Why is San Diego so hot right now?

San Diego's mild weather depends on one thing: a steady breeze off a cool ocean. Most days, air flows from the Pacific onto land, often under a lid of marine-layer cloud, and keeps the coast in the 60s and 70s. When San Diego suddenly bakes, especially in fall, that breeze has usually reversed.

The Santa Ana flip

Santa Ana winds form when high pressure builds over the Great Basin, the cold high desert of Nevada and Utah. Air flows out of it toward the low pressure off the coast, which means it pours west, over the mountains and down into the coastal valleys. As that air sinks it is squeezed by rising pressure, and compression heats it. It arrives warm and very dry, and it pushes the marine layer and sea breeze offshore.

2026 has been a hot one

• —March 8: San Diego hit 89°F, a record for the date, during a Santa Ana event.
• —Labor Day (Sept. 7): the city reached 95°F, another record, with the coast and valleys in the 90s and 100s.
• —Early October: an extreme heat warning had highs 15 to 25 degrees above normal; on Oct. 4 the city hit 105°F.
• —Nov. 7–9: weak Santa Anas brought coast highs of 80 to 86°F and inland valleys near 90.

Other reasons it can feel hot

In late summer, warm ocean water and humid air from the south can make even onshore days sticky, which is why September often feels worse than July. And if you're inland, it's simply farther from the cooling effect of the ocean: El Cajon can be 15 degrees warmer than Ocean Beach on an ordinary day. See why it's hotter inland than at the beach.

Many coastal homes have no air conditioning. On hot days, county libraries and other public buildings serve as cool zones, and the beach really is cooler than the valleys even when the coast is warm.