A heat wave will hit SLO County this Labor Day. See latest forecast

The Central Coast can expect warm-to-hot weather through the final days of August and into the first few days of September.

A gradual cooling trend is expected to begin on Wednesday and last through next Sunday. High pressure over northern Nevada will generate gentle to moderate (8 to 18 mph) Santa Lucia (northeasterly) winds each morning through the Labor Day weekend.

These offshore winds will promote clear skies and warm to hot conditions across the region.

• Inland Valleys (Paso Robles): Highs will range from the upper 90s to low 100s, with Tuesday likely the hottest day at 104 degrees. For comparison, the daily record for Sept. 2 in Paso Robles is 115 degrees, set in 2017.
• Coastal Valleys (San Luis Obispo): Temperatures will rise into the mid to upper 80s by late morning and early afternoon, before cooling as moderate to fresh northwesterly onshore winds (13 to 24 mph) move in.
• Beaches: Most shoreline areas will peak in the upper 60s to low 70s by late morning. South-facing beaches like Cayucos, Avila and Shell Beach will continue warming into the afternoon, reaching the low 80s.

From Tuesday through Thursday morning, subtropical moisture from the southwest will stream across the Central Coast, bringing periods of mid- to high-level clouds.

While this system is not expected to produce rain or thunderstorms in San Luis Obispo or Santa Barbara Counties, the added instability should help mix out the temperature inversion layer, leaving most beaches free of low marine clouds.

Later Thursday, persistent northwesterly winds combined with weakening high pressure over the Desert Southwest will allow the marine layer to redevelop.

Expect nights and morning fog, mist and drizzle along the coast into the following weekend. Inland valley highs will cool into the upper 80s to low 90s, with coastal valleys in the mid-70s and beaches holding in the 60s.

Looking further ahead, seasonal temperatures are expected to continue into mid-September.

Historically, inland valleys such as Paso Robles are hottest in July and August, coastal valleys like San Luis Obispo peak in September and the beaches warm the most in October.

Surf report

Fresh to strong (19 to 31 mph) northwesterly winds along the coastline will generate a 4- to 6-foot northwesterly (300-degree, deep water) sea and swell (with a 5- to 8-second period) through Tuesday, lowering to 3- to 5-feet (with a 5- to 12-second period) on Wednesday through next Saturday.

A 1- to 2-foot southern hemisphere (215-degree, deep water) swell (with a 15- to 17 -second period) will arrive along our coastline on Sunday and remain at this level through Wednesday, fading away on Thursday through Friday.

A broad area of low pressure located several hundred miles south-southwest of the southern tip of Baja California is forecast to develop into a Tropical Cyclone Kiko later this weekend. If this storm develops as advertised, a 3- to 4-foot southerly (185-degree, deep water) swell (with a 12- to 14-second period) will arrive along our coastline next Saturday and Sunday.

Surface seawater temperatures will range between 56 and 58 degrees through next Sunday.

On this date in weather history (Aug. 31)

1971: The low of 84 degrees and high of 108 degrees at Death Valley were the coolest of the month. The average daily high was 115.7 degrees that August, and the average daily low was 93.4 degrees.

2017: A strong temperature inversion layer developed in the coastal regions of San Luis Obispo County that morning. At 7 a.m., SLOWeather.com in western San Luis Obispo reported 55 degrees with gentle northwesterly (onshore) winds and fog, while just a short distance away, but at 1,200 feet of altitude, Tim’s Place in the Irish Hills reported 84 degrees with gentle Santa Lucia (northeasterly/offshore) winds and clear skies.

2020: The Santa Lucia Escarpment Waverider Buoy about 45 miles southwest of the Diablo Canyon nuclear power plant reported a 3- to 5-foot southeasterly (160 degrees) swell, with a 14- to 16-second period from a series of former tropical storms near Baja California. Point Conception, Point Arguello and Point Sal creates a shadow zone along the Pecho Coast for swell trains coming in from a southeasterly direction.

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 X @PGE_John.