Reading the Tide Charts

For instance, the tide chart below from 2017 shows our region's normal cycle of two high tides and two low tides a day. And each month we get higher high tides on the full and new moon, also called "spring tides," when the celestial bodies align as shown in the first picture above. Each fall the tide cycles produce the "King Tides," when the celestial alignment occurs and the moon is closest to the earth.

The 2017 chart shows a relatively normal high tide in the red circle to the right and the highest tide of the year on our Catch the King Mapping Day in the circle on the left. The numbers are the height of the water above Mean Lower Low Water and, in the example above, the November 5 tide was forecast to be about 10 inches higher than normal. With no wind, we had expected minor flooding in the lowest lying parts of our region.

In our region, the wind plays a major part in our water levels, in addition to the daily, monthly, and yearly tides. Without going into too much geeky detail, we have a very rare shoreline with rivers that run south-to-north. (That shoreline is the southern rim of the largest meteor impact crater in the US, a big bang that happened 56 million years ago!) And these rivers are not white-water rivers with a lot of downhill flow - they are flat estuaries with flows that winds can push around. So, when we get a wind from the north, blowing into the mouths of the rivers, the water starts stacking up. Conversely, when we get a wind from the south, the water flows out into the Chesapeake Bay and our flooding is minimal (though with a south wind Back Bay will start flooding, but that is another story).

This means that on top of the daily, monthly, and yearly tide cycles we also have to factor in the wind. Here's an example of how that works. In this Weather Underground screen shot from October 2016, look at the line of arrows at the bottom, showing the wind speed and direction.

Starting on October 8, 2016, (red circle), the wind shifted out of the N/NE at 20+ miles per hour and started pushing water upstream on our slow-flowing, north facing rivers. Even worse, it kept going for the next few days. This started to cause flooding - as shown in the chart below from the tide gauge at Sewells Point at Naval Station Norfolk. By high tide on the second morning, the tide was 4 feet above mean sea level.

To paraphrase Burt in "Mary Poppins"

Winds in the [nor]east, mist coming in,

Like somethin' is brewin' and bout to begin.

Can't put me finger on what lies in store,

But I fear what's to happen all happened before.

Sure enough, this wind from the nor'east produced nuisance flooding across the region. In Norfolk, it looked like this on October 9, 2016.