Can Hurricanes Collide?

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I know, hurricane season is almost over (Nov. 30), and I meant to post about this earlier this season. It's a frequently asked question of blog readers and AccuWeather.com Facebook Fans. Until last month's WeatherWise Magazine came out, I didn't have a good answer for it.

Q: Can hurricanes cross paths or collide? If so, do they make a superstorm?

A: Short answer: Yes, very rarely they can collide but weakening is more likely because the outside winds are going in different directions. If they just get close to each other, their rotation can cause them to spin around each other (this answer is more well-known: It's called the Fujiwhara Effect. This happens at least once a year in the West Pacific, but only once ever few years in the Atlantic. Long answer: Check out Tom Schlatter's article at WeatherWise, which mathematically explains the figure above, supplied by The COMET Program.

Storms colliding are extremely rare, especially if you don't count non-tropical low pressure systems such as the 1991 Halloween Storm. The only example that the article gave was 1995's Hurricane Iris which merged with and absorbed Tropical storm Karen, after spinning Fujiwhara-style. Technically, it was a threesome, with Humberto also involved).

Their tracks are shown below and I have labeled the approximate location of "M" in the diagram above -- although that diagram assumed storms were coming from opposite direction. In this case, Karen pinwheeled northwestward around got sucked into Iris. Is the Iris/Karen interaction technically a collision? I don't know but the satellite loop shown above (obtained from my alma mater) is actually really cool to see!

The National Hurricane Center says"Iris began a Fujiwhara interaction on the 30th, with Tropical Storm Karen to its southeast. The interaction swept the weaker Karen on a spiral path around, and then into, Iris where it was absorbed on September 3rd. The interaction could have contributed to Iris' erratic motion during this period."

For more discussion of the Fujiwhara Effect, see the video below.

Although WikiPedia describes the interaction between 1997 Joan and Ivan as "the most noteable example," the tracks showed that they didn't rotate around each other, but followed similar paths as a results of Fujiwhara (meh). The other example Kate shows above was Ione and Kirsten 1974, which still wasn't impressive as 1995 but caused very erratic tracks.

Interestingly, half of the Fujiwhara storms WikiPedia listed for the Pacific and Atlantic were named between I and L, which is either a coincidence or they are even more rare early or late in the season.