Meteorologists predict one of the biggest storm surge in the past two decades

(CNN) – More than 20 million people are on alert for coastal flooding, including residents of Baltimore and Washington, as a large and powerful low-pressure system moves northeast from the central United States.

“Right now we expect it to be one of the worst storm surges we’ve had in the last 10 or 20 years for many locations in the Chesapeake Bay Basin,” Chris Strong, National Weather Service (NWS) Alert Coordinating Meteorologist, told CNN. in Sterling, Virginia. “The biggest impact we expect here in the Baltimore / Washington area and along the Chesapeake Bay is tidal flooding.”

The floods are expected to peak on Friday and last through Saturday. During this time, coastal flooding of between 609 and 1,220 millimeters is likely to occur.

The last time conditions were this bad was during Hurricane Isabel in 2003.

During that storm, Fell’s Point in Baltimore, the US Naval Academy, downtown Annapolis, and the Belle View neighborhoods in northern Fairfax County, Virginia, experienced severe flooding from storm surges, according to NOAA.

Although Strong cautions that the flooding with Isabel was several inches higher than forecast for this storm, this will be one of the worst tidal floods since that hurricane in 2003.

The Chesapeake Bay River Marker in Cambridge, Maryland, is forecast to will exceed 1.5 meters. This would make it the second highest tide on record, behind a height of 1.8 meters that was reached in 2003 during Hurricane Isabel.

Another worrying spot is St. George Creek at Straits Point, where the current forecast indicates a maximum height of 1.5 meters, which places it above the threshold of major floods. If it reaches that height, it would break the previous all-time record of 1.4 meters set in 2018.

Only one meter of water is enough, according to historical records, for it to “cover the roads on the island of St. Georges, it is in the courtyards and it approaches the structures”, according to the National Weather Service (NWS).

“Water anomalies are already up to 609 millimeters at Straits Point and increasing, and Annapolis is approaching the minor flood stage even as the astronomical tide turns to low tide,” said the NWS in Baltimore.

As of Thursday afternoon, the crest forecast for the Annapolis City Pier is 1.55 meters. If the water level reaches 1.52 meters, there will be significant and widespread flooding along the lower Potomac and adjacent tidal tributaries. Numerous roads and structures would also be affected.

“At that level of water, the historic Annapolis City Pier will flood and It will look like St. Mark’s Square in Venice when it floods, “says Chad Myers, a CNN meteorologist.

But even if the tide reaches only 1.2 meters, the Annapolis City Pier Boardwalk will be underwater. The water also affects several places near the city dock, including parts of Compromise Street and several streets on the Naval Academy campus.

Yes the water reaches 1.80 meters, major flooding will occur in the Annapolis city dock area and parts of the Naval Academy campus. Many roads and fields tend to flood at this height, and the water seeps into several buildings.

Monitoring High Waters in US Rivers and Streams

This is the flood level that has been recorded on the river and stream gauges in the last day.

“Usually when we have such extreme tidal events, it is usually from hurricanes or tropical events,” Strong said. “This is just low pressure moving, but that strong low pressure is working against the high pressure over New England to our north. That combination is driving the flow east just off the Atlantic Ocean and piling up all that water from the Atlantic Ocean. on the coast and in the Chesapeake Bay. “

High wind advisories and wind advisories are also in effect for several counties as gusts are expected to reach up to 60 miles per hour.

“Damaging winds will knock down trees and power lines,” the warning says. “Widespread power outages are expected. Travel will be difficult, especially for high-profile vehicles.”

One of the biggest tidal flood events of the past 10-20 years (possibly since Hurricane Isabel at some locales), is expected Friday & Saturday. Those along tidal shores should get ready for exceptional tidal inundation! Tidal forecasts here: https://t.co/Q2WdpDGgIJ pic.twitter.com/LQkL80pzQs

– NWS Baltimore-Washington (@NWS_BaltWash) October 28, 2021

It is important to note that for the Chesapeake Bay at the Cambridge location, four of the five tallest ridges on record have occurred since September 2003.

The Chesapeake Bay at Windmill Point has recorded 8 of its 10 highest ridges since September 2006.

“Long-term sea level rise due to rising global and ocean temperatures as a result of climate change makes coastal floods like this occur more frequently, with an increasing impact from higher floods,” says Brandon Miller, CNN meteorologist and leader of climate change coverage.

“Sea level has risen nearly a foot since the early 20th century, raising the baseline from which these floods occur, pushing the annoying flooding from storms that previously only occurred during the stronger storms, like hurricanes. “

– CNN’s Tom Sater contributed to this report.