Fujiwhara Effect: Here's why the wind was so intense in San Francisco

Drew Tuma Image
Wednesday, March 22, 2023
Fujiwhara Effect: Why the wind was so intense in the Bay Area
It is fair to say that Tuesday's storm was unprecedented. ABC7 News meteorologist Drew Tuma explains the Fujiwhara Effect here.

SAN FRANCISCO (KGO) -- An unprecedented storm swirled over the West Coast on Tuesday, with winds so strong in San Francisco that it had residents wondering what was going on.

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A satellite view of the storm showed what appeared to be almost the classic look of a hurricane, with an eye-like formation directly over San Francisco -- although the mechanics of how hurricanes form are quite different.

The reason this happened is a rare meteorological effect that's a dance between two areas of low pressure. It's coined the Fujiwhara Effect.

What ABC7 News meteorologist Drew Tuma says essentially happened is there were two areas of low pressure basically competing. Initially, one area of low pressure slammed into Santa Cruz, creating issues. It was eventually absorbed by an area of low pressure just off of our coastline.

As those two formed together in the afternoon Tuesday, it rapidly strengthened into one storm. That's part of the reason why we saw such an intense system.

Initial guidance thought it was going to be a single area of low pressure moving in, but it turned out to be two areas of low pressure that were duking it out, seeing who would win.

Eventually one absorbed the other, which is actually very rare.

When that happens, it strengthens into the one storm that just happened to occur right over San Francisco, which is why we had such intense winds on Tuesday.

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