Heat wave headed to SLO County, with temperatures above 100 degrees

A classic Central Coast early summer weather pattern will continue through the beginning of this week with night and morning low marine clouds and mild to warm temperatures, but a big change is on the horizon.

The first extended heat wave of the year is expected to arrive later this week and continue through the following week as an area of high pressure moves westward over Arizona.

Temperatures in Paso Robles could reach as high as 110 degrees, while San Luis Obispo is expected to hit the 90s. Along the immediate coastline, the low-marine (stratus) clouds will keep the coastal communities mainly in the 60s and 70s.

A few of the long-range models indicate that this area of high pressure will migrate northeastward toward the Four Corners area by late July.

Historically, when this condition occurs in July or August, it can push subtropical moisture into the Central Coast, producing increasing relative humidity levels with a chance of thunderstorms. In other words, it can transform our weather pattern to resemble Florida.

In the meantime, persistent northwesterly (onshore) winds will continue to produce night and morning low-marine clouds with pockets of fog and mist in the coastal regions. Fresh to strong (19 to 31 mph) northwesterly winds will develop during the afternoon, producing clearing.

Sunday’s high temperatures will reach the high 80s in the inland valleys (Paso Robles) and the mid-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 mid-70s. This pattern will continue through Friday.

The National Weather Service predicts triple-digit temperatures could reach Paso Robles by Wednesday and rise from there.

Surf report

Fresh to strong (19 to 31 mph) northwesterly winds along the coastline will generate 5- to 7-foot northwesterly (300-degree, deep-water) sea and swell (with a 5- to 9-second period) during the afternoon and night through Friday.

A 3- to 5-foot northwesterly (290-degree, deep-water) swell (with an 8- to 11-second period) is forecast along our coastline on Saturday into Sunday, decreasing to 2 to 4 feet throughout next week. Combined with this northwesterly swell will be 1- to 2-foot southern hemisphere (225-degree, deep-water) swell (with a 15- to 17-second period) next weekend.

Seawater temperatures will range between 53 and 55 degrees through Friday, increasing to 56 to 58 degrees next weekend.

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.

This story was originally published July 9, 2023 at 5:00 AM.