Transition month brought motley weather mix

With the first day of November, we turned the clocks back one hour to Pacific Standard Time at 2 a.m. Looking back at this October, we found a mixed bag of weather conditions.

On a chronological basis, an area of high pressure often builds at the surface over the Great Basin, producing northeasterly (offshore) winds.

Winds flow from land to the Pacific Ocean and bring a relatively warm and dry air mass to our shoreline, pushing the marine layer far out to sea.

During October, coastal temperatures can actually exceed inland temperatures; the month is often a transition period between the dry and wet season.

Cal Poly is the official location for historical climate data for San Luis Obispo. On average, the high temperature will reach 75.4 degrees with the average low reaching 49.5 degrees at Cal Poly.

This October, the average high temperature was 73.3 degrees, cooler than average.

The first day of October started out warm, with the weather station at Cal Poly reaching 87 degrees, but readings cooled to the mid 60s to low 70s for most of the first part of the month.

The temperature never surpassed 90 degrees at Cal Poly for the entire month, which is somewhat unusual.

In 1987, a scorching heat wave developed in California, and San Luis Obispo was the warmest location for the nation, with 111 degree temperatures recorded at the airport for two days in a row.

Many Cal Poly students who lived in campus housing slept outside, including me.

On Oct. 13 a storm hit the Central Coast and was unlike any other October storm since records have been kept, with many one-day rainfall records for the month broken, especially in the northern part of San Luis Obispo County.

The Department of Water Resources rain gauge on the top of Rocky Butte near San Simeon recorded 13.7 inches of rain.

The SLOweather.com rain gauge in the hills near Los Osos Valley Road and Foothill Boulevard recorded 7.7 inches.

The average total precipitation for October in San Luis Obispo is little less than an inch.

The remarkable aspect about this weather system was that despite the amazing amounts of rainfall, little flooding occurred. This was probably because the earth was so dry and the rain fell over an extended period at a mostly moderate rate.

This storm also produced gale-force southerly winds in many locations. These winds brought in a subtropical air mass, and temperatures were warm and muggy for a few days after the storm.

The southerly winds also produced a northerly flowing ocean current along the coastline and brought a warmer buoy of seawater from the south.

Seawater temperatures along our coastline reached the low 60s. Seawater temperatures usually average 57.7 degrees during October at the Diablo Canyon Power Plant Ocean Lab.

By the later half of the month, a more familiar October weather pattern developed with night and morning northeasterly (offshore) winds followed by afternoon northwesterly (onshore) winds.

These offshore winds produced warm temperatures in San Luis Obispo with late morning and early afternoon highs reaching into the low to mid-80s.

At the end of the month, a steep pressure gradient developed along our coastline and produced gale-force northwesterly winds and much cooler temperatures.

Wind gusts at Diablo Canyon reached 52 mph on Tuesday. These winds also produced a greater amount of upwelling and much cooler seawater temperatures along the immediate coastline, dropping to the mid-50s.

Normally, the average wave height at the Diablo Canyon waverider buoy during the month of October is 4.6 feet, but this October the average height was one of the highest at 5.6 feet.

This was good news for the surfers but bad news for the fisherman.

This week’s forecast

An area of high pressure over the Great Basin will produce gusty northeasterly (offshore) winds, especially in the eastern part of San Luis Obispo and our coastal canyons this morning.

Temperatures should warm rapidly through the morning hours, with today’s highs ranging between the low to mid 80s throughout our area by early this afternoon.

The winds will shift out of the northwest (onshore) to moderate to fresh (13-to 24-mph) levels, producing cooling along the coastline and the coastal valleys.

These onshore winds will also allow a few areas of low clouds to develop along our northwesterly facing beaches during the late afternoon and evening hours.

Otherwise, clear weather with another night of cool temperatures is expected.

This pattern of cool nights and warm days will continue through most of this upcoming week as a 1,028 millibar Eastern Pacific high parks itself off the California coastline, keeping the storm track far to the north for an extended period.

Surf and sea report

This morning’s 3- to 5-foot northwesterly (310-degree deep-water) swell (with a 7- to 22-second period) will increase to 5 to 7 feet (with an 11- to 20-second period) later this morning and will continue at this height but with a gradually shorter period through Tuesday.

This northwesterly swell will decrease to 3 to 5 feet (with an 8- to 13-second period) on Wednesday and will continue at this height and period through Thursday.

A 4- to 6-foot northwesterly (310-degree deep-water) swell (with an 8- to 18-second period) will arrive along our coastline on Friday, increasing to 6 to 8 feet (with a 15- to 17-second period on Saturday.

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To the amazingly bright students at Grover Heights Elementary School in Grover Beach: remember, northeasterly (offshore) winds often produce clear and warm weather.

John Lindsey is a media relations and nuclear communications representative for Pacific Gas and Electric Co. He is also a meteorologist who specializes in forecasting for San Luis Obispo County. Send him questions to pgeweather@pge.com.