good article on hurricane forcasting

[Windsong]

http://www.floridatoday.com

Scientists hone skills, tools to predict hurricane paths
This photo of Hurricane Isidore was taken from inside the storm by a NOAA Hurricane Hunter aircraft. NOAA photo

Forecasters strive to give best answer to question: Where will it go?

BY CHRIS KRIDLER
FLORIDA TODAY

When it comes to hurricanes, most people care about one thing: Where's it going to go?

Researchers are using smarter technology and analysis to improve track forecasts. They do so partly by focusing on areas around the storm that are key to pushing it one way or another.

If you put a marble on a desk and blow on it, you influence where it will roll, researcher Sim Aberson says. Hurricanes are essentially the same, only the desk is the ocean.

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Storm Season 2004

"Basically, a hurricane is steered by the environmental flow," said Aberson, a meteorologist for the National Oceanic and Atmospheric Administration's Hurricane Research Division in Miami.

Steering a hurricane isn't quite as simple as blowing on a marble. Several factors conspire to nudge a hurricane, including areas of low and high pressure, which influence the winds at different heights in the atmosphere.

To understand those factors, researchers drop instrumented capsules from airplanes flying around the storm. The Global Positioning System-equipped "dropwindsondes" take measurements that are entered into computer models to make these simulations more accurate.

Until the early 1990s, statistical models were the state of the art, Aberson said. They made predictions based on the behavior of similar storms in the past.

Now, the models are dynamic and more sophisticated. They use real-time observations and physics to predict the behavior of the atmosphere and, subsequently, weather around the globe.

"They move the fronts along," Aberson said. "They move the high-pressure areas and low-pressure areas."

As everyone knows, however, computers aren't reality. While the models can be very accurate, they can also differ wildly in their predictions.

"The atmosphere is what we call a chaotic system, meaning that if you change something somewhere a little tiny bit, it can make a big change later on," Aberson said. So different models' forecasts for 24 or 48 hours out can show a hurricane heading in several different directions.

In graphic form, the result is a "spaghetti diagram," said Jack Beven, a hurricane specialist at the National Hurricane Center in Miami. It can show tracks snaking all over the place.

Usually, some of the models are right, and some are wrong.

"Sometimes they are all clueless," Beven said. ". . . The usual result of that is a crash-and-burn forecast."

Forecasts doubted

Other times the models agree, but residents don't always trust them.

Although computer simulations in 1999 suggested Hurricane Floyd, a monster just short of Category 5 status, would curve northward, Brevard beach residents evacuated. The eye squeaked by Cape Canaveral, about 100 miles offshore, and the storm turned north to tear into the Carolinas.

"We know that small differences can create big differences in the forecast," Aberson said. That's why researchers are trying to focus on areas that can influence the forecast significantly.

Here's how they do it:

The dynamic computer models are run four times a day, fed with observations from weather balloons, ships, aircraft and satellites. But the ocean is big, and they don't have data for every point. The models have to do some guessing.

So for each of those four major runs, researchers will do an additional 10 runs of the model, tweaking the numbers each time to see which changes will have the biggest impact on the forecast.

They will focus on a place where they don't have fresh data -- a spot in the ocean with no buoys or ships.

They might change the wind speed by a couple of miles per hour for a spot east of the storm. If they see no change in the track forecast, they know it's not important to get real data there.

But if the model foresees a big shift after a subtle wind change, then forecasters know they might need to send a plane to that area to get real observations, to get the most accurate track forecast.

"Because we have chaos, we will never be able to make perfect forecasts," Aberson said. "There will always be errors."

Specialists forecast

It's up to the specialists at the National Hurricane Center to make the fine judgments that turn computer predictions into forecasts that are issued to the public.

"There is no firm process, and there are six of us hurricane specialists here, and each of us have a little different way to go about it," Beven said. He's been a specialist -- one of the elite forecasters at the hurricane center -- since 1999.

Forecasters do a lot of analysis, he said, using the tools they most prefer. Beven has a strong background in analyzing satellite data, so those images play an important role in his forecasts.

Though track forecasts have improved considerably in the past several years, mostly thanks to the computer models, "it's ultimately forecasters' judgment," he said.

Fortunately, it's easier to track the strongest storms, Aberson said, citing last's year's monster Isabel.

"A strong hurricane, it's very symmetric, it's very well-behaved," he said. "They do what we expect them to do."

[yoda]

That's a good article! Thanks for sharing it!

[The Dark Knight]

Good article..... There are some tough days ahead.... Hurricane Forecasting Season 2004.....

[rbaker]

except for issac in the caribbean that dipped sw into the yucatan in 2002 and that was a cat 3 storm. of course you are always going to have exceptions. Cat 3 and above alot of times create there own environment, and go the path of least resistance.

[Derecho]

except for issac in the caribbean that dipped sw into the yucatan in 2002 and that was a cat 3 storm.

All sorts of models showed the dip.

Cat 3 and above alot of times create there own environment, and go the path of least resistance.

Much more rarely than people think (it's often an excuse to wishcast) and it's really only Strong Cat 4s and above.