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Environment

Dance of death: a Pacific Ocean typhoon does the do-si-do with a tropical storm — and then mostly cannibalizes it

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As Japan's Himawari satellite watched, Typhoon Noru and Tropical Storm Kulap did a do-si-do in the northwest Pacific — and then Noru pretty much slurped up Kulap. (Infrared imagery: Cooperative Institute for Meteorological Satellite Studies. Animated gif: Tom Yulsman) It has been expected for awhile, and now it has finally happened: Two tropical systems in the Northeast Pacific spun around each other in a kind of cyclonic do-si-do — and then the bigger one ate most of the smaller one. As of Tuesday evening (in the U.S.), the cannibal cyclone, Typhoon Noru, has continued on with Category-1-strength winds of about 70 knots, according to the Joint Typhoon Warning Center. Meanwhile, a remnant of the victim, Tropical Storm Kulap, has spun off as a puny little tropical depression. To be completely accurate, the move wasn't a classic do-si-do. That's because in square dancing, each partner spins around the other but keeps facing in the same direction. Meanwhile, cyclones pinwheeling around each other are also spinning themselves. This is a phenomenon known as the Fujiwhara effect. It happens when two cyclones come within about 900 miles of each other, You can see it all happening in the animation of satellite images above. The infrared imagery was acquired by the Himawari satellite over the course of two days, starting on July 23th, 2017. Meanwhile, far to the east, two other cyclonic partners are preparing for their own square dance: https://twitter.com/NOAASatellitePA/status/889899016682713092 In the animation above, two hurricanes swirl to the west of Mexico on Tuesday, July 25, 2017. Hurricane Irwin is to the left, and Hillary to the right. Here's a static view, acquired by NASA's Terra satellite:

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Hurricanes Irwin (to the left) and Hillary (to the right), as seen by NASA's Terra satellite on Tuesday, July 25, 2017. (Source: NASA Worldview) Right now, they're happily dancing on their own. But weather models predict that they are likely to draw close enough to do a Fujiwhara do-si-do on Thursday. Since Hillary is bigger and stronger, it should be the dominant partner, capturing Irwin and eventually gulping it down after four or five days. Here's what that process should look like: https://twitter.com/pppapin/status/889949617315557377 That's a bloody fabulous animation, don't you think? We'll soon see whether things develop in just this way.

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