As the devastating toll from Hurricane Michael becomes ever more clear, it has become apparent that it bears startling resemblance to yet another disastrous cyclone that struck the Sunshine State: Hurricane Andrew.
The “benchmark storm” for wind damage in the United States for the past 2½ decades, Andrew killed 65 people during its 1992 rampage. The storm rapidly intensified to a Category 5 before slamming suburbs just south of Miami on Aug. 24.
At hardly 300 miles across, Andrew was a relatively compact storm — but its lackluster size was dwarfed by its hellacious intensity. The storm destroyed much of Homestead, Fla., littering the landscape with the remnants of homes and businesses.
In its path was the National Hurricane Center, where meteorologists were busy tracking the storm. A 164 mph gust in the eyewall decimated the radar dome, transmitting one last eerie image to the forecasters’ monitors.
Many said that a windstorm like Andrew was a once-in-a-lifetime event. But there are indications that Michael struck with similar ferocity.
Like Andrew, Michael intensified rapidly right up through landfall. Andrew’s pressure dropped 19 millibars in the five hours before slamming into South Florida, strengthening from a Category 4 to a Category 5. Michael’s pressure dropped about 48 millibars in the 24 hours before landfall, strengthening from a Category 2 to a high-end 4.
What stood out the most from both storms wasn’t their rainfall. It was their unusually strong and concentrated wind field.
Michael’s wind wiped out forests as far as 15 miles inland like a giant lawn mower. Its eyewall, the zone of most extreme winds, in essence behaved like a high-end EF-3 tornado 30 miles wide.
A mere block or two outside the eyewall’s path, neighborhoods escaped virtually untouched.
Hurricanes are known for their wind. But typically their destructive gusts are concentrated along the immediate coastline. This was not at all the case with Andrew and Michael.
Tree and structural damage from Andrew and Michael extended uncharacteristically far inland and more closely resembled that of a tornado than a hurricane. That prompted the renowned severe storms researcher Tetsuya “Ted” Fujita to survey the damage after Andrew back in 1992. He found minuscule swaths of obliteration corresponding to instantaneous wind gusts within the 180-200 mph range. That led to his discovery of hurricane “miniswirls.”
They’re like tornadoes, but they form completely differently. As strong winds experience friction and are slowed down by objects near the ground, little eddies can form. The vicious winds just a few hundred feet up continue to howl unimpeded, forming a vacuum that can stretch this vortex upward. That strengthens the whirlwind, and before long a 70 to 80 mph tornado-like “miniswirl” is born.
That alone isn’t overly impressive, but added to an already forceful 120 mph hurricane circulation, the combined wind gust to 200 mph is simply staggering. Weather Channel meteorologist Mike Bettes was nearly swept off his feet by a miniswirl in Hurricane Irma last year.
Frictional effects imparted by the ground on major landfalling hurricanes can also result in long, tube-like vortices forming. The air near the ground is slowed, forming rotating horizontal rolls that can enhance damage in alternating stripes. In between, the winds slacken — but where the vortex tubes line up, the damage is even more extreme.
The circulations associated with miniswirls occur close enough to ground level that the radar beam overshoots them. Plus, they’re small enough that radar wouldn’t be able to detect them anyway. But National Weather Service Doppler radar did manage to pick up some horizontal vortex tubes lining up off Panama City, just like ripples forming in the wake of a stone in a river.
These tubes almost certainly overspread the eastern side of the eyewall near Mexico Beach, although the radar couldn’t “see” them since they were oriented parallel to the beam.
In any case, these oddities occur only in the strongest tropical cyclones.
Hurricane Andrew was initially classified as a high-end Category 4 when it made landfall in South Florida. Subsequent analysis of the available data prompted the National Hurricane Center to upgrade the intensity to Category 5. It’s possible that history could repeat itself with Michael after post-storm surveys are completed.