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ARI SHAPIRO, host:

This is MORNING EDITION from NPR News. I'm Ari Shapiro.

STEVE INSKEEP, host:

And I'm Steve Inskeep. Good morning.

Forecasters are watching a system of thunderstorms in the Caribbean today. They're trying to figure out whether the system will organize into a tropical storm or even a hurricane. In fact, they're always asking how powerful a storm will become. That question certainly baffled forecasters earlier this month when a similar group of thunderstorms quickly became Hurricane Karl and slammed into Mexico.

As Karl developed from minor weather disturbances to major trouble, researchers had it under a microscope. And as NPR's Jon Hamilton reports, they're hoping that what they saw in Karl will help them predict the power of future storms and save lives.

Unidentified Man #1: Attention in the cabin, seatbelt sign is on. Make sure your lap belts...

JON HAMILTON: With Hurricane Karl just hours from the Mexican coast, a plane full of researchers sets out from Fort Lauderdale to overtake the storm.

Mr. MICHAEL BLACK (National Oceanic and Atmospheric Administration): It's a mad race to try and get there before the center's totally onshore.

HAMILTON: Michael Black works for the National Oceanic and Atmospheric Administration. He says the researchers want to get as much data as possible on Karl, because it has strengthened dramatically and unexpectedly.

Mr. BLACK: You've got a storm that a day ago was barely a hurricane and turned into a Category 3 in a matter of about 18 hours. That's a huge difference in preparation and plans when you've got a hurricane bearing down on you.

HAMILTON: Forecasters simply didn't think Karl would become a major hurricane. So as the scientists fly west, Mexican officials and the media are scrambling to warn people about the approaching storm.

(Soundbite of waves crashing)

Unidentified Woman #1: (Foreign language spoken)

HAMILTON: An emergency has been declared for the coast of Mexico and people are evacuating. Black and the other scientists are flying today as part of a massive effort to prevent surprises like this. Ed Zipser of the University of Utah says forecasters have become very good at saying where a hurricane will go. But he says they're not so good at predicting how strong a hurricane will be when it arrives.

Professor ED ZIPSER (University of Utah): We are behind in that. And we don't do as good a job because we don't completely understand the process.

HAMILTON: They know that water temperature and prevailing winds can limit a storm's strength. But these don't explain why storms like Karl can intensify so rapidly. So for more than a month, NASA has been sending out up to a half dozen planes to search for clues in every storm that passes within reach.

The plane we're on today is a modified DC-8, packed with instruments that measure everything from particles in the atmosphere to the height of cloud tops.

Unidentified Man #1: OK. He's going to make it at 1747, so we've got two and a half minutes to go.

HAMILTON: By the time the plane reaches Karl, the storm's eye wall is already touching land. And on the ground in Veracruz, residents are feeling the storm.

(Soundbite of rain)

HAMILTON: One family that rode out the storm at home captured the experience with a video camera.

Unidentified Man #2: (Foreign language spoken)

Unidentified Woman #2: (Foreign language spoken)

HAMILTON: Miles above the chaos, the scientists work quickly to take measurements before the storm is completely onshore.

Unidentified Man #3: Five, four, three, two, one. Bombs away.

HAMILTON: They launch canisters that parachute toward the ocean, sending back information about winds, pressure, temperature and humidity. They begin pulling data from onboard radars. Black says that will reveal things you can't see from a satellite.

Mr. BLACK: You can view those as sort of a CAT-scan of the storm. We'll be able to peer in and look at the structures of rainfall and winds within the storm, all in a three-dimensional volume.

HAMILTON: And this NASA mission includes data from a new source - an unmanned aircraft that can fly at extremely high altitudes for 25 hours at a stretch.

Unidentified Man #1: We just passed (unintelligible) point 14 on the flight plan.

HAMILTON: As the DC-8 follows Karl inland, the scientists try to figure out how bad things are on the ground. Ed Zipser is looking at data from an area where the storm is colliding with a 10,000 foot mountain.

Prof. ZIPSER: As the winds blow this moist air up the mountain, we don't have any idea if it's going to be a beneficial rain or a disastrous rain.

HAMILTON: The plane's radar expert is Simone Tanelli from the Jet Propulsion Laboratory at Caltech. He's worried about a spot in the foothills with very intense rain.

Mr. SIMONE TANELLI (Jet Propulsion Laboratory, Caltech): It was coming down more rain than what you can imagine. And the nasty thing, the thing that scares me a little bit in regards to the people that live in that spot, if for one hour it kept raining like that, those people must be under a meter of water. I don't know what...

HAMILTON: The DC-8 has followed the storm as far as it could and has to turn back to base. News reports are already beginning to describe widespread damage.

(Soundbite of broadcast)

Unidentified Woman #3: Mexico's Veracruz and Puebla states have taken a pounding from Hurricane Karl. When the deadly storm roared through Mexico's south central region, it downed trees, billboards and power lines. Thousands were forced to evacuate and local forecasters say the storm dumped eight inches in some areas in only 90 minutes. Saturday...

HAMILTON: Before it was done, Hurricane Karl would kill at least 16 people and cause billions of dollars of damage.

But scientists on the DC-8 may have found some clues to explain why Karl grew so fast. One tantalizing possibility is that when clouds known as hot towers form, a storm may be about to intensify. These towers carry hot moist air through the high layer of cirrus clouds that form above a hurricane. They go so high that scientists have had trouble studying them until now. Black says he thinks he'll get good data from the unmanned aircraft known as Global Hawk.

Mr. BLACK: That aircraft is flying about 60,000 feet. They get a very clear view, plus very detailed measurements, with their radars onboard, of these hot towers that will pop up though this thick cirrus shield of clouds.

HAMILTON: And perhaps, tracking those hot towers will finally lead to earlier warnings of deadly storms.

Jon Hamilton, NPR News.

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