Weather Watch

Obsolete lighthouses are comforting

Many times while sailing the Pacific Gas and Electric Co. oceanographic vessels at the Diablo Canyon nuclear power plant southward down the Pecho Coast, I was reassured to hear the foghorn and see the light of the Point San Luis Lighthouse while heading to Port San Luis.

Even with today’s modern satellite electronic navigational tools, I always felt more comfortable seeing that friendly light.

I can only imagine what it must have of been like navigating the coastal waters of California before modern navigation equipment and weather forecasts were available. These lighthouses were and are still vital in keeping your boat off the rocks. They also act as navigational aids.

The Point San Luis Lighthouse was first lit on June 30, 1890, with a fourth order Fresnel lens that was manufactured in Paris. The original lens served the Central Coast until 1969, when it was replaced by an automated electric light. In 1974 the U.S. Coast Guard moved the modern beacon from the lighthouse to the top of the nearby Coal House.

In 1995, the nonprofit group Point San Luis Lighthouse Keepers was formed to take on the responsibility of restoring the lighthouse. After many visits, I can tell you that they have done a tremendous job of restoring this jewel of the Central Coast.

Depending on the height of your vessel, weather and oceanographic conditions, the light from the Point San Luis Lighthouse can be seen 16 miles out to sea.

Generally speaking, lighthouses come in many shapes and sizes. There is no average height. The height of the light is often determined by local conditions.

In 1881, the Point Conception light was moved from the top of a bluff halfway down to a point 133 feet above the Pacific because the marine layer would often obscure the light.

The current Point San Luis light is about 116 feet above sea level. This height was chosen by its designers to keep it below the marine layer, but high enough for ships far out at sea to be able to navigate safely through coastal rocks and reefs.

If the light was too low in height, captains couldn’t see it. For example, if you are surfing at sea level, you can see about 1.2 miles before the curve of the Earth hides an object from sight. If you are 100 feet above the ocean, you can see about 12.3 miles out to sea.

Refraction of light caused by atmospheric conditions, such as a temperature inversion layer over the water, can cause you to see something that’s actually over the physical horizon. That’s why we don’t have exactly 12 hours of light and darkness during the first day of spring or fall.

The lighthouses along the Central Coast have their own light characteristics, providing a secure navigational tool.

If you were to travel southward from Big Sur to Point Conception, you would probably first notice the Piedras Blancas Light, which flashes white every 15 seconds. As you continue southward, you would see the Point San Luis Light, which flashes every 20 seconds. Heading further southward on your journey, you would observe the Point Conception light, which flashes every 30 seconds.

If you’re interested in hiking along the Pecho Coast Trail and visiting this beautiful lighthouse, visit www.pge.com/recreation for more information.

This week’s forecast

This morning’s calm and clear conditions will allow temperatures to reach near the freezing level in the interior valleys of San Luis Obispo County. Morning lows will be warmer in the coastal valleys and along the beaches.

Today’s high temperatures should only reach the high 50s to the low 60s as an unseasonably cold weather system moves toward San Luis Obispo.

A vigorous cold front associated with a 987-millibar low-pressure system off the Northern California coast will approach our area this Easter morning and spread fresh to strong (from 19 to 31 mph) southeasterly winds and moderate rain southward into the Central Coast by this evening through tonight.

Rain will turn to showers Monday as an upper-level trough passes over San Luis Obispo County. Total rainfall amounts should range from a half an inch to an inch.

Heavy snow is expected across the Sierra tonight and Monday.

Snow levels will be initially at 3,000 and 4,500 feet north to south, dropping to 2,000 to 3,000 feet north to south by Monday morning. This storm has the potential to produce snowfall accumulations of 6 to 10 inches in the 2,500 to 3,500 foot elevation range by early Monday morning.

Gusty northeasterly (offshore) winds during the morning hours Tuesday and Wednesday will produce fair, dry and warmer weather.

Wednesday will be the warmest day of the forecast period with temperatures in the mid-70s.

Increasing northwesterly (onshore) winds Thursday and Friday will produce cooler temperatures and night and morning low clouds and fog along the coast.

Surf and sea report

This morning’s 9- to 11-foot northwesterly (300-degree deep-water) swell (with an 8- to 15-second period) will remain at this height and period all the way through Tuesday, decreasing to 8 to 10 feet Wednesday.

Combined with this northwesterly sea/swell will be 3- to 5-foot southerly (190-degree shallow-water) seas this evening through tonight.

Strong to gale force (25-38 mph) northwesterly winds will produce a 7- to 9-foot northwesterly (310-degree deep-water) sea/swell (with a 5- to 12-second period) on Thursday; seas will remain at this height and period through Saturday.

Seawater temperatures will range from 52 and 54 degrees through Wednesday, decreasing Thursday and Friday.

Arriving from the southern hemisphere: Today’s 2- to 3-foot southern hemisphere (200-degree deep-water) swell (with an 18- to 20-second period) will arrive Friday, increasing to 2 to 4 feet on Saturday.

John Lindsey is a media relations representative for Pacific Gas and Electric Co. He is also a local weather expert and has lived along the Central Coast for more than 23 years.

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