The coastal flood warning on the ocean side of St. Johns County was due to end at eight o’clock on Monday evening. It now runs to five o’clock on Wednesday morning. The National Weather Service reissued it at 3:47 on Sunday morning for Northeast Coastal St. Johns and Southeast Coastal St. Johns, along with Coastal Nassau, Coastal Duval and Coastal Flagler. Its impact line is the one it carried on Saturday, and according to the service, “numerous roads may be closed” and “low lying property including homes, businesses, and some critical infrastructure will be inundated.”

This is tidal flooding, which is water arriving from the ocean side and standing on the ground until the tide leaves again. It is not rainfall flooding and it is not storm surge. The forecast for Monday carries a 48 percent chance of rain showers, so both kinds of water will be on the same streets. Only one of them leaves when the sky clears.

The warning was extended rather than shortened, and the predictions underneath it, which are published days ahead and carry no weather in them at all, are the reason.

The chart is higher now than it was on Saturday

High tide at St. Augustine Beach is predicted for 8:34 Monday morning at 6.344 feet above mean lower low water, and again for 8:58 Monday evening at 5.249 feet on the same datum. Tuesday’s morning high is predicted for 9:21 at 6.485 feet, which is the highest of the three days, and Wednesday morning’s is 6.487 at 10:10, about forty minutes before the warning expires.

The morning highs at that station have gone up on each of the last four days. Saturday 5.707, Sunday 6.075, Monday 6.344, Tuesday 6.485. Saturday’s was the one the first warning was written over. Each one since has been higher. Monday morning’s prediction sits about six tenths of a foot above it and Tuesday morning’s about eight tenths, both figures being one published prediction subtracted from another.

On the station’s own datums record, published for the 1983 to 2001 tidal epoch, mean higher high water sits 5.14 feet above mean lower low water, which is 8.15 minus 3.01 on station datum. Monday’s morning prediction is about 1.2 feet above the average of the higher high tides and Tuesday’s about 1.3 feet. In NAVD88, which is the datum an elevation certificate uses and therefore the one that means something at a doorstep, mean higher high water here is 2.01 feet, Monday’s morning high converts to about 3.2 feet and Tuesday’s to about 3.4. Those conversions are this paper’s arithmetic off two published numbers and not a figure the agency prints.

A harmonic prediction carries no wind, no rain and no surge in it. It is a floor. Not a forecast. The northeast wind in Monday’s forecast is 24 miles an hour, and everything the warning describes gets added on top of the chart.

Station 8720587 is a prediction station with no instrument in the water, so there is nothing observed at St. Augustine Beach to set against any of this. The nearest gauge that reports sits at Mayport, about thirty miles north and inside a different river. The water there was 69.8 degrees at six minutes past two on Monday morning, which is river water and not ocean water.

What the city has done about Monday

The city posted a notice at 4:12 on Sunday afternoon putting City Hall and 50 Bridge Street on a delayed opening, with all offices opening at noon. The notice gives anticipated weather conditions as the reason, names no department as its author and sets no condition for reopening earlier.

It also says that solid waste collection services may be impacted in areas experiencing flooding, which is the sentence to read twice if the can is already at the curb.

Nothing in the notice mentions the three meetings the city has scheduled in the same building that afternoon. The commission’s shade meeting is noticed for three o’clock, the Community Redevelopment Agency for half past three and the regular commission meeting for five, all after the building opens.

The school district’s front page carried no notice about Monday, and the county’s newest weather item is still the release it put out on Friday afternoon urging residents to avoid flooded roadways and stay out of dangerous surf. Neither body had posted a delay or a closure.

The beach and the water

The high surf advisory runs to two o’clock Wednesday morning and the bulletin puts the breaking waves at 8 to 10 feet. The high rip current risk runs through late Tuesday night. Two more nights of it. The service’s own instruction is that inexperienced swimmers should stay out of the water, and that a swimmer caught in a rip current should relax and float rather than swim against it.

Offshore, two gale warnings are running to different hours. The one covering the water from St. Augustine to Flagler Beach out 20 nautical miles ends at two o’clock Tuesday morning, and the same stretch from 20 to 60 nautical miles runs on to two o’clock Wednesday morning. The nearer water is released a day before the farther water. Monday sits inside both.

On a flooded road the weather service and the county say the same two things, and both are worth the space. Do not drive around a barricade. Do not drive through water of unknown depth.

The regular City Commission meeting is at 5 p.m. in the Alcazar Room, and Ordinance 2026-23, which expands the zone where the city can enforce illegal parking, is on second reading. City Hall opens at noon.