The Pacific Ocean contains nearly half of the water on Earth, covering a third of its surface. The flights that I took as an crewman across this vast expanse of blue in a U.S. Navy P-3 Orion maritime patrol aircraft seemed to take forever.
This gigantic mass of water, with its strong winds and powerful currents, profoundly influences our weather and climate.
As the temperatures and currents of the Pacific change, so does our Central Coast weather.
As I mentioned in last week’s column, the National Oceanic and Atmospheric Administration’s Climate Prediction Center in Camp Springs, Md., indicated that the current La Niña would peak strongly until next spring.
That will bring cooler surface temperatures to seawater in the central and eastern equatorial Pacific.
Jan Null, a former National Weather Service Lead forecaster and Pacific Gas and Electric Company meteorologist, is recognized as an expert on El Niños and La Niñas and their relationship to California’s weather.
According to Null’s studies (see his web page at http://ggweather.com/enso.htm), weak and moderate El Niños give average rainfall along the Central Coast.
However, strong El Niño events can produce about 140 percent of above-normal rainfall for our area and even greater amounts in other parts of the state.
In 1982-83, El Niño produced huge ocean swells and periods of intense rain and flooding. There were more than 43 inches of rain at Cal Poly.
Just 15 years later, an even greater El Niño event occurred and produced 44 inches of rain at the Diablo Canyon Power Plant Ocean Lab. Most of these rain events were evenly spaced and created few flooding problems.
On the other side of the coin, however, La Niña periods usually produce below-normal rainfall, on average about 87 percent of normal on the Central Coast, and even less in Southern California as the storm track is shifted northward.
This La Niña condition can be amplified or reduced by another large-scale ocean water temperature cycle called the Pacific Decadal Oscillation, or PDO.
The PDO is found primarily in the North Pacific. The phases of the PDO are called warm phases or cool phases.
Unlike El Niño and La Niña, the PDO stays in one phase for a lot longer — between 10 and 40 years. The El Niño and La Niña phases usually last for about a year or so.
It appears that we are still in the cool phase of the PDO, which should increase the La Niña effect and produce a greater chance of below-normal rainfall.
These are long-range forecasts, and only time will tell the story.
This week’s forecast
The marine layer has risen this morning to over 2,000 feet and will spill into areas of the North County through the coastal passes and will exert a greater influence on today’s temperatures.
Temperatures will continue to cool, especially in the North County through Monday.
Marine status will be slow to clear from the coastal valleys and may not clear at all from the beaches this afternoon.
Today’s temperatures will range between the high 50s to the low 60s along the beaches. The coastal valleys (San Luis Obispo) will reach the high 60s while the North County (Paso Robles) will range between the low to mid-70s.
Today’s satellite imagery should depict a wobbly upper level cutoff low pressure center approaching the Central Coast.
This system will be cut off from the jet stream and will spin down the California coast with an almost unpredictable track.
If this system moves over the Central Coast, we’ll receive rain. However, if it tracks farther out to sea, we will probably not receive any measurable precipitation.
Nevertheless, it should create drizzle and a few scattered light rain showers tonight through Monday as this system stalls over Central California.
If we receive measurable rainfall, it should range between 0.05 and 0.25 inches in the coastal valleys and up to 0.40 inches in the mountains.
The moisture and instability associated with this upper-level low will lead to the development of numerous showers and thundershowers along the higher terrain of the coastal mountains and in the foothills of the Sierra Nevada tonight and Monday.
High pressure returns Tuesday through Thursday with fair weather and seasonable temperatures.
The charts and models are indicating a series of vigorous low-pressure systems moving into Washington and Oregon states and further up Northern California late next week with increasing winds and rain.
The trail end of one system may move south enough to produce rain showers along the Central Coast on Friday.
Surf and sea report
Today’s 4- to 5-foot northwesterly (310-degree deep-water) swell (with an 8- to 11- second period) will continue at this height and period through Tuesday.
Combined with this northwesterly swell, this afternoon and tonight will be 1- to 2-foot northwesterly (320-degree shallow-water) seas (with a 4- to 6-second period).
A 3- to 5-foot northwesterly (300-degree deep-water) swell (with an 8- to 14-second period) is forecast along our coastline Wednesday.
A series of storms in the Gulf of Alaska will produce a 4- to 6-foot northwesterly (310-degree deep-water) swell (with an 11- to 15-second period) along our coastline Thursday through next Saturday.
Increasing swell conditions are forecast on Oct. 24, 25 and 26.
Arriving from the Southern Hemisphere:
Today’s 1- to 3-foot Southern Hemisphere (190-degree deep-water) swell (with a 13- to 15-second period) will gradually decrease through Tuesday.
Another low-height Southern Hemisphere (190-degree deep-water) swell is forecast to arrive along our coastline next Saturday.
Seawater temperatures will range between 56 and 58 through this 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. To subscribe to his daily weather forecast or ask him a question, e-mail firstname.lastname@example.org.