Hurricane Hilary and Tropical Storm Irwin, both churning in the Eastern Pacific off Mexico, are about to start a rare, circular dance – what’s known as the Fujiwhara Effect.
The Fujiwhara Effect -- named after a Japanese researcher who discovered this in the 1920s – is defined by the National Weather Service as “a binary interaction where tropical cyclones within a certain distance of each other begin to rotate about a common midpoint.”
A similar phenomenon just occurred in the West Pacific, where two storms, Noru and Kulap, underwent a dance of their own.
Irwin is a tropical storm about 1,080 miles off the southern tip of Baja California, Mexico, while Hilary – a Category 1 storm churning west-northwest -- is about 540 miles off Baja California.
By the time Hilary speeds up to it, Irwin will be a weaker storm — far too weak to take on its younger sister.
"Since it has the smaller circulation of the two," forecasters said, "it is likely to suffer and be the one that loses intensity."
Neither Hilary or Irwin are expected to become a threat to the islands, though they're still too far away to know for sure.
And forecasters also don't know what to expect when the two storms meet since computer models differ. But they believe the storm will weaken, especially as it hits colder waters.