As most beach goers will tell you, this summer has seen numerous days of overcast and drizzly weather. Not only has the atmosphere been chilly, but the waters along the immediate coastline have remained downright cold, and the harbor seals and sea lions seem to want to spend more time on the rocks and beaches.
Stronger than normal northwesterly winds have produced a greater amount of upwelling along the coastline. Combined with a strengthening La Niña (colder than normal ocean water in the equatorial and eastern Pacific), that has produced below-normal sea water temperatures throughout this summer.
In fact, up to this August, the sea water temperature has averaged a record-breaking 53 degrees at the Diablo Canyon Nuclear Power Plant, the lowest since seawater temperature records started being kept in 1976. Normally, it averages about 57 degrees during August.
The name La Niña, meaning “the girl,” originates from Spanish; it’s analogous to El Niño, meaning “the boy” or “the Christ child,” which produces above-normal sea water temperatures.
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For reasons we really don’t understand, pressure areas change places at irregular intervals over the equatorial Pacific. This is part of the broader El Niño-Southern Oscillation climate pattern.
During the La Niña phase, high pressure builds in the eastern equatorial Pacific while low pressure develops to the west, producing a stronger equatorial pressure gradient. Almost like a car rolling downhill, the easterly trade winds strengthen, causing upwelling off Peru’s and Ecuador’s coastlines to intensify and lowering sea surface temperatures throughout the Eastern Pacific Ocean, including along the Central Coast.
Most of the models indicate that La Niña will continue to strengthen through the early part of winter.
The good news is that upwelling brings nutrients to the surface waters off the coast, allowing the fish populations living in these waters to thrive. Unfortunately, this condition often shifts the storm track further northward into the Pacific Northwest and Northern California, leaving the Central Coast high and dry with below-average rainfall.
I reviewed my weather forecasts from past La Niña events during the winter and found that nighttime temperatures are often colder and daytime temperatures warmer than normal. In other words, a greater temperature spread develops between the day and night.
This is primarily due to lack of insulating cloud cover during the night and mostly sunny conditions during the afternoon, but the lack of prefrontal southerly winds also plays a part in increasing the temperature spread.
These are long-range forecasts and should be taken with a grain of salt.
A cold front, like the March 1995 storm, could easily stall over the Central Coast and produce copious amounts of rain and prove this long-range forecast wrong. Only time will tell the story.
Today’s weather forecast
A dying cold front will pass the Central Coast this late August morning with coastal low clouds and drizzle. A steep pressure gradient behind this cold front will produce strong to gale force (25 to 31 mph) northwesterly (onshore) winds along the coastline this afternoon and well below-normal temperatures throughout San Luis Obispo County.
The northwesterly winds will mix out the temperature inversion layer, producing mostly clear and sunny conditions along all of our beaches late this morning through this evening.
Today’s temperatures will range from the low to mid-60s along the northwesterly-facing beaches (Los Osos, Morro Bay and Cambria), while the southwesterly-facing beaches (Avila Beach and Cayucos) will warm to the low 70s. The coastal valleys (San Luis Obispo) should range between the high 60s and the low 70s. The North County will cool to the mid- to high 70s.
Except for a few areas of morning coastal low clouds, widespread clear skies and continued warming will occur Monday. The warming trend will continue Tuesday as high pressure builds across the state in combination with moderate to fresh (13 to 24 mph) northerly winds.
Further warming is expected Wednesday and Thursday, with temperatures near to slightly above normal Thursday.
At this time, it looks as though still another cooling trend will begin Friday and last into the Labor Day weekend as another low-pressure system from the Gulf of Alaska dives southward toward the Central Coast.
Surf and sea report
This morning’s 3- to 5-foot northwesterly (320-degree deep-water) sea and swell (with a 5- to 8-second period) will increase to 4 to 6 feet this afternoon and tonight, further building to 5 to 7 feet (with a 6- to 8-second period) on Monday.
This northwesterly (310-degree deep-water) sea and swell will decrease to 4 to 5 feet Tuesday.
Increasing northwesterly winds along the Northern California coastline will produce a 5- to 7-foot (320-degree deep-water) sea and swell (with a 7- to 9-second period) along the Central Coast on Wednesday through Thursday.
A 3- to 5-foot northwesterly (295-degree deep-water) swell (with an 8- to 10-second period) is forecast Friday and Saturday.
Arriving from the Southern Hemisphere: Today’s 1- to 3-foot Southern Hemisphere (180-degree deep-water) swell (with a 14- to 16-second period) will gradually decrease through Monday.
Tropical storm Frank off the southern Baja Peninsula is too far east to produce any swell along our coastline. A series of swell trains from the Southern Hemisphere will approach our coastline from a very southerly (175-degree deep-water) direction next week and will have little effect.
Seawater temperatures will range between 51 and 54 degrees through most of next week.
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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 23 years. If you would like to subscribe to his daily weather forecast orask him a question, send him an e-mail at firstname.lastname@example.org.