Photo by Rick Geary

You can take the life vests off the kiddies.

Dear Mr. Alice: When will the highest of high tides be? This enclosed article says March 8, 1993, and that it will not be matched for 1400 years. The high tide in San Diego on that day is listed as a 6.4 — not that high. Are those numbers not completely accurate? Can a 6.4 high tide come farther up the beach, at a certain time of year, than a 7.0? — Jorge, La Jolla

You can take the life vests off the kiddies, Jorge, and cancel that getaway to the Lagunas on the 7th. As your reading of the local tide table indicates, the legendary 1400-year inundation isn’t heading our way. Or anybody’s else’s way, for that matter. Your 1983 newspaper article, clipped from what appears to be the Los Angeles Times, was part of a flurry of publicity given to some ideas about catastrophic coastal flooding that have proven to be, shall we say, all wet. It was another illustration of the old notion that if you chum the intellectual waters with enough charts and calculations, someone will take the bait.

In 1978 the generally respectable Naval Oceanic and Atmospheric Administration published a book of research by one of its employees, Fergus Wood’s Strategic Role of Perigean Spring Tides in Nautical History and North American Coastal Flooding, 1635 to 1976. If the name wasn’t impressive enough to quell any media skepticism, then the book’s size and weight were — 538 pages, 8-1/2 by 11. Aside from the very detailed 350-year survey of storm- and flood-tide-related disasters, the book included a veritable tsunami of numbers, charts, graphs, and calculations based on astronomical data. According to the author, this all added up to predict, among many other things, a doozy of a coastline inundation on March 8, 1993, that would not be matched again for 1400 years.

When the West Coast was hit by severe storms and flooding in the winter of ’83. I guess that primed the public to hear more bad news, tide-wise. The media turned for predictions to Wood and other scientists who subscribed to his theories. The result was the aforementioned “March 8, 1993” scare, which appeared in the New York Times, Wall Street Journal, and a few other publications. Scientific challenges to Woods’s theories got much less ink.

So on March 8, we won’t be jet-skiing off the coast of Julian, but tides will be slightly higher than normal because of an unusual moon thing. The moon’s orbit varies from circular to elliptical; when it’s an ellipse, the path brings the moon to its closest point to Earth (216,000 miles). In the early morning hours of March 8, the moon’s orbit will beat maximum eccentricity and, coincidentally, the moon will be full. Both conditions will produce a stronger than usual effect on tides, though it will be more noticeable at the equator than on the West Coast of the U.S.

As for your last question, the +6.4 high tide is the depth of the water (6.4 feet above the mean low water mark) at a specific location. The same general forces that create a 6.4-foot tide at, say, La Jolla Shores might produce a 6.8 in San Diego Bay, and a 6.2 someplace else. Local topography is a major determiner of tide levels at a given place.