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Science of predicting intensity still uncertain

As Hurricane Andrew slammed South Florida on Aug. 24, 1992, forecasters said it packed winds of up to 145 mph.

On the storm's 10th anniversary, they changed their minds. Andrew was upgraded to a Category 5 storm with sustained winds of 165 mph.

Among the lessons that Andrew taught is that forecasting the intensity of complex tropical systems has always been an elusive challenge and remains so today, 20 years after one of history's most destructive storms.

"Although great advances in the track forecast have been made, the intensity forecast hasn't gotten much better," said William M. Gray, a hurricane researcher at Colorado State University. "That's a real bottleneck. We've known we've had the problem for years. These storms are so complex."

Storm structures vary tremendously and numerous factors contribute to their intensity.

"People who study these storms say each storm has its own personality,'' Gray said. "There's not one exactly like the other."

Bay News 9 meteorologist Mike Clay agreed: "Hurricane Andrew showed meteorologists that we really aren't good at predicting rapidly intensifying hurricanes."

Forecasting intensity has been the subject of much research over the past decade, but the science is still very much uncertain.

Meteorologists have improved at measuring wind speed.

Andrew was upgraded to Category 5 storm in part because of data captured from a dropsonde, a device dropped from hurricane reconnaissance aircraft into the eye wall, measuring a variety of factors every 15 feet on its way down.

The dropsonde gave meteorologists a better look at the true strength of hurricanes, proving they had been underestimating speed of surface winds.

Jeff Masters, chief meteorologist of Weather Underground, said it's not entirely clear why the wind speeds differ from what they expect.

"It's an area of ongoing research," he said. "Hurricanes are complicated."

Forecasters also saw in Andrew that much of the destruction is done on a very localized level.

"A lot of the damage is done by these little tornado-scale vortexes imbedded in the eye wall," Masters said. "There's some very fine scale wind action going on in a hurricane.

Andrew's biggest lesson may be one we're reminded of annually: It only takes one.

Andrew was the first hurricane and the only major hurricane of an otherwise quiet year, an especially pertinent point for a year that's expected to see average or below average hurricane activity.

"You have to assume every year is going to be an Andrew year," Masters said. "You always have to be prepared.

Danny Valentine can be reached at dvalentine@tampabay.com or (727) 893-8804.

Some improvements to hurricane forecasting since 1992

• 2003: Extend track and intensity forecasts from three days to five days.

• 2006: Begin issuing (operational) wind speed probability products.

• 2007: Begin issuing (experimental) storm surge probability products.

• 2008: Begin issuing first series of (operational) storm surge probability products.

• 2009: Begin issuing categorical genesis forecasts for disturbances (low/medium/high chance of formation) in Graphical Tropical Weather Outlook.

• 2010: Watch/warning lead times extended by 12 hours (to 48 and 36 hours, respectively).

• 2010: Genesis forecasts issued to nearest 10 percent.

Source: National Hurricane Center

Science of predicting intensity still uncertain 05/18/12 [Last modified: Friday, May 18, 2012 1:51pm]

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