Tropical moisture brought September rains and thunderstorms to Southern California Thursday, making for treacherous driving and fueling fears of flash floods and mudslides in recently burned areas.

The first rains of the fall caused the usual slicking of roads and several crashes followed on Los Angeles area freeways.

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 was in effect as of 5 a.m. Thursday for a wide stretch of the region, including Pacif

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