Mesoscale Eddies

I got to play Ask Doctor Science today at work. A caller reported that the water at Kailua Beach was up to the vegetation line, and that the beach had pretty much disappeared. He wanted to know what was going on.

The quick answer: beaches are dynamic, there is seasonal erosion and that the beach should be naturally replenished over the winter, and that Kailua Beach is accreting over the long term.

I dug around a bit more [i.e. asked Dolan and Chris, our coastal guys], and learned that we are witnessing an anti-cyclonic mesoscale eddy. In layman's terms, eddies are slow-moving 100-200 kilometer wide storms in the ocean. From the surface the one passing over O`ahu appears to be a 60-cm high hill of warmer water.

The Naval Research Laboratory has some great animations on the eddies.