By David Fleshler
Sun Sentinel
FORT LAUDERDALE, Fla. — As Hurricane Michael drew strength from the warm waters of the Gulf of Mexico, it stunned experts with its abrupt transformation from garden-variety October storm to history-making monster.
At the National Hurricane Center, as the storm’s growing power was becoming clear, one forecaster wrote that its rapid intensification in the face of unfavorable high-altitude winds “defies traditional logic.”
“You could tell they were flummoxed,” Phil Klotzbach, research scientist in the Department of Atmospheric Science at Colorado State University, said Thursday. “This shouldn’t be happening, but it is.”
The storm’s sudden intensification to near-Category 5 power, with winds of 155 mph when it slammed into Mexico Beach, underlined the continued lag in forecasters’ ability to predict a storm’s strength, even as they display growing virtuosity in saying where it will make landfall.
In the case of Michael, the storm appeared to be heading into a hurricane-snuffing environment of strong wind sheer, the differences in wind speed and direction that can disrupt a hurricane’s rotating, cone-shaped structure. But these winds appeared to fade sooner than expected, and the hurricane found itself in a highly favorable environment, with a moist atmosphere and above-average water temperatures. Generally warm to begin with, the water of the Gulf of Mexico had a temperature of two or three degrees higher than normal.
“Once that sheer weakened, the rest of the conditions were already present,” said Corene J. Matyas, a hurricane expert and associate professor in the Department of Geography at the University of Florida. “It had all the energy it needed, so once those winds relaxed, it was able to use that energy to the fullest.”
The National Hurricane Center defines rapid intensification as a gain of at least 30 knots —or about 35 mph — in wind speed over a 24-hour period.
Such sudden gains in power aren’t uncommon. Hurricane Patricia, which struck Mexico’s Pacific coast on Oct. 23, 2015, strengthened from tropical storm to Category 5 hurricane in 24 hours. In August 2004, Hurricane Charley strengthened from 110 mph to 150 mph in just a few hours before striking Florida’s Gulf coast south of Sarasota.
Although Floridians remember Hurricane Wilma for raking the state from west to east in October 2005, it’s famous among meteorologists for its explosive gain of strength over the western Caribbean, shooting from tropical storm to strong Category 5 hurricane, with 185 mph winds, in two days.
Hurricane Michael underwent three periods of rapid intensification, said Haiyan Jiang, associate professor of meteorology at Florida International University. Beginning Sunday, it strengthened from tropical depression to Category 1 hurricane, gained power and, within one 24-hour period, increased its maximum wind speed from 74 mph, or a minimal Category 1 hurricane, to 155 mph, a strong Category 4.
Forecasters today predict a storm’s path with an accuracy that would have dazzled their colleagues of a generation ago, having narrowed and lengthened the famous “cone of uncertainty” to reflect their ability to forecast a storm’s track five days in advance.
But intensity forecasting, while improved, hasn’t shown the same gains. While forecasting a storm’s path requires broad information on large-scale factors around a storm, such as winds and air pressure, forecasts of intensity require detailed, specific data from the most violent part of a hurricane’s interior, not the easiest place to do science.
“We try to fly through the storms as much as we can,” said Matyas, of the University of Florida. “They make passes and they drop instruments, but sometimes you don’t drop it where the strongest winds are going to go. You have to hunt around to find the exact spots where the strongest winds are blowing, and then drop your instruments in, remembering that you’re dropping it from let’s say 10,000 feet, it’s going to get blown sideways as it drops toward the ground. So it’s very, very difficult to measure.”
