The pattern is known to meteorologists as a Catalina eddy, or coastal eddy, and it forms as upper-level flows interact with the rugged coastline and islands off of Southern California. The interaction of low- and high-pressure systems—with offshore winds blowing out of the north and coastal winds blowing out of the south—give the marine stratus clouds a cyclonic, counter-clockwise spin. The eddy is named for Santa Catalina Island, one of the Channel Islands offshore between Los Angeles and San Diego.
Catalina eddies can bring cooler weather, fog, and better air quality into Southern California as they push the marine boundary layer further inland. These mesoscale eddy patterns can stretch across 100 to 200 kilometers (60 to 120 miles) and can last from a few hours to a few days. They most often form between April and October, peaking in June.
A downloadable time-lapse video from the GOES-West weather satellite is linked below the image and shows the evolution of the eddy over roughly eight to ten hours. Images of the pattern in other wavelengths are available on the CIMSS Satellite Blog.
- Mass, C. F. and Albright, M.D. (1989) Origin of the Catalina Eddy. Cite>Monthly Weather Review, 117, 2406–2436.
- NOAA National Weather Service Glossary. Accessed March 8, 2013.
- University of Wisconsin-Madison (2013, February 17) Eddy off the coast of southern California. CIMSS Satellite Blog. Accessed March 8, 2013.
- Aqua - MODIS - NASA