SLO County weather forecast: Changing to spring-like weather pattern, windy

This week we’ll see considerable changes in the weather from subtropical rain, high relative humidity levels (muggy) along with a chance of thunderstorms this weekend, transitioning to a spring-type of weather pattern with strong to gale-force (25 to 38 mph) afternoon northwesterly winds, fog and mist during the night and morning and much cooler temperatures on Tuesday through next Sunday.

The remnants from Tropical Storm Kay will produce primarily cloudy skies and rain showers (heavy if a convective cell moves over your area) throughout San Luis Obispo County with a chance of thunderstorms.

The European Centre for Medium-Range Weather Forecasts and NOAA’s global forecast systems models indicate between 0.10 and 0.60 of an inch of rain this weekend. High dew-point temperatures and extensive cloud cover will produce warm overnight lows.

Sunday’s high temperatures will range between the low-70s along the beaches. The coastal valleys (San Luis Obispo) will reach the low-80s, while the high-80s are expected in the inland valleys (Paso Robles).

Monday will be a transitional day with decreasing clouds and increasing northwesterly winds as the ridge of high pressure responsible for the hot temperatures will move toward the east. Consequently, strong to gale-force (25 to 38 mph) afternoon northwesterly (onshore) winds and a cooling trend we’ll start Tuesday and continue through next Sunday.

This onshore flow will also allow the marine layer with night and morning fog and mist to develop and deepen in the coastal regions.

Surf Report

Thunderstorms may develop over the ocean on Sunday. They can produce heavy rainfall, lightning, gale-force downbursts winds, and in turn, rough seas and even waterspouts.

Sunday’s 3- to 5-foot northwesterly (290-degree, deep-water) swell (with an 8- to 11-second period) will remain at this level into Monday.

Strong to gale-force (25 to 38 mph) northwesterly winds will generate a 5- to 7-foot (310-degree, deep-water) sea and swell (with a 5- to 8-second period) on Tuesday and remain at this level through Friday, increasing to 6- to 8-feet with the same period next Saturday and Sunday.

Tropical cyclones are expected to develop west of the International Dateline and become extratropical as they move into the North Pacific. If these storms become extratropical, the fall’s first long-period west-northwesterly swell could arrive along our coastline by the end of September.

A 1- to 2-foot Southern Hemisphere (200-degree, deep-water) swell (with a 13- to 15-second period) is expected along our coastline on Sunday, decreasing Monday.

Seawater temperatures will range between 58 and 61 degrees through Monday, decreasing on Tuesday through Friday to 54 to 57 degrees.

This date in weather history

1976 - Up to five inches of rain brought walls of water and millions of tons of debris into Bullhead City, AZ via washes from elevations above 3000 feet. Chasms up to forty feet deep were cut across some roads.

2001 - A low pressure center off our coastline pulled subtropical moisture over our area this morning, producing extensive cloudiness and sprinkles, conditions that fitted this tragic day.

2017 - This morning’s convective cells (thunderstorms) produce rain showers and interesting wind patterns. The Diablo Canyon Meteorological Tower recorded a brief downburst with sustained Northerly winds of 33 mph with gusts to 51 mph at 2 a.m. while other San Luis Obispo County locations remained relatively calm. WWW.SFGate.com reported 54 mph winds at Pebble Beach at 2:30 a.m., while only 10 minutes away in Monterey conditions remained still. This pattern of spotty-brief downbursts were reported throughout the Bay Area early this morning.

This week’s temperatures

LOWS AND HIGHS, PASO ROBLES

LOWS AND HIGHS, SAN LUIS OBISPO AND COASTAL VALLEYS

John Lindsey is a retired PG&E marine meteorologist. Email him at JohnLindseyLosOsos@gmail.com or follow him on Twitter @PGE_John.Surf report

This story was originally published September 11, 2022 at 5:00 AM.