SLO County weather forecast for the week of Oct. 3: Cooling trend and a chance of rain

Overall, July and August are the warmest months in the inland valleys, September in the coastal valleys, and October along the coastline.

Typically, by October, the coastal marine clouds along the beaches give way to mostly blue skies until the first storms of the year arrive. Usually, in fall, the coastal regions become warmer than the inland areas as the Santa Lucia (offshore) winds develop during the night and morning.

You see, all it takes is a slight change in the direction or speed of the winds to make the difference between a clear and or a foggy day.

However, this first week of October will see gentle to moderate (8- to 18-mph) southerly to northwesterly (onshore) winds, a deepening marine layer with pockets of night and morning fog and mist along the beaches on Sunday through Wednesday. The inland regions will remain clear; however, the coastal valleys will see night and morning low clouds.

Combined with low marine clouds in the coastal areas, will be variable amounts of smoke and haze, mostly above 6,000 feet of altitude, that will continue to stream over the Central Coast from the wildfires burning in the central and southern Sierra Nevada.

Sunday’s high temperatures along the shoreline will range from the low to mid-60s, while the coastal valleys (San Luis Obispo) will vary between the low to mid-80s. The inland valleys will warm to the mid-90s, with Paso Robles reaching 97 degrees on Sunday.

A cooling tread will develop on Monday and will continue through the week. In fact, the inland valleys will only reach the 70s and the coastal valleys the 60s by Thursday.

An approaching low-pressure system will bring increasing clouds and areas of fog and drizzle throughout the Central Coast on Thursday. As this low-pressure system develops west of the Central Coast on Friday into Saturday, rain showers could advance across San Luis Obispo County.

However, current forecast models are in inferior agreement regarding precipitation amounts, and details are quite unclear.

The ECMWF (European Centre for Medium-Range Weather Forecasts) indicates between 0.25 and 0.50 of an inch of rain, while NOAA’s GFS (Global Forecast System) is dryer at less than 0.10 of an inch on Friday into Saturday.

In any event, it looks like widespread below-average temperatures with a chance for wet and unsettled weather across Central California later in the week and continuing into next weekend.

The following week is expected to see gale-force northwesterly winds, high sea and swell, and below-average seasonal temperatures.

Surf report

Sunday’s 4- to 6-foot northwesterly (295-degree, deep-water) swell (with an 8- to 14-second period) is forecast to continue along our coastline through Monday.

A 3- to 5-foot northwesterly (300-degree, deep-water) swell (with an 8- to 12-second period) is expected along our coastline on Tuesday through Wednesday.

Another 3-to-5-foot northwesterly (295-degree, deep-water) swell, but (with an 11- to 18-second period) is forecast along our coastline on Thursday into next Sunday.

A 9- to 11-foot northwesterly (310-degree, deep-water) sea and swell (with a 7- to 14-second period) will develop along our coastline next Monday, Tuesday and Wednesday, October 11, 12 and 13.

Seawater temperatures will range between 57 and 60 degrees on Sunday through this week.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

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John Lindsey’s is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.