Condition creates eye-catching sight

As in most years, those of us who live along the beaches of San Luis Obispo County have awakened to marine overcast, fog and drizzle for most of the summer.

At times, the drizzle has been heavy enough to produce measurable precipitation. The weather reporting station in Baywood Park has recorded more than a tenth of an inch of drizzle since July 1. Despite the warmer temperatures and clear skies last Wednesday, the Baywood Park weather station still hasn’t recorded temperatures above 70 degrees since May 5.

The eclectic coastal community of Los Osos hasn’t experienced many clear sunsets this past summer. However, as we approach fall, increasing high pressure over the Great Basin — the area between the Sierra Nevada range to the west and the Rocky Mountains to the east — often produces night and morning offshore winds, pushing the marine layer far out to sea. This treasured condition allows the coastal communities to watch the often eye-catching Pacific sunsets.

For most of the day, the star in the middle of our solar system produces white light so intense that it causes pain from just looking at it with your naked eye. When directly overhead, the sun’s light travels through the thinnest part of the atmosphere.

This mighty light fades as the sun moves closer to the horizon. It changes its color and that of the sky around it with ever-increasing hues of oranges and reds. As the light from the sun moves into the thickest part of the atmosphere, the sun looks larger and its intensity decreases to the point that you can now look directly at its trailing edge as it disappears below the horizon. (But please remember, it is never safe to look directly into the sun without proper equipment.)

Dr. Jim Bevan of Cambria, who worked many years with the U.S. Navy in atmospheric physics, told me, “As the sun sets, it passes through ever-longer stretches of the atmosphere. The upper atmosphere quickly scatters out virtually all shorter wavelengths of the light spectrum such as blue light.” He went on to say, “Soon the less-efficiently scattered green, yellow and orange light are also removed from the incident solar spectrum. The last remaining light eventually becomes predominantly red since red light is the color that has the weakest molecular scattering.”

Smoke from fires can produce even more profound effects on the sun’s light.

The smoke particles scatter out most of the remaining red light.

9/11 remembrance

On this date 10 years ago, a steady light rain fell upon San Luis Obispo, like so many tears from angels. May we always keep the victims and their families of the Sept. 11 attacks in our thoughts and prayers.

Weather report

An upper-level low-pressure system, centered near Santa Cruz Island, will drift northward toward San Luis Obispo over the next 48 hours. This system will continue to tap into monsoon moisture, resulting in bands of thunderstorms moving counterclockwise toward the Central Coast through Monday.

Thunderstorms may be accompanied by lightning, gusty winds, heavy rain and hail; unfortunately, they can also be accompanied by dry lightning, which can produce a fire hazard.

Because there is no well-defined front associated with this type of system, exact timing of thunderstorms and rain amounts are difficult to predict. In other words, periods of sunshine or mostly cloudy skies may last for extended periods before bands of thunderstorms or rain showers roll through your area.

The periods of sunshine will lead to a more unstable atmosphere, producing greater chances of towering puffy cumulus clouds.

A few areas in San Luis Obispo County may not receive measurable precipitation while other areas could see up to half an inch.

The lightning tracker at www.SLOweather.com is a proficient tool to look out for thunderstorms.

This subtropical moisture has scoured out the marine layer along the Central Coast and is not expected to redevelop until Tuesday morning. Only subtle changes in high temperatures are expected over the next seven days.

September averages about 0.33 inches of precipitation in San Luis Obispo. On Sept. 10, 1976, the remnants of Hurricane Kathleen reached the county. Kathleen was a hurricane for only six hours, but it took an unusual path northward through Baja California. It crossed the U.S.-Mexico border near El Centro east of San Diego, as a tropical depression. Kathleen produced gale-force winds and widespread flooding in many parts of the West, especially in California’s Imperial Valley.

Subtropical moisture from this storm produced 1.72 inches of rain in San Luis Obispo on Sept. 10 and 11 alone.

Surf report Arriving from the northwest:

Today’s 3- to 5-foot northwesterly (295-degree deep-water) swell (with an 8- to 11-second period) will decrease to 2 to 4 feet with the same period Monday.

Fresh to strong (19- to 31-mph) northwesterly winds along the Pecho Coast will generate a 3- to 5-foot northwesterly (310-degree deep-water) sea and swell (with a 4- to 11-second period) along our coastline Tuesday and Wednesday.

Today’s charts are indicating a 990-millibar storm developing in the Gulf of Alaska today with 45-knot northwesterly winds.

This storm should produce a 4- to 6-foot northwesterly (290-degree deep-water) swell (with an 8- to 11-second period) Thursday through Friday, decreasing to 3 to 5 feet Saturday.

Arriving from the Southern Hemisphere:

Southern Hemisphere swell reached the NOAA SE Hawaii marine buoy stationed about 185 nautical miles southeast of Hilo Saturday morning at 4 feet with a 16-second period. That was higher than predicted.

A 2- to 3-foot Southern Hemisphere (210-degree deep-water) swell (with a 16- to 18-second period) is forecast along our coastline Tuesday and Wednesday.

Seawater temperatures

Seawater temperatures will range between 56 and 59 degrees through today, increasing to 57 to 60 degrees Monday.

Seawater temperatures will decrease to 55 to 58 degrees Tuesday through Friday.

Emergency preparedness kit

Prepare and maintain an emergency kit with enough supplies to be self-sufficient for at least three days and preferably up to one week. To learn more, please log onto http://www.pge.com/myhome/edusafety/ naturaldisaster/emergencyprepare/

John Lindsey, media relations representative for PG&E and local weather expert, has lived along the Central Coast for more than 25 years. To subscribe to his daily weather forecast or ask him a question, email him at pgeweather@pge.com.