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Worst coastal flooding in over a decade possible in the Mid-Atlantic and Northeast

In some places, high water levels could rival Hurricanes Isabel and Superstorm Sandy.
NYC Faces Flash Flood Watch, Travel Advisory As Storm Moves In
New York City commuters face a blustery, soaked-to-the-skin trek to work as a powerful coastal storm unwinds across the Northeast.Jeenah Moon / Bloomberg via Getty Images

It will be a nasty end to the week for millions with heavy rain and wind stretching from the Ohio Valley and Mid-Atlantic and up into the Northeast and eventually New England.

The greatest impact may not be the flooding rainfall like the last few storms, but instead the coastal flood threat, which in some places could see the most significant tidal flood event since Hurricane Isabel in 2003.

On Friday morning, 18 million people were under coastal flood alerts, where up to 3 feet of inundation could be possible especially at high tide times. Meanwhile, 21 million people were under wind alerts across the Mid-Atlantic to Northeast where winds could gust up to 50 mph especially along the coast and 10 million people were under flood watches where up to 2 to 4 inches of rain could fall over saturated ground.

Throughout the day on Friday, rain will be heavy at times, leading to ponding on the roadways and isolated flash flooding, especially in cities.

The greatest flood threat, however, will come from coastal flooding. Strong onshore winds combined with high water levels leftover from the nor’easter earlier in the week could lead to one of the biggest tidal floods in the past 10 to 20 years, and worst since Isabel in 2003.

Possible impacts from the coastal flooding will be impassable roads, water into low shoreline homes and buildings and flooded marinas. This threat will last through the high tide cycles of Saturday afternoon.

Of particular concern are areas along the Chesapeake Bay, Delaware Bay, Delaware River and Potomac River where dozens of river gauges along those waterways were forecast to reach moderate to major flood stage.

One of those areas, the Delaware Bay at Reedy Point, was forecast to break the all-time highest water level ever recorded on the Delaware Bay. According to the meteorologist Bill Karins, if the forecast comes to fruition that will be higher than Hurricane Sandy nine years ago to the day and higher than the historic nor'easter in April 2011.

Parts of the Washington, Baltimore and Philadelphia metro areas could experience tidal flooding. Annapolis, Maryland, already experienced inundation Friday morning.

By Saturday, the heaviest rain is expected to fall across northern New England, but rain showers and gusty winds will linger across the Mid-Atlantic and Northeast through Saturday night.

Region-wide 1 to 3 inches of rain will fall through Saturday night, with locally higher amounts up to 4 inches.

The good news is the storm system will exit off the coast just in time to provide dry skies for trick-or-treating.