The tracks of Hilary and Irwin are shown overlaid on this analysis of accumulated rainfall.

Dancing cyclones: The 'Fujiwhara effect'

The Fujiwhara effect is a rare phenomenon that sees nearby cyclones ‘dancing’ round each other. In July it was seen not once, but twice*: Hurricanes Hilary and Irwin rotated round each other in the Eastern Pacific Ocean off the coast of Mexico generating high surf for Southern California; whilst thousands of miles away in the western Pacific east of Japan just days earlier, Typhoon Noru and Tropical Storm Kulap spun round each other*.

If the Tropical Cyclones are similar in size, they can move around one another for a few days, before taking their own paths. However, if the Tropical Cyclones are of different sizes, then the larger of the two will tend to dominate, with the smaller one orbiting around it. Sometimes, the smaller Tropical Cyclone will be consumed by the larger one and the two systems essentially merge, with the smaller storm dissipating and the larger storm remaining and moving away on its own.

This is what happened in these situations: Hurricane Irwin was consumed by the stronger and larger Hurricane Hilary which then moved northwest before dissipating; whilst Kulap was consumed by Noru, which strengthened but remained over open water.

*Although this was not a full Fujiwhara interaction, since Typhoon Noru’s path was not affected by the other storm.

Credit: Around Us

Categories: Weather
Tags: Extreme Weather Storms Tropical Cyclones WorldWeather

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