TAMPA, Fla. -- Small 'mini-swirl' winds packing punches of 200 mph explain why Hurricane Andrew leveled some houses while neighboring homes remained standing, an international wind expert says.
Ted Fujita, professor emeritus at the University of Chicago, spoke Wednesday at the Seventh Annual Governor's Hurricane Conference in Tampa. Fujita said the newly discovered superwinds probably accounted for only a small portion of the 35,000 homes that were destroyed by the hurricane in south Dade County Aug. 24. The storm caused $16.5 billion in insured losses in the county.
Fujita said the superwinds were small, about the size of two house lots.
'If you happen to live in a mini-swirl area, your house will be gone,' he said.
Using aerial photographs, videos and the pattern of fallen debris, Fujita said over the past couple of months he found evidence of at least 20 mini-swirls and said he estimates the hurricane created at least 100 of them.
Fujita, who developed the theory of downbursts that explained several deadly airline crashes and who created a scale for determining tornado intensity, said his study of Andrew and Hurricane Iniki that hit Hawaii showed evidence in the storm eyewalls of mini-swirls and another phenomenon: microbursts.
He said mini-swirls started as normal 10 to 20 mph swirling winds, but high clouds in the eyewall edge pulled the swirling winds upward. They contracted and spun faster, eventually hitting 80 mph. Added to the storm's existing 120 mph winds, the resulting combination hit with 200 mph winds, he said.
He said the superwinds lasted perhaps two-tenths to three-tenths of a second, as opposed to gusts that lasted about 30 seconds.
The mini-swirls were 50 to 200 feet in diameter, about one-thousandth of the width of Andrew.
Fujita said the mini-swirls are different from tornadoes because they are smaller, slower and vanish in an instant.
Jerry Jarrell, deputy director of the National Hurricane Center in Coral Gables, Fla., said there were no confirmed tornadoes in south Dade County during Andrew, though there were many as the hurricane crossed Louisiana.
Fujita said microbursts are weaker than mini-swirls. He said microbursts have winds of 160 mph and are smaller, about the size of a mobile home. He said microbursts are sudden, intense downward pushes of dry air from clouds.
Fujita said he never expected microbursts in a hurricane, because microbursts require dry air, but he said there was dry air near the eyes of the storms. He said he found about 20 microbursts where Iniki hit in Hawaii and two in Homestead in south Dade County.
Earlier, Bob Sheets, director of the National Hurricane Center, said Andrew's highest sustained winds were about 140 mph gusting to 175 mph. A University of Miami study also found sustained winds of 120 to 140 mph with peak gusts to 175 mph.