A coastal flood advisory came into effect at 5am on Sunday at Southland beaches, with forecasters warning of possible record high tides.
High tides of between 7.5 and 8 feet are expected during the morning hours from Sunday through Thursday over all coastal areas, according to the National Weather Service.
Forecasters said Monday through Wednesday's tides could challenge the current record of 7.93 feet, set in San Pedro on 10 January 2005. Records go back to 1924.
The advisory runs from 5am Sunday to 1pm Thursday and applies to Los Angeles and Orange County beaches. The weather service said there was a moderate rip current risk during the advisory period.
The service also set out what it expects to happen. "Minor coastal flooding is likely purely based on the high tides. While these tides might be the highest of all-time, similar extreme tides in the past tell us that coastal communities should expect shallow flooding of harbor walkways, beach parking lots and bike paths," it said.
Warmer weather is expected to prevail in the Southland early this week, with daytime highs mostly in the mid- to upper 70s. Cooler conditions follow by midweek, with a growing potential for a significant storm system towards the end of the week.
"The pattern will start to change around Thursday, with onshore flow returning, temperatures dropping, and low pressure forming over the West Coast. This will open the storm window over California, with a growing chance of a significant storm impacting the local area as early as Friday but more so for the weekend," the weather service said.
Forecasters said there is a 90 per cent chance of rain at some point in the 30 October to 2 November window, with Halloween activities likely to be affected.
The sentence worth rereading is the one describing the outcome. These tides might be the highest of all time, and on the evidence of similar extreme tides in the past, coastal communities should expect shallow flooding of harbour walkways, beach parking lots and bike paths.
The record is therefore being contested in a category whose prize is a wet car park. A 102-year high-water mark would have to exceed 7.93 feet, and would then do, within an inch or two, exactly what 7.93 feet did in 2005.
The structure of the advisory gives the rest of it away. It runs for four and a half days and names the mornings on which the record may fall, which makes this the rarest class of record: one with a published timetable, available in advance to anyone who can read a tide table.
San Pedro's mark has stood for 21 years and may be retired on a Tuesday morning, between 5am and the end of the advisory, by a sea that has been scheduled to do it. The Department of Unnecessary Research notes that nothing at the harbour will distinguish the all-time record from the previous one, and has asked the weather service whether a record whose effects are indistinguishable from its predecessor's can be said to have been broken.
The question will not hold up the water. Some time this week the Pacific will stand higher against the Los Angeles shoreline than it has at any point in 102 years of measurement, and the bike path will be shut for the morning.