South Bay residents planning Halloween weekend outdoors should prepare for rain, with a storm system expected to arrive as early as Friday, Oct. 30, and last through Sunday, Nov. 1.

The National Weather Service Los Angeles/Oxnard office forecasts about an inch of rain across much of the Los Angeles area, with higher totals possible in foothill and coastal slope areas. There is a 20% to 30% chance some areas could receive about twice that amount, according to Patch, which first reported the forecast details.

NWS forecasters wrote that they have "very high confidence that it will rain during the weekend, but low confidence on onset timing and peak timing." The agency's Oct. 27 forecast discussion described models trending toward a weaker system that would deliver what forecasters called a beneficial rain.

Highs are expected to stay in the mid- to upper 60s through the weekend. Gusty winds are forecast for mountain and desert areas.

If rain falls on Saturday, Oct. 31, it would be the first Halloween rain in Los Angeles since 2014, KTLA reported.

The storm arrives on top of an already active coastal flooding situation.

On Oct. 26, a record high tide of 8.02 feet was recorded at San Pedro, breaking the previous record of 7.93 feet set Jan. 10, 2005, according to the NWS. A coastal flood advisory remains in effect for Los Angeles County beaches through 1 p.m. Thursday, Oct. 29. Forecasters warned of possible shoreline erosion and seawater flooding of harbor walkways, beach parking lots and bike paths.

In Redondo Beach, the high tides have already caused damage. Seawater surged onto the International Boardwalk on Tuesday, Oct. 27, flooding businesses along the waterfront, Patch reported. Project Barley Taps and Grill, at 136 International Boardwalk, stayed open despite several inches of water, with sandbags lining its entrance.

Owner Brent Reger told KTLA the water receded by Tuesday afternoon but the bar's flooring was ruined. Reger has spent months urging Redondo Beach City Council members to replace a wooden retaining wall along the boardwalk with a concrete structure, according to Patch. He said he has been told the issue comes down to funding.

Redondo Beach's capital improvement budget for fiscal years 2023-28 included $950,000 for Basin 3 Seawall Improvements to prevent flooding of boardwalk businesses during high tides and storm surges. Construction was listed for fiscal year 2024-25. Whether that work has been completed is unclear.

For families heading out to trick-or-treat, Dr. Kiran Masood, a UCLA Health pediatrician, warned that rainy conditions reduce visibility and create slippery sidewalks, according to Patch. Masood recommended costumes with bright colors, reflective materials or glow sticks and advised against allowing children to ride e-bikes or e-scooters on Halloween night.

The NWS forecast is expected to come into sharper focus over the next few days as the storm approaches the California coast.