Now it’s time to endure the consequences of this morning’s “supermoon.” Just in case you have no idea what I mean by “supermoon,” check out Bri’s blog from last night or my blog from yesterday morning. It certainly was beautiful and we got a lot of great pictures. One of the most unique views comes courtesy of dronegenuity.com and it was shot by a drone over Hudson, MA Sunday evening…
But that big, beautiful moon also creates big tides. In this case, the biggest tide of the year, or what is commonly called the “king tide.” The “king tide” is a normal, natural occurrence that results from the gravity of the sun and the moon. In this case, the unusually close pass of the moon right around the time of the full moon, the so called “supermoon,” is the culprit. Boston’s high tide at 11:08 AM Tuesday morning will be about 2.62 ft higher than the average high tide. By a very close margin, that will be the highest high tide in Boston for 2016. Wednesday’s high tide is almost as high at about 2.59 ft higher than average, but officially Tuesday’s midday high tide is the “king” for 2016. Again, that is strictly a result of astronomy and has nothing to do with weather.
(Graph courtesy of NOAA)
Side note…you might be thinking, “is this a new thing.” No. But sea level rise has made the “king tide” more of a nuisance, and therefore more of a news headline in recent years, especially in cities like Miami and Norfolk. In case you are curious, at the current rate, the sea level in Boston is rising at about 1 ft per 100 years. But that could be the subject of a blog all on its own. You can read more about the effect of sea level rise on “king tides” here.
(Graph courtesy of NOAA)
The problem this time around is that this year’s “king tide” also coincides with a storm system that will move up the coast. So in this case, astronomy will get a boost from weather. As far as coastal storms go, this one is nothing special and normally wouldn’t be cause for concern. It will generate onshore winds, but peak wind gusts might just barely reach 40 mph over the Cape and the Islands. That will generate a storm surge of about .5 to maybe 1.0 ft. Normally that’s not a problem, but on top of tides that are already high, that might be just enough for some minor coastal flooding. Fortunately, it looks like the strongest winds and therefore the highest surge will occur much later in the day, closer to low tide. That reduces the risk for what could have been a much more significant event. The other bit of good news is that wave action is not expected to be significant with this storm, and that reduces the risk for beach erosion. Still the National Weather Service is concerned about flooding of vulnerable shore roads and basements in low lying shoreline areas and areas subject to backwater flooding in very high tides. That has prompted them to issue a Coastal Flood Warning for the NH Seacoast and a Coastal Flood Advisory for the east coast of MA.
The National Weather Service highlights low lying areas of Revere, a few wharves along Boston Harbor, Morrissey Boulevard, locations near the mouth of the Neponset River, low lying areas along Quincy Bay, and the parking area off Cole Parkway in Scituate as areas to keep an eye on.
The other bit of good news is the much needed rain. Again, this isn’t a monster storm so we aren’t expecting a drought buster, but a beneficial .5″ seems likely and 1″ isn’t out of the question in some areas. That by itself is not enough to cause flooding. However, the unusually high tides will make it difficult for fresh water to drain into the harbors and bays. So, if there be any bands of heavy rain around the midday high tide, the inability of the fresh water to drain could result in some backwater flooding as well.
The weather clears for Wednesday and we finish the week with some sunny, mild weather. Enjoy it while you can because next week is already trending much cooler. More on that to come!