Hurricane Michael is looking even more violent on closer scrutiny

Gage Wilson and David Segal, technicians for the U.S. Geological Survey, were roaming the obliterated city of Mexico Beach when they spotted the missing sensor.

It was a barometer that USGS employees had deployed in advance of Hurricane Michael, a pressure gauge housed inside a two-inch-diameter aluminum tube. The employees had noted the specific spot where it was to measure the storm: "Barometer located on second light post from Highway 98 in pier parking lot."

But there was no more light post after Michael destroyed just about everything here with a massive storm surge and intense winds when it made landfall Oct. 10.

The USGS desperately needed that sensor to make an accurate estimate of the storm surge that barreled through Mexico Beach. Eleven days after Michael hit, demolishing most buildings in this seaside town, Wilson and Segal found the shiny cylinder, propped up vertically in front of the splintered ruins of a house as if hoping someone would find it.

Using data from that instrument and another sensor that had been nailed to a pier piling, the USGS on Thursday concluded the storm surge at Mexico Beach had reached 15.55 feet, half a foot higher than the previous estimate. If you add the waves on top of the surge, the water level here reached 20.6 feet, or close to the height of a two-story building.

That's what people in the hurricane business call "The Big One." The term has nothing to do with physical scale - Michael was average-sized. But it was unusually violent, among the four most-intense hurricanes to hit the mainland United States since records began in 1851.

"It might be the severest hurricane to hit the U.S. for as long as I'm still alive," said storm chaser Josh Morgerman, 48, who has been in 45 tropical cyclones and survived the eye of Michael in a disintegrating Holiday Inn Express in Callaway, Florida, an eastern suburb of Panama City.

Mike Brennan, chief of the hurricane specialist unit at the National Hurricane Center, said Hurricane Michael was violent in two really different ways.

"You had the violence of the winds, the Category 4 winds in the eyewall there, but then you had the violent storm surge that was obviously powerful enough to wipe buildings off their foundation," Brennan said.

The unlucky people of Mexico Beach suffered both the maximum winds and the maximum storm surge - the rise in ocean water above normally dry land that the storm plows ashore. In this violent zone, propped against the storm's calm eye, the forward speed of the hurricane adds to the speed of its counterclockwise circulation. The overlap maximizes the surge.

In a storm as intense as Michael, the eyewall's winds are equivalent to an EF3 tornado, strong enough to destroy solidly constructed homes and lift cars off the ground. The extreme wind damage in Panama City, on the left side of the eyewall, raises the possibility that Michael generated hurricane "mini-swirls," which are like tiny tornadoes, roughly the diameter of a couple of houses, and can create momentary wind speeds in excess of 200 mph.

Government scientists are still trying to take the measure of the historic storm. Though Michael was officially a Category 4 hurricane, with 155 mph sustained winds when it made landfall, that could potentially be revised upward, to Category 5 - 157 mph and higher - in the ongoing National Hurricane Center analysis.