What was actually seen in the images was a compact manifestation of the Catalina eddy.

It’s also known as a coastal eddy and is a common occurrence in a body of water from Santa Barbara to San Diego known as the Bight of California.

The bight is formed by a mostly convex part of the Southern California coast.

Mountainous terrain just inland from San Diego to metropolitan Los Angeles blocks the prevailing northwesterly wind flow, sending it back out to sea to a focal point near Santa Catalina Island.

If coastal low cloudiness blankets the bight as the eddy forms, it becomes visible in the deck of low overcast.

The image to the right was captured by NASA’s Aqua satellite just before 3 p.m. Pacific Standard Time on February 17. At that time, the eddy had become wrapped tight like the eye of a hurricane about 25 miles to the west of San Diego. As it spun out around sunset, the eddy drifted back northward, never approaching the coast.

Catalina eddies can develop at any time of the year. But they are most common between April and September when they bring welcome cool breezes to the densely populated coastal strip of Southern California during summertime. The center of the eddy is most often located near or directly over the island of Santa Catalina.

While the vortex is relatively small, rarely more than 100 miles in diameter, it can extend into inland valleys and even into southwestern parts of the Mojave Desert. A very strong Catalina eddy can extend upward to about 6,000 feet above sea level.

Full story and image: NASA