Dancing Storms: The Case of Hilary and Irwin (Image credit: NOAA NHC)

Discussion: As Tropical Depression Hilary continues to degenerate this evening, Tropical Storm Irwin remains. However, a few days before dissipating, Hilary and Irwin were interacting in a rare phenomenon called the Fujiwhara effect. The Fujiwhara effect, named after Japanese meteorologist Sasuke Fujiwhara is a meteorological phenomenon where two cyclones within a distance of 600 to 900 miles from each other begin to orbit each other around a center point between them, like two pinwheels. The two cyclones, now attracted to each other will begin to move closer until they merge into one system. However, this is not always the case, as sometimes they will move away from each other, though typically one storm, typically the larger one will absorb part of the other (smaller) storm, causing one to intensify, and the other to weaken.
. Ironically, it was predicted that Hilary would absorb Irwin, as it was stronger at the time, yet as I noted above, Hilary has degenerated, and Irwin is still active. Although, their trajectory was changed due to the orbiting effect of the Fujiwhara effect, the two storms don’t look like they will be merging completely as expected either, at least not yet.  Even more unusual, these two storms were experiencing the Fujiwhara effect on the same day a pair of Western Pacific tropical cyclones, Typhoon Noru and Tropical Storm Kulap were experiencing the Fujiwhara effect as well. Hilary and Irwin experienced the latter, with them orbiting each other, but not merging. While these two storms may not have followed the prediction exactly, it is interesting to see this rare phenomenon happening in two places on the same day.
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