News - Local

Saturday, Jul. 04, 2009

John Lindsey: Wind-driven waves offer potential energy source

Comments (0) |

I am always amazed when I stand on the shore and watch the waves breaking along our beaches.

Some of the waves may be visiting us from afar — possibly traveling up to 7,000 miles before crashing along the Central Coast.

In the summer when we see southerly swells, it’s likely the surf came from a storm off the coast of New Zealand more than 10 days before.

That’s a long way for mechanical energy to travel, but a ticket to ride or watch one of these waves is free of charge.

The long-period, higher-energy waves usually come from extratropical cyclones.

These are known as mid-latitude storms. These storms usually cover a much greater area than a hurricane and can produce winds just as strong as a Category 1 hurricane (74 to 95 mph).

These winds transfer tremendous amounts of energy to the ocean in the form of waves.

I have seen “significant swell heights” (defined as the average height of the waves in the top third of the wave record) from these midlatitude storms reach over 55 feet at the SE PAPA marine buoy.

That buoy is moored about 600 miles west of Eureka, in the mid-eastern Pacific.

The offshore buoys are referred to as the weather sentinels of the sea, and they always indicate at least one wave train or another arriving from some part of the Pacific on a continuous basis.

Significant wave height turns out to be very close to what an experienced mariner — “old salt” — would perceive the wave heights to be.

Maximum wave height may be up to twice as high for a particular event.

Over the many years that I’ve forecasted waves along the Central Coast, I’ve never seen it go completely flat — or less than one foot in height.

Ocean waves move along routes that mark out great circle tracks.

A great circle track is the shortest distance between two points on a sphere like the Earth. That’s why airliners fly over Alaska to reach Japan; it’s a much shorter distance versus a route marked by a straight line across a map of the Pacific.

The longer the wavelength or period of the wave, the faster it will travel across the ocean.

As a general rule, the average speed of wave trains traveling across the deep waters of the Pacific is about 25 mph per hour or about 600 miles per day.

The longer the wavelength of a wave, the greater amount of energy it holds.

Initial studies suggest that the energy harnessed from these waves could make a significant contribution to California’s renewable energy goals.

Pacific Gas & Electric Co. is proposing a wave energy pilot study to be conducted off the coast of Humboldt County in Northern California.

If approved, it would be less than 200 acres in size and would give wave energy conversion device manufacturers the opportunity to test their devices on a common site and facilitate the development of wave energy technology.

For more information, please visit www.pge.com. Information about the WaveConnect project can be found in the Environment section under “What We’re Doing/Clean Energy Solutions.”

Next week we will talk about the differences between drizzle, rain showers and gentle to heavy rain.

This week’s forecast

Today’s charts are indicating a change in the weather pattern as an upper-level low moves across the state.

This condition will cause the pressure gradients to tighten up along the Central Coast and produce a slight increase in northwesterly winds this afternoon and significant increase on Monday through Friday.

Temperatures will range between the low to mid 90s in our inland areas, the mid to high 70s in the coastal valleys and the mid 60s to the low 70s at the beaches.

Absolutely gorgeous Central Coast weather is on tap today.

This upcoming week’s fresh to strong (19- to 31-mph) northwesterly (onshore) winds will produce a deeper marine layer and cooler coastal temperatures on Monday.

The increasing northwesterly (onshore) winds should be strong enough to mix out the coastal low clouds and fog during the late morning and afternoon hours Tuesday through Friday.

A strong high-pressure ridge will begin to build across California from the southwest, bringing warmer temperatures next weekend and potentially very hot temperatures the following week.

Surf forecast

A 1- to 2-foot northwesterly (315-degree deep-water) swell (with a 7- to 11-second period) will continue at this height through this morning.

Today’s charts are indicating increasing northwesterly winds as the pressure gradients tighten up along the Central Coast this afternoon through next week.

These winds will generate 1- to 3-foot (325-degree shallow-water) seas (with a 3- to 5-second period) this afternoon through tonight, increasing to 3 to 5 feet on Monday through Tuesday morning.

These northwesterly (325-degree shallow-water) seas will further increase to 5 to 7 feet (with a 4- to 7-second period) on Tuesday afternoon and will continue at this height and period through Saturday.

Arriving from the southern hemisphere:

This morning’s 2- to 3-foot southern hemisphere (200-degree deep-water) swell (with a 15- to 17-second period) will continue at this height and period through Saturday.

John Lindsey is a communications representative and meteorologist for Pacific Gas and Electric Company in San Luis Obispo. If you have a question, e-mail him at pgeweather@pge.com.