LA Weather Forecast: Heatwave, Flash Flood Risk & Air Quality Alerts for the Week Ahead

Angelenos are bracing for a one-two punch of extreme heat and rare September rainfall as a late-season tropical system drifts over Southern California. The National Weather Service (NWS) has issued a heat advisory through 7 p.m. for the San Fernando Valley, Santa Monica Mountains and inland Ventura County, warning of temperatures soaring to 100–105 °F accompanied by sticky humidity. Forecasters say the unseasonable heat is only phase one. Moisture pulled northward from the remnants of Tropical Storm Mario is expected to arrive late Wednesday, setting up pockets of heavy downpours on Thursday that could trigger debris flows near recent burn scars and snarl the Thursday morning commute. A second plume of tropical moisture may reload the atmosphere Sunday into Tuesday, raising the probability of additional showers and isolated thunderstorms. Residents should plan their outdoor activities before peak-heat hours, stay hydrated and check on vulnerable neighbors. Cal/OSHA is urging employers to provide shaded breaks and cool drinking water for outdoor workers, while Los Angeles County is opening cooling centers across the San Fernando and San Gabriel valleys. Drivers should keep windshield wipers in good shape and avoid flooded underpasses; just six inches of moving water can stall a sedan. Beachgoers will also contend with elevated surf and dangerous rip currents as the storm energy passes offshore. If the forecast verifies, this week could go down as one of the city’s most dramatic September weather swings in years. Stay tuned to NWS updates and local emergency alerts, and bookmark this page for the latest Los Angeles weather forecast, heat advisory extensions and storm timing updates.