A major storm that broke through the mid-Atlantic to parts of the northeast caused major flooding on Friday and is expected to bring them over the weekend, the National Weather Service said.
Heavy rain during high tide could cause “astronomical waves” of ocean water, said Matt Doody, a national weather service forecaster at the agency’s eastern regional operations center in the Czech Republic, NY.
Maryland, including Baltimore, could experience some of the largest tidal floods in nearly two decades, the weather service said, adding that residents should be prepared for “extreme tidal floods.” Some regions could experience more floods than in 2003, when The Mid-Atlantic was flooded by Hurricane Isabel.
The storm system could also bring the highest water level ever observed in Delaware and Chesapeake Bays, Mr Doody said. That’s why this storm is so prone to flooding, that’s how slow it moves, he said.
Forecasters in the Chesapeake and Delaware Bay areas said water level records may vary from area to area, but added that the records were set by hurricanes or other so-called storms such as Hurricanes Sandy, Ida and Isabel.
An unnamed storm on Friday caused coastal flooding and warnings of heavy rain from Virginia to parts of New Jersey. Warnings of excessive rainfall on Saturday were issued for Pennsylvania, Washington, DC, West Virginia and much of Maryland.
Maryland Gov. Larry Hogan has declared a state of emergency for Baltimore and several counties, saying the storm could be “much more serious” than previous floods.
The governor’s office said the state had closed several campsites and evacuated campers. It added that Maryland State Police responded to 119 traffic accidents, 16 “roadside hazards” and 27 disabled or unsupervised vehicles.
The rain in the Baltimore and Washington area has “subsided” since Friday around 8 p.m., said Ray Martin, a meteorologist at the National Weather Service. However, he added that “the tidal floods are quite severe and this will continue at least until tonight and until tomorrow.”
The rain is expected to spread northeast to New England on Saturday afternoon, and in some places the risk of two to four inches of rain is low, meteorologists said.
“Floods can become severe enough to cause some structural damage, along with widespread flooding of roads near tidal waterways,” national weather service he said.
Delaware has been preparing for a storm for several days, AJ Schall, the director of the Delaware Emergency Management Agency, he said Friday.
Many coastal parts of the country are regularly prone to slight tidal floods. He said he was concerned that a slow storm could worsen the situation in the floods because it would wet the country between 5pm and 9pm during high tide.
“Where the usual outflow would go, they are now holding back the tide,” Mr. Schall he said.
The water level along the Delaware River could reach 11.5 feet around 10 p.m., according to the National Weather Service meter in Burlington, NJ, near the town where Delaware borders parts of Pennsylvania.
The National Meteorological Service warned that many roads could become impassable and that “some neighborhoods may be isolated” due to the floods.
No roads in Delaware have been closed yet, but officials said they expect some to close later Friday. The districts have been warning residents since Wednesday to move their cars to higher positions, Schall said.
Until the first afternoon tide in Washington, workers at the city’s fish market on Friday had to take a small boat, according to a video on Twitter.
Baltimore Mayor Brandon M. Scott said Friday that the city is already experiencing coastal flooding and asked residents to move their cars higher. The city has begun distribution of sandbags residents on Friday morning.
In Annapolis, Md., The city has already experienced floods in port car parks on Friday as early as 9 p.m. Alexandria, Va., Also distributed sandbags with a limit of five bags per address, according to the city statement.
Floods are a complex phenomenon with many causes, including land development and soil conditions.
While determining all the factors of an individual flood requires extensive scientific analysis, climate change, which is already causing heavier rainfall in many storms, is an increasingly important part of the mix. A warmer atmosphere retains and releases more water, either in the form of rain or a heavy winter blanket of snow.
Between 2000 and 2015, the incidence of high tide floods in the mid-Atlantic doubled from an average of three days a year to six, according to the 2018 NOAA report.
According to the report, floods due to high tides have been steadily increasing in the regions, mostly along the coasts of the Northeast and Southeast Atlantic and the Gulf of Mexico. The report predicted that tides in coastal cities would occur every other day for the next 80 years.