THE WEATHER BEAT · EXPLAINER · SEP 30

What a heat watch is telling you: Southern California gets two days' notice of a long, hot week

The Oxnard and San Diego offices issued an Extreme Heat Watch on Wednesday for heat that starts Friday. Here is what the two days of notice are for, and.

By the Weather Rock September 30, 2026, 1:37 p.m. · 6 min read

The Ventura Pier in Ventura, California, photographed on 13 March 2026. Photo: Busition, Wikimedia Commons, CC BY 4.0.

Key points

On Wednesday, 30 September, the National Weather Service offices in Oxnard and San Diego put the coast and valleys of Southern California under an Extreme Heat Watch, from Friday morning into the middle of next week.
The watch forecasts highs up to 90 at the coast and up to 105 to 108 in the valleys. In the San Diego office's area, lows near the coast are expected to stay in the lower to mid 70s from the weekend on.
A watch is the early notice. It tells you the heat is possible and gives you two days to prepare before the watch window opens.

Explainer: what a heat watch is telling you, two days early

On Wednesday morning, two Weather Service offices in Southern California issued an Extreme Heat Watch for a stretch of coast running from the Santa Barbara Channel to the Mexican border. San Diego issued it at 3:05 a.m. PDT and Los Angeles/Oxnard at 9:46 a.m. PDT. Neither one starts until Friday morning. That gap is the point of a watch, and this week's heat is a good way to see how the product works.

A watch comes before a warning. The Weather School's lesson on the three headlines puts it this way: a watch means early and wide, and a warning means here and now. When a watch goes up on Wednesday for heat that starts Friday, the office is saying the conditions are lined up and the hot days are likely enough that you should plan around them. It is not saying the heat has arrived. Both products say the same thing in their additional details. Oxnard expects very hot temperatures to continue into the second week of October and says the watch may need to be extended. San Diego calls it a long-duration heat wave that develops late this week and runs through much of next week into the following weekend.

What makes this one worth reading slowly is how long it lasts and how warm the nights stay. The Los Angeles and Ventura watch runs from Friday morning to 8 p.m. PDT Thursday, 8 October. The San Diego watch runs to 9 p.m. PDT Wednesday, 7 October. Along with the afternoon highs, the San Diego product gives the overnight low: the lower to mid 70s from the coast into the western valleys during the weekend, "with those warm overnight temperatures continuing for next week." A heat product that names the low is telling you to plan for the nights as well as the afternoons.

The products also say what to do, and the list is short. Drink plenty of fluids. Stay in an air-conditioned room. Stay out of the sun. Check on relatives and neighbors. Never leave children or pets in a parked car. In both offices' words, "car interiors will reach lethal temperatures in a matter of minutes."

If the heat arrives as forecast, a watch like this one usually gives way to a warning as the days get closer. If it doesn't, the office cancels it. Either way, the Weather Service is using the two days a watch gives you.

Watch area	Office	Forecast highs, per the product	Window
Los Angeles and Ventura County coast and valleys, including Downtown Los Angeles, the San Fernando and San Gabriel valleys, Santa Clarita, Ojai, Malibu, Catalina	NWS Los Angeles/Oxnard	up to 90 at the coast, 105 in the valleys	Fri 2 Oct morning to 8 p.m. PDT Thu 8 Oct
Santa Barbara County coasts, Santa Ynez Mountains, interior mountains, Cuyama Valley, Santa Cruz and Anacapa Islands	NWS Los Angeles/Oxnard	up to 85 at the coast, 100 in the mountains and Cuyama Valley	Fri 2 Oct morning to 8 p.m. PDT Thu 8 Oct
Orange County, San Diego County coast and valleys, the Inland Empire, Santa Ana Mountains and foothills	NWS San Diego	around 90 near the coast, upper 90s to 108 in the valleys; lows lower to mid 70s coast to western valleys from the weekend	Fri 2 Oct morning to 9 p.m. PDT Wed 7 Oct
HeatRisk, San Diego area	NWS San Diego	Moderate or greater for coast and valleys; Major to Extreme for inland coastal areas into the western valleys	through next week

*Source: NWS Los Angeles/Oxnard CA Extreme Heat Watch, sent 9:46 a.m. PDT 30 September 2026 (16:46Z), and NWS San Diego CA Extreme Heat Watch, sent 3:05 a.m. PDT 30 September 2026 (10:05Z), read from api.weather.gov at 17:35Z. Times are Pacific Daylight Time.*

This is a summary, not emergency information. For live warnings see weather.gov and your local officials. The Los Angeles/Oxnard office posts its products at https://www.weather.gov/lox/ and the San Diego office at https://www.weather.gov/sgx/.

The rock's live forecast for the places in this story