They’re back. Those big tides we saw for several months last fall are returning this week. Astronomically high tides are nothing new; they have been occurring for millennia. Recently, these big tides have been branded as “king tides” because they are some of the greatest tides of the year. As the Moon orbits the Earth, its effect on our tides varies daily, weekly and monthly. Every month of the year has a maximum tide cycle, but during some months these tides are higher than others.

Tides will reach over 11 feet this week in Portland Harbor.

This week, the highest tide will happen on Thursday and Friday, but Tuesday and Wednesday’s tides will also be very large. This, combined with a nor’easter in the same time period, will bring an increased chance of shore road flooding.

This isn’t going to be a major flood, but some of those vulnerable roads will see the water cover them and I expect some road closures as well. This is the type of situation where Commercial Street can get a bit of water on it, but it won’t be major. The continued easterly wind will pile up the water against the shoreline Tuesday and Wednesday. This is also the time when flooding will be most prevalent. The storm may also be accompanied by minor beach erosion.

Easterly winds will bring some minor coastal flooding Tuesday night and perhaps early Wednesday at high tide.

King tides are useful for another purpose. These highest tides give us a window into the future, as climate scientists estimate our tides will be 1 to 2 feet higher by the beginning of the next century. While 12-foot tides are the exception today, as sea levels rise, they could become more routine.

A king tide cycle combined with a storm is what urban planners of the future need to worry about. Imagine a winter coastal storm and astronomical high tides. If the storm remained stalled for days and you had big tides, coastal flooding would reach catastrophic levels. This is precisely what happened in the blizzard of 1978. That storm took down the Old Orchard Beach pier and there’s no reason to think that type of damage couldn’t happen again.

You can follow Dave Epstein on Twitter @growingwisdom