida Keys, but the of­fi­cial assess­ment is on­go­ing. Rain­fall

Florida ex­pe­ri­enced Irma’s heav­i­est rain­fall, with as much as 15.91 inches mea­sured in Fort Pierce.

Lo­cal­ized flood­ing oc­curred as far north as metro At­lanta and western North Carolina.

The storm broad­ened and weak­ened sig­nif­i­cantly af­ter cross­ing onto land, but some show­ers got as far in­land as the Ozarks, Great Lakes and Mid-At­lantic.

Irma did not threaten Vir­ginia with flood­ing be­cause the core of the storm came ashore too far away, and there was no front to stall and con­cen­trate the storm’s mois­ture into a zone of ex­ces­sive rain rates.

Hur­ri­cane Irma spawned at least 12 tor­na­does when it struck Florida, but the num­ber of re­ports may change as dam­age as­sess­ments con­tinue.

NOAA

A satel­lite im­age shows Hur­ri­cane Irma on Sept. 6.

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