Flood Watch in effect as Tropical Storm Kay approaches from Baja California

As Tropical Storm Kay off the coast of Baja California is helping to end the punishing heat wave broiling Southern California, the National Weather Service issued a Flood Watch for the region. 

The Flood Watch is in effect from 11 p.m. Friday through Saturday evening for Antelope Valley, the Los Angeles County Mountains, and the Ventura County Mountains.

Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations.

Kay pushed clouds and some rain into Southern California, but it's unclear how big the storm's impact will be because it's expected to weaken as it moves north.

Showers and thunderstorms with periods of heavy rain at times will increase the risk of flooding, especially in the mountains. The heaviest rain is expected to occur late Friday evening through Saturday evening.

"Moisture from Kay will move into the area Friday and linger through Saturday," according to the NWS. "Showers and thunderstorms with periods of heavy rain at times will increase the risk of flooding, especially in the mountains. The heaviest rain is expected to occur late tonight through Saturday evening."

Forecasters said the rain could lead to excessive runoff resulting in "flooding of rivers, creeks, streams and other low-lying and flood-prone locations."

Kay had been categorized as a hurricane, but it weakened as it made landfall Thursday night, then began shifting to the northwest over the ocean. But Kay was still packing a punch, promising to bring widespread rain across the region.

The cloud cover from the storm was helping to trap warm air in the region, meaning continued hot weather on Friday, despite some overcast conditions, along with increased humidity. Excessive heat warnings will remain in effect for most of the Southland until 8 p.m. Friday. Then the rain will move in.

"Rainfall amounts should generally range between a quarter to half inch for the coast, a third to two-thirds of an inch for the valleys, and a half to one-and-one-half for the mountains," according to the NWS. "For the Antelope Valley, generally a third to two-thirds of an inch is expected for the storm. Locally higher amounts could develop, especially with any thunderstorms. Heavy downpours are possible across the mountains and desert where terrain will cause orographic effects that could increase rainfall rates."