Thirty-Five Million Under Alert as California Bakes

There is a particular unease that comes with heat in October—a month that should carry the first hints of autumn, the softening of summer's grip, the promise of cooler days ahead. In California this weekend, that promise has been broken. A multi-day heat wave of unusual intensity for the season has settled over nearly the entire state, placing more than 35 million people under heat alerts and pushing temperatures 20 degrees above normal from the San Francisco Bay Area to the Mexican border .

The numbers tell a story of dangerous extremes. On Saturday, at least eight Southern California cities broke daily high-temperature records. Anaheim and San Diego both reached 105 degrees. Santa Ana hit 107. In Vista, north of San Diego, the mercury climbed to 108—breaking a daily record and tying an all-time high set in 1985 . An excessive heat warning remains in effect across Southern California, including Los Angeles, Riverside, and Temecula, where highs are expected to reach triple digits. San Diego, also under an excessive heat warning, is forecast to see temperatures in the upper 90s. The warnings will remain in place until Thursday evening .

What makes this heat wave particularly concerning is its duration and its behavior at night. In urban areas especially, warm overnight conditions will provide little to no relief, compounding the cumulative stress on the human body. Prolonged exposure to high temperatures without nighttime recovery increases the risk of heat illness, particularly for the elderly, the very young, those without air conditioning, and people who work outdoors .

The heat is expected to expand east over the coming days across the Great Basin, with highs in the 80s and near 90s. Meanwhile, flood watches are in effect along the Gulf Coast and in Florida, a reminder that the same atmospheric patterns driving the Western heat are producing contrasting extremes elsewhere .

For Californians, the advice is familiar but urgent: drink plenty of fluids, remain in air-conditioned spaces when possible, check on neighbors and relatives, and limit outdoor activities to the early morning or evening hours. The heat wave is a reminder that climate patterns are shifting in ways that extend the reach of summer well into the months that once belonged to autumn. The records broken this weekend are not anomalies. They are part of a pattern that scientists have long warned would intensify as the planet warms .

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Sources: ABC News, National Weather Service, Good Morning America