"Supermoon" And Possible Storm Create Risk Of New England Coastal Flood

Minor coastal flooding in Gloucester, Mass caused by
a king tide. Photo by Donna Ardizzoni via CBS Boston.  

You've probably heard we're going to get a "supermoon" early next week, in which the full moon will appear in the sky much larger than normal.

The distance between the Earth and the moon varies, and early next week, the moon will be closer to Earth than usual.

 In fact, it will be the closest to us since 1948 and won't come this close again until 2034.

People that have clear skies Tuesday night will have a really, really bright and big moon. It will be quite a show.  The full moon will look 14 percent larger and 30 percent brighter than usual.

In New England, it looks like clouds, as usual, will interfere with the view. Worse, the supermoon and a run-of-the-mill storm along the coast could cause some coastal flooding.

The moon is the force that exerts its influence on the tides. Since the moon is closer than usual, it can make higher tides. Coastal areas can expect what are known as "King Tides" that are higher than normal, even if there is no storms around to cause any kind of extra high water levels.

Since sea levels have risen, especially along the East Coast, there's a good chance of some coastal flooding even where there's no storm, such as near Miami, Norfolk and other low lying areas in the Southeast.

The Miami Herald says the expected high tides come just a month after a similar flooding episodes, and flooding from tides has increased markedly in recent years. This will be just another bad example of rising sea levels there.

Up in New England, we're expecting a nor'easter. By the standards of the region, this one will be lame. Just a slug of rain and some fairly gusty coastal winds. Definitely not a big deal.

At least not normally. But as meteorologist Eric Fisher at CBS Boston notes, nor'easters do cause an east wind in New England as they approach. The King Tides  combined with the east winds pushing water onshore could easily cause some pretty good flooding along the coast.

This definitely WON'T  be a mega disaster like Superstorm Sandy or the Perfect Storm by any means.   But if you have oceanfront property in New England, be prepared for flooded roads, beach erosion and maybe some property damage.

The Supermoon strikes again!

"King Tides" Submerged Some U.S. Coastal Areas Yesterday

Tuesday's King Tide swamping Charleston, South
Carolina Tuesday. Photo from WCIV.  

So called "King Tides" gave some U.S. coastal areas - especially around South Carolina - more than they bargained for on Tuesday.

Tides reached near record highs in the southeastern United States, despite the absense of any storms. Usually, tides that come close to record heights come during hurricanes or other severe coastal storms as hurricane winds push a storm surge inland.

This time, no storms. And hate to say it, but climate change had a role in Tuesday's coastal flooding.

Some perspective:

Around the time of the full "supermoon" in the autumn, when the moon is a little closer to the Earth than usual, tides are higher than normal. This is nothing new.

Making it a little worse, winds were from the east along the southern Atlantic seaboard, which drove water toward the coast, making the tides a bit higher than they normally would. Again, this is fairly normal and has happened before. It was just bad luck that the wind was from the east, rather than the west, during this extra high tide.

Had climate change not been around, this would have been a high tide with some coastal flooding but the flooding would not have been too extensive.

Global warming has driven sea levels up by, on average 8 inches since the late 1880s. It's worse along the U.S. East Coast for reasons I'll explain below.

Tides just several inches deeper than in the past don't seem like much, but in flat coastal areas like those around South Carolina, southeastern Virginia or Louisiana, a few extra inches of ocean water can go surprisingly far inland and cause a lot of flooding. The land just doesn't increase in elevation much as you go inland from the beaches.

Making matters worse along the East Coast is that a massive Atlantic Ocean current heading northeastward away from the United States has slowed. That current tends to draw water away from the East Coast.

With the current slowing, less water flows away, so it collects near North America more. Again, we're only talking about a few extra inches of water, but as noted it adds up.

The result, was Tuesday's King Tides, that scored in the Top 10 highest on record in some locations. This is really odd, because as I said, there were no hurricanes around to create a storm surge. Most of big memorable tidal floods are associated with hurricanes.

As Washington Post's Capital Weather Gang notes, "Seemingly overnight, spurred by sea level rise, we've entered an era where king tides compete with hurricanes in the water level record books."

Tuesday's high tide in Charleston, South Carolina peaked at 8.69 feet. That was short of the record high of 12.56 during the epic Hurricane Hugo in 1989, but still high enough to be in the top 5 biggest tides on record for Charleston.

The high tide Tuesday at Savannah, Georgia reache 10.43 feet, the third highest on record. Only two high tides there were slightly higher - those during hurricanes in 1940 and 1947.

Flooding was reported in other areas besides South Carolina and Georgia. Some water invaded Miami Beach, and minor flooding was reported near New Orleans.

This type of non-storm coastal flooding is going to keep getting worse.

Already, a NOAA study has concluded that "nuisance flooding," the type that shuts down very low lying roads and sneaks into parking lots, streets, basements and storm drains, has gone up between 300 and 925 percent along all three U.S. coasts since the 1960s.

Annapolis and Baltimore, Maryland have had the biggest increase in these nuisance tidal floods. The NOAA report says this problem will keep getting worse and worse as sea levels increase.

This can't be good for coastal residents.

Here's how the Miami Herald described Fort Lauderdale on Tuesday:

"Just east of the Intracoastal Waterway in Fort Lauderdale, even before the highest tides, seawater flooded the street outside Shooters Restaurant and lapped at sidewalks.

'I love everything about the neighborhood and the location and the restaurants nearby, but it seems to be getting worse,' said Robert Owen, who purchased his condominium at the nearby Tides at Bridgeside Square about seven years ago. 'It can't be good for property values.'"

No, it can't Mr. Owen! And as the high tides worsen and become more frequent along the coasts, this is going to be a nightmare for insurers, and low lying towns who face expensive work to hold back the tides, plus lower tax revenue from lower property values or people just moving away from the enroaching water.

Meanwhile, another round of King Tides is expected this morning. The tides shouldn't be as bad starting Thursday.