What to Know
- Remnant moisture from Tropical Storm Mario will move through Southern California on Thursday.
- A flood watch will be in effect from 5 a.m. Thursday for a wide stretch of the region, including Altadena and Pacific Palisades, which were devastated by the wildfires.
- Temperatures will drop significantly from Wednesday’s highs, but humidity will remain elevated, as high as 69% in Los Angeles County.
- Some areas can expect up to 2 inches of rain.
Showers and thunderstorms are expected to hit Southern California Thursday morning, bringing the chance of flash flooding across Los Angeles County.
Rain and thunderstorms begin overnight and continue all day Thursday. While storms can pop up just about anywhere in SoCal, the bulk of the moisture sticks inland and over the mountains and deserts through the afternoon and evening on Thursday, according to NBCLA Meteorologist Shanna Mendiola.
A flood watch is in effect for most of the mountains from San Luis Obispo to Los Angeles County beginning Thursday morning, according to the National Weather Service. Burn scar areas in Altadena and Pacific Palisades are part of the flood watch advisory.
The region is in the grip of a muggy heat wave that will yield to monsoonal moisture early Thursday, according to the National Weather Service.
Temperatures will drop significantly from Wednesday’s highs, but humidity will remain elevated, as high as 69% in Los Angeles County, forecasters said.
Remnants of Tropical Storm Mario could dump up to 2 inches of rain in some areas. A flood watch will be in effect from 5 a.m. Thursday for a wide stretch of the region, including Pacific Palisades, which was devastated by January’s wildfire.
“Localized flooding in roadways & low areas is possible & there is a 20% chc for minor debris flows from recent burn scars, and 15% for more significant debris flows,” the NWS’ Los Angeles office posted Wednesday on X. “The greatest concern is for the Eaton, Palisades, Bridge, Post, Franklin, Hurst, Hughes and Lake.”
Heads Up: A flood watch is in effect for most of the mountains from San Luis Obispo to LA Co from early Thur morning – Thur night. This corresponds with a broad swath of rain expected to arrive during the overnight hours. Stay tuned for updates. #socal #cawx #CArain pic.twitter.com/P8MU0wevtV
— NWS Los Angeles (@NWSLosAngeles) September 17, 2025
Los Angeles Mayor Karen Bass’ office said the city was monitoring the forecast, and coordinating with the Emergency Management Department, the fire and police departments, the recreation and parks department and the Los Angeles Department of Water and Power to ensure all are ready to respond as needed.
“It’s important to understand that this pattern is very different from a traditional winter storm and even from our typical summer afternoon convection,” the NWS said. “While most areas will get at least some rain, some areas may get little to none, while others just a short distance away could have flooding.”
Highs are expected to reach 81 in downtown Los Angeles on Thursday and 80 on Friday, with similar numbers in most inland county areas.
Overnight lows will be warmer than normal into early next week as the moisture aloft will trap a lot of the heat from the daytime. Overnight temperatures in the upper 60s and low 70s are expected to be the norm in the inland areas.
The high humidity levels will continue into early next week, with a slight chance of showers as additional moisture from the south arrives.
Source: NBC Los Angeles
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