Soundside Surprises: What’s with the no-advance-warning Pamlico Sound flooding?

Twice in November, Hatteras and Ocracoke islands had coastal flooding from the Pamlico Sound.

And both events caught our local National Weather Service forecasters in Newport, N.C., by surprise.

Now it seems possible that both of the flood tides might be connected to higher than normal tides that have been observed up and down the East Coast since early June.

The first tidal flooding from the sound on Hatteras and Ocracoke came on Friday, Nov. 13, during the storm that is now being called Nor?Ida.  

The remnants of Hurricane Ida, which came ashore on the Gulf Coast of Alabama, made their way across the southeast and back into the Atlantic, forming a northeaster that hung for days off the Outer Banks, battering the islands, seriously damaging parts of Highway 12 in north Rodanthe, and taking a toll on houses and other structures in South Nags Head, Rodanthe, and Buxton.

From Friday morning into Sunday morning, Nov. 15, there was tidal flooding from Frisco to Ocracoke.

The flooding in Frisco was not too serious, but in parts of Hatteras and Ocracoke the water rose to a foot to a foot and a half along parts of Highway 12 in the villages. Then, two weeks later, on Friday, Nov. 27, the islands saw tidal flooding again with the passage of a cold front and moderate winds that blew a steady 25 to 30 mph with gusts up to 45.

On that morning, the tide started coming up just before dawn, surged for several hours, and quickly receded.

Hatteras and Ocracoke villages did not have as much tide as on Nov. 13.  Frisco had much more tide, and there was serious tide, up to a foot in places, in Avon and Salvo, where there had been no flooding during Nor?Ida ? at least not from the soundside.

?We weren?t expecting that,? NWS meteorologist Scott Kennedy said by phone from Newport the week after the northeaster.

?The north wind pushed the water into Hatteras and Ocracoke,? he said, adding that the moderate winds were not strong enough to make forecasters think that there would be soundside flooding.

However, he said after the storm that the flooding was probably caused by a combination of the tremendous amounts of rainfall in eastern North Carolina during the northeaster ? rainfall that eventually drained into the sound ? the heavy tides and swell from the northeast wind that limited the ability of the sound to drain through the inlets into the ocean. The storm also came at a time of astronomically higher than normal tides.

That was a plausible explanation.

Then there was Friday morning, Nov. 27.

The tides in the sounds and its creeks and marshes had never receded very much after the northeaster. A cold front moved across the area in the early morning hours of Friday, the wind shifted to northwest, and picked up ? to maybe a steady 25 or 30 with gusts up to 45.

Nothing that the Weather Service or many islanders would expect to bring the kind of flooding that happened in those early morning hours.

So it was a surprise when many of my neighbors and visitors to the island over Thanksgiving weekend woke up at daylight to water, water everywhere.

Folks were quickly moving vehicles to higher ground, people who had to go to work had trouble getting there, and locals and visitors hoping to hit the Black Friday sales on the northern beaches found their path blocked all the way up and down the islands by sound tide.  Many drove through it, and some of them wished they had not.

The National Weather Service did not issue a coastal flood advisory until about 3 a.m. and changed that to a warning about 6 a.m. as forecasters began getting reports of tide on the highway and through the villages of Hatteras and Ocracoke.

Robert Frederick, a forecaster in Newport on Friday, Nov. 27, said that the Weather Service has models on which it relies for coastal flooding from the Pamlico Sound ? how hard it has to blow from which direction, etc., to send the water up.

?These last two events never followed that,? Frederick said.

The tide, he said, stayed a foot or more above normal after the northeaster.

?Since the northeaster, the tide has been running about a foot above normal, and that?s what we?ve been experiencing,? added meteorologist Brian Cullen.

Cullen said the heavy rainfall of two weeks earlier could not entirely account for the higher than normal tides. And he referenced newspaper articles, based on National Oceanic and Atmospheric Administration media releases, about tides that ran higher than normal from Maine to Florida over the summer.

In an Aug. 31 media release, NOAA said a new technical report attributed higher than normal sea levels along the Eastern Seaboard in June and July to ?persistent winds? and ?a weakened current? in the mid-Atlantic.

?After observing water levels six inches to two feet higher than originally predicted, NOAA scientists began analyzing data from select tide stations and buoys from Maine to Florida and found that a weakening of the Florida Current Transport?an oceanic current that feeds into the Gulf Stream?in addition to steady and persistent Northeast winds, contributed to this anomaly,? NOAA said in the release.

?The ocean is dynamic and it?s not uncommon to have anomalies,? said Mike Szabados, director of NOAA?s Center for Operational Oceanographic Products and Services. ?What made this event unique was its breadth, intensity, and duration.?

NOAA said the high tides over the summer were ?amplified by the occurrence of a perigean-spring tide, the natural timing of the season and month when the moon is closest to the Earth and its gravitational pull heightens the elevation of the water.?

The combined effects of this tide with the sea level anomaly produced minor flooding on the coast, the report concluded.

Other scientists have different theories on the higher than normal tides, but they all seem to agree that they are not caused by global warming and sea level rise, since they happened quickly and not slowly over time.

 ?The report is a good first assessment,? said NOAA oceanographer William Sweet. ?However, NOAA, with our academic partners, should continue to investigate the broader causes behind the event. Further analysis is needed to fully understand what is driving the patterns we observed.?

The full report, ?Elevated East Coast Sea Level Anomaly: June-July 2009,? is available online.

Back on Hatteras and Ocracoke, Ernie Foster, Hatteras village charter boat captain, said he thought tides were a little lower than normal in the Pamlico Sound over the summer.

He said he began noticing the higher than normal levels in late August.

He said through the fall, the ?morning coffee guys? ? the watermen who gather at the marinas early each day ? started talking about the abnormally high tides.

Foster said that on the morning of the start of the soundside flooding in the northeaster on Nov. 13, the tides were about 1.5 feet above normal at Hatteras Harbor.

Given the fact that the wind was barely blowing, he said, the flooding ?never should have happened.?

?The most interesting thing to me,? Foster added, ?is how little scientists know about what?s going on ? not that they haven?t been trying to find out.?

Meanwhile, the meteorologists in Newport said we could have another surprise sound flooding event if the Pamlico Sound tide stays higher than normal.

There are no tide gauges on Hatteras and Ocracoke to guide them about how high the tides are running, so they say they are depending on news bulletins from those of us on the ground to alert them to the flooding.

Scott Kennedy said he first noticed the soundside flooding during the northeaster on Saturday morning, Nov. 14, when he saw photos from readers on The Island Free Press Web site.

There were no flood warnings earlier, he said, because ?we did not get the information into us in a timely manner.?

The Weather Service was apparently relying on media releases from Dare County Emergency Management and other information from the island during the northeaster.  Although those county bulletins came out two or three times a day, they never mentioned soundside flooding.

So, let?s help out our Weather Service forecasters.  They said they welcome phone calls, and especially photos.

You can reach the National Weather Service meteorologists on duty in Newport by calling 252-223-5122, ext. 7.  Or e-mail them information and photos to wxobs.mhx@noaa.gov

FOR MORE INFORMATION
For more information on the higher than normal tides on the East Coast, go to:

http://www.link757.com/2009/07/higher-tides-affecting-east-coast-especially-midatlantic

http://www.27east.com/story_detail.cfm?id=224470&town=East+Hampton&n=Experts+explain+why+tide+swings+have+been+unusually+high

http://www.noaanews.noaa.gov/stories2009/20090831_tides.html