The coastal flood warning for this coast now runs until 2 a.m. Friday. The National Weather Service in Jacksonville reissued it at 3:33 Tuesday morning. The product carries the action code EXT against event number 0003, which is the service’s notation for extending a warning already running rather than opening a new one.

This issuance describes the hazard as “moderate flooding during times of high tide,” where the issuance the service put out early Monday had read moderate to possibly major. The wording has come back down a step. Nothing in the new product explains the change, and the service is under no obligation to explain one.

Two other products run to the same hour. The High Surf Advisory gives “large breaking waves of 7 to 10 feet,” and the High Rip Current Risk, which the service separates out, runs “through late Thursday night” rather than to Friday morning.

All three of the products name exactly the same ground. The area line on each of them reads Coastal Nassau, Coastal Duval, Coastal Flagler, Northeast Coastal St. Johns and Southeast Coastal St. Johns, and the warning text puts the hazard at “Northeast Florida Beaches.” The flood warning is the one of the three the service files at severity Severe; the surf advisory it files at Minor and the rip current statement at Moderate. Severe is the service’s own word for it.

What the tide table says

High water at the St. Augustine Beach gauge is predicted at 6.49 feet above mean lower low water at 10:10 this morning, 6.36 feet at 11:02 Thursday morning, and 6.14 feet at 11:57 Friday morning. The station’s published offsets are set on the 1983-2001 tidal epoch. On those offsets the three heights are about 3.36, 3.23 and 3.01 feet above NAVD88, which is the datum an elevation certificate is written in. Mean higher high water at that gauge is the average of the daily higher high across the epoch, and it sits 5.14 feet above mean lower low water. All three of this week’s midday highs are better than a foot above that.

The warning ends at 2 a.m. Friday. Friday’s high tide is at 11:57 in the morning, which the table has at 6.14 feet, above mean higher high water and higher than Wednesday night’s high. That gap is about ten hours.

The overnight highs are the smaller ones this week. The table gives 5.04 feet at 10:36 Wednesday night and 4.88 feet at 11:30 Thursday night. Both are below mean higher high water, and both are more than a foot under the midday figure for the same day. The water that closes a road here arrives in the late morning rather than after dark.

These are predicted heights and they do not include whatever the wind is doing, which on this stretch of coast is usually the difference between a forecast height and a flooded street.

What the service says it expects

The impacts paragraph reads that “numerous roads may be closed.” It says “low lying property including homes, businesses, and some critical infrastructure will be inundated,” and that “some shoreline erosion will occur.” The instruction block asks people to “take the necessary actions to protect flood-prone property” and, if travel is required, not to “drive around barricades or through water of unknown depth.”

The product’s expires field reads 5 a.m. Wednesday, which is the hour by which the service has to issue the next one rather than the hour the water goes down.