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ARI SHAPIRO, host:

And now for something that is made offshore: hurricanes. Of course, this is hurricane season, so we watch them, track them, worry about them - but here's something that we haven't done just yet: weigh them. Here with his scale is NPR science correspondent Robert Krulwich.

ROBERT KRULWICH: I know this is an odd question, so I wanted to ask the right guy.

Mr. ANDY HEYMSFIELD (National Center for Atmospheric Research): I'm a senior scientist at National Center for Atmospheric Research. I've been here almost 35 years and my field has to do with clouds.

KRULWICH: So as a distinguished cloud scientist, I wondered if Andy Heymsfield could tell me how much does a hurricane weigh? Meaning, if you could freeze a hurricane just for an instant, how many pounds of water does a classic hurricane carry in the air?

Mr. HEYMSFIELD: It's very, very big.

KRULWICH: Well, I figured. But Andy said youre going to be so surprised how much water is up there, maybe we should do this in smaller steps. Let's start, he said, with...

Mr. HEYMSFIELD: A little cloud.

KRULWICH: Okay. How much water is in a little white, you know, puffy cloud? And he said...

Mr. HEYMSFIELD: To put those numbers into perspective, what I did was I went through modeling calculations.

KRULWICH: And rather than use pounds, Andy says he prefers to measure clouds using units of water that are elephant sized. I said why elephants?

Mr. HEYMSFIELD: Because it's something that one can immediately imagine. And you know also, elephants suck up a lot of water.

(Soundbite of laughter)

Mr. HEYMSFIELD: And store that. And so just think of them as a big water balloon.

KRULWICH: Okay.

Mr. HEYMSFIELD: And now I'm going to put everything in elephant units.

KRULWICH: Okay. So you tell me, please, if an elephant weighs roughly four tons, how many elephant weights of water are there in a little cloud?

Mr. HEYMSFIELD: A hundred elephants.

KRULWICH: A hundred elephants. In a baby cloud? You sure?

Mr. HEYMSFIELD: A very small little puffy cloud.

KRULWICH: Because a little cloud doesnt look big enough to carry that kind of weight.

Mr. HEYMSFIELD: Well, I think the dimensions are somewhat deceiving.

KRULWICH: Clouds, he says, look small when youre down on the ground, but very often they are much bigger than you think.

Mr. HEYMSFIELD: Yeah. The dimensions are very large. And this is just a small little puffy cumulus cloud.

KRULWICH: Well, let's do it bigger. Let's step it up. Let's make it a storm cloud.

Mr. HEYMSFIELD: Well, how about a cumula-nimbus?

(Soundbite of hurricane)

KRULWICH: A cumula-nimbus cloud is so heavy with water that just the uptake of vapor...

Mr. HEYMSFIELD: The updrafts entering into that cloud would be equivalent to 500 elephants a second.

(Soundbite of laughter)

KRULWICH: So the cloud is absorbing 500...

Mr. HEYMSFIELD: Yeah.

KRULWICH: ...elephants a seconds of water as it...

Mr. HEYMSFIELD: That's right. And thats...

KRULWICH: And you have to think of clouds as dynamic. They pull things in and they shed things out all the time.

Mr. HEYMSFIELD: That's right.

KRULWICH: So then how many elephant units of water are there in a storm - a regular storm cloud?

Mr. HEYMSFIELD: We are talking a huge number.

KRULWICH: What is it?

Mr. HEYMSFIELD: Something like 15 million elephants in the air in condensed form.

KRULWICH: Gee.

Mr. HEYMSFIELD: It's very, very big.

KRULWICH: Okay. So now we're ready for hurricanes. I guess they're completely off the charts?

Mr. HEYMSFIELD: The scale is just unimaginable, how big these storms are.

KRULWICH: Okay. So did you choose a particular hurricane?

Mr. HEYMSFIELD: I took a large hurricane - Hurricane Rita - that was 2005.

KRULWICH: In Houston. And the number you got?

Mr. HEYMSFIELD: Okay. About 100 million.

(Soundbite of thunder)

KRULWICH: So Hurricane Rita carried 100 million elephants worth of water, that's the weight, just floating in the sky...

Mr. HEYMSFIELD: In the air. Yeah. Yeah...

KRULWICH: ...worth of water.

Mr. HEYMSFIELD: ...at a given time. Yeah. That's right.

KRULWICH: So the lesson here is what a hurricane really does is it lifts enormous amounts of water from one part of the Earth to another.

Mr. HEYMSFIELD: It is doing very heavy lifting.

KRULWICH: And if anything, we have understated the grandeur of all this, because had we used the usual animal metaphor for rain, you know the one?

Mr. HEYMSFIELD: Yes, raining cats and dogs.

KRULWICH: In cat and dog units, the hurricane would carry - go ahead.

Mr. HEYMSFIELD: Let's see, 10 - 20 billion cats and 20 billion dogs. That's a lot of them.

KRULWICH: That's a lot of hurricane.

Mr. HEYMSFIELD: More cats and more dogs than there are in the planet.

KRULWICH: Robert Krulwich, NPR News.

SHAPIRO: Okay. So you may be wondering if a little cloud weighs tens of thousands of pounds, how does it manage to stay afloat? Well, Robert Krulwich has that answer for you in a cartoon, at npr.org/science.

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