Better tools on the way for hurricane forecasters

The government forecasters will be the first to admit they have room for improvement.

The National Hurricane Center did a good job of telling where Irene was headed but overestimated its fury. That's partly because traditional forecast models use low-resolution data, said James Franklin, chief of the hurricane-specialist unit.

Translation: Information on temperature, pressure, and wind speed is gathered by sensing equipment that is dropped by parachute every 150 miles over the ocean - an imprecise picture at best.

Better forecasting tools are in development, however, including one at Pennsylvania State University that relies on higher-resolution data captured by airborne Doppler radar.

The Doppler radar planes are aloft for at most 12 hours a day. But the result is far more precise, with data collected every few hundred yards - sort of like having many more megapixels in a camera. This information is in turn fed into a sophisticated model that requires massive amounts of computing power.

Penn State meteorology professor Fuqing Zhang cautioned that no model can be evaluated on the basis of one storm.

But for what it's worth, Penn State's Doppler-aided model had Irene pegged pretty closely, correctly predicting that the storm would weaken by the time it reached New Jersey on Sunday morning.

At 8 p.m. Aug. 23 - the Tuesday before the storm - the Penn State model predicted that Irene would slow to about 80 miles per hour by 8 a.m. Sunday - soon after it was expected to hit New Jersey. The actual speed at that point was 75 miles per hour, Zhang said. The official government forecast had the wind speed above 100.

Franklin, the government forecaster, said Zhang's results from dozens of previous storms were "very promising."

"It may be one of our best hopes for trying to find models that can depict these kinds of changing conditions," he said.

Still unclear is just what happened to sap Irene's energy, but there are theories, Franklin said.

The strongest winds in a hurricane are found in a ring around the eye, called the eyewall. Often a second ring will develop outside the eyewall and start to contract, stealing energy from the original eyewall until it dissipates and disappears. The process then repeats.

But in Irene, it seems that multiple outer eyewalls developed, diffusing the available energy, Franklin said.

"Instead of having a single, well-defined outer eyewall that could take over, we seemed to have a whole series of outer rain bands," Franklin said. "Irene remained this very large, broad, diffuse system with no well-defined focus for intensification."

This apparently caused the storm to weaken between the Bahamas and North Carolina, despite the warmer-than-normal ocean temperatures that would ordinarily have fed its strength.

"A hurricane is like a heat engine," Zhang said. "It takes the energy from the ocean and converts it to motion."

"That's why [the weakening] was so peculiar," Franklin added.

By the time Irene hit New Jersey soon after 5:30 a.m. Sunday, its sustained winds barely registered the minimum hurricane speed of 74 miles per hour - and that speed was seen only over water east of the Garden State, Franklin said.

What about the rest of the year? More big storms are expected, though it's tough to say whether they will make landfall, much less hit the Mid-Atlantic, according to researchers who focus on long-term forecasts.

The Atlantic is in the midst of a 25-to-35-year cycle of greater-than-average hurricane activity, and this year is predicted to fit that trend, said Colorado State University research scientist Phil Klotzbach.

Activity is measured, among other ways, by "accumulated cyclone energy" - a figure calculated from the square of wind speeds of the various storms. (Some scientists think the storms are on the rise because of human-induced climate change; Klotzbach is not among them.)

Normally by the end of August, the accumulated cyclone energy is 32. So far this year, with the help of Irene, we've hit 38.

Earlier this year, Colorado State's Tropical Meteorology Project predicted the total for the season would hit 165, based on statistical analysis of ocean-water temperatures and wind patterns. The long-term average is just 106.

Keep rain gear handy.