An area of deep low pressure off the California coastline butted against a strong Eastern Pacific high and produced near-hurricane-force winds over the ocean about 700 miles to west-northwest of San Luis Obispo on March 31. These winds generated huge seas, reaching nearly 40 feet in height. As the sea moved under these fierce winds, it created long-period swells traveling eastward toward the Central Coast.
These swells arrived along the San Luis Obispo County coastline April 1. They peaked at 16 feet with an 18-second period at the Diablo Canyon Waverider buoy.
That was the biggest swell event since Jan. 19, 2010, when the Waverider buoy reached 19 feet with an 18-second period. The Cape San Martin NOAA marine buoy, stationed 55 nautical miles northwest of Morro Bay, reached even higher, at 23 feet.
These breakers lashed the shore and whipped up copious amounts of sea foam. Since April 1, I have received numerous emails asking about sea foam. Sea foam is common along the Central Coast, especially during higher wave events and periods of plankton blooms.
Irving Berlin wrote the lyric, “To the oceans white with foam,” in the patriotic song “God Bless America” made famous by Kate Smith.
Sea foam is formed by the agitation of the seawater caused by crashing waves, especially when it contains large amounts of dissolved organic matter. Along the Central Coast, plankton blooms combined with decaying bits and pieces of red, green and brown algae can put a lot of dissolved organic material in the water column in the form of proteins and fats.
Like fluffy whipped egg whites, the proteins in the seawater become denatured — changed from their natural state — as they are churned by breaking waves in the surf zone.
As the large denatured protein molecules unfold in the churning seawater like origami flowers, the air-loving part of the proteins stick to the air bubbles. The air bubbles in the foam become more persistent through surface tension. This is pretty much how sea foam develops.
Because of the light weight and persistence of sea foam, it can be easily blown onshore by winds onto beachfront sidewalks and streets.
Overall, the majority of sea foam is not harmful to humans. In fact, it is often an indication of a healthy and productive ocean ecosystem.
However, when sea foam is made from a harmful algal bloom such as dinoflagellates (red tide), the aerosols from its popping sea foam bubbles can pose a health risk for those with asthma or other respiratory conditions. It can also irritate the eyes of beach-goers.
If sewage, detergents or oils from polluted storm water are present, the resulting sea foam can be more persistent. Sometimes when the conditions are just right, large amounts of sea foam can accumulate along the coast and conceal large rocks and voids, making hiking along the beaches hazardous.
Today’s weather report
A ridge of high pressure over California combined with this morning’s gentle to moderate (8- to 18-mph) northeasterly (offshore) winds have produced clear and sunny weather this Easter Sunday. This morning’s minimum temperatures in the North County will drop to the freezing level. This should be the last morning of freezing temperatures for the season. Temperatures this afternoon will rise to the mid-70s in North County and the high 60s in the coastal valleys (San Luis Obispo) and along the beaches. Mostly clear skies, gentle winds and mild temperatures will continue through Monday afternoon.
A 996-millibar low-pressure system will move toward California later Monday. This system will produce coastal low clouds with areas of fog and gentle to moderate (8- to 18-mph) southerly winds Monday night into Tuesday morning.
The associated cold front will approach the Central Coast on Tuesday with increasing mid- to high-level clouds and moderate to fresh (13- to 24-mph) southeasterly winds. A few rain showers should begin to fall Tuesday afternoon, turning to a steady rain Tuesday night into Wednesday morning with the frontal passage. Rain showers will taper off by Wednesday afternoon. This is a warmer system, and snow levels should remain above 5,000 feet. Rainfall amounts should range between 0.25 and 0.75 of an inch in the coastal valleys, with greater amounts in the coastal mountains.
Another low-pressure system will approach the Central Coast on Thursday, with moderate rain spreading across San Luis Obispo County later Thursday into Friday morning. Rain will turn to a few showers by Friday afternoon. Because of the longer days and greater amount of instability, thunderstorms could develop with this system. Strong to gale-force (25- to 38-mph) northwesterly winds will develop Friday afternoon to Friday night. Snow will continue in the Sierra on Friday night, then decrease Saturday morning. Total rainfall amounts from this system should range between 0.5 and 1 inch.
Dry, clear and warmer weather will develop this Saturday through next Sunday. Dry weather will continue through the following week.
Today’s surf report
This morning’s 3- to 4-foot northwesterly (300-degree deep-water) swell (with an 8- to 14-second period) will remain at this height and period through this afternoon.
A 4- to 6-foot west-northwesterly (285-degree deep-water) swell (with an 11- to 15-second period) will arrive along the Pecho Coast tonight, increasing to 6 to 8 feet (with an 11- to 13-second period) Monday. This swell will decrease to 4 to 6 feet (with an 11- to 13-second period Tuesday, further lowering to 3 to 5 feet (with a 9- to 15-second period) Wednesday.
Combined with this northwesterly swell Tuesday and Wednesday will be 2- to 4-foot southerly (190-degree shallow-water) seas.
A 4- to 6-foot westerly (275-degree deep-water) swell (with an 11- to 15-second period) will arrive along the Central Coast on Thursday, shifting out the west-northwest and building to 8 to 10 feet (with an 8- to 17-second period) Friday.
Seawater temperatures will gradually increase to 50 to 52 degrees Monday, further rising to 51 and 53 degrees Tuesday through Thursday.
Earth Day event
Join PG&E employees Saturday to celebrate Earth Day at Montaña de Oro State Park.
The event is one of a number of service projects sponsored by PG&E and the California State Parks Foundation. Please register at the California State Parks Foundation website, www.calparks.org/programs/earth-day.
Be sure to dress for outdoor work with long pants, long-sleeved shirt, sturdy shoes, hat, gloves and sunscreen. Snacks and lunch will be provided. Bring your own refillable water bottle. Rangers will provide tools and supervision.
John Lindsey is a media relations representative for PG&E. He is also a local weather expert and has lived along the Central Coast for more than 25 years. If you would like to subscribe to his daily weather forecast or ask him a question, send him an email at email@example.com.