Summer’s here, but the cool weather is continuing. When will SLO County heat up?

Summer has arrived, but you wouldn’t know it from the weather.

A series of weak upper-level low-pressure systems will travel southward along the Central California coastline in the coming days. These systems will continue to produce below-normal temperatures, night and morning marine low clouds, and increasing northwesterly winds during the afternoon through Tuesday.

Low-marine clouds with pockets of fog and mist will greet Sunday morning. Fresh to strong (19 to 31 mph) northwesterly winds will develop during the afternoon, producing clearing.

Sunday’s high temperatures will reach the low-80s in the inland valleys (Paso Robles) and the low-70s in the coastal valleys (San Luis Obispo). The beaches will warm up to the mid-60s, except the southerly-facing beaches of Cayucos, Avila Beach and Shell Beach, which will warm to the low-70s. This pattern will continue through Tuesday.

A robust early summer upper-level low-pressure system will develop off the California coastline on Wednesday and remain nearly stationary through Friday. This system will produce a deep marine layer with areas of drizzle during the night and morning, gentle to moderate northwesterly to southwesterly (onshore) winds, and below-normal temperatures.

The long-range models indicate increasing northwesterly winds, clearing skies, and warmer temperatures starting next Sunday and continuing through July 4.

An area of high pressure is expected to develop and strengthen over the Four Corners area by mid- to late July, producing the first triple-digit temperatures of the year in the inland regions, just in time for the Mid-State Fair.

Surf report

Fresh to strong (19 to 31 mph) northwesterly winds along the coastline will generate 4- to 6-foot northwesterly (300-degree, deep-water) sea and swell (with a 5- to 11-second period) during the afternoon and night, decreasing to 3- to 5-feet during the morning. This pattern will start Sunday and will continue through Tuesday.

A 3- to 5-foot northwesterly swell (with an 8-to 12-second period) is forecast along our coastline on Wednesday through Friday. Combined with this northwesterly swell will be 1- to 2-foot southern hemisphere (200-degree, deep-water) swell (with a 14- to 16-second period) on Wednesday through Friday.

Last week’s gale-force northwesterly winds produced large amounts of upwelling. Consequently, seawater temperatures lowered to 51 degrees at the PG&E Diablo Canyon Waverider Buoy. Seawater temperatures will range between 51 and 54 degrees through Tuesday, increasing to 55 to 57 degrees on Wednesday into Friday.

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.