As an extensive low pressure system moves from the central US toward the Northeast, more than 20 million people are under alerts for coastal flooding, CNN reports.

Some of those in the area of possible impact include residents of Baltimore and Washington, DC. 

A representative of the National Weather Service (NWS) in Sterling, Virginia says this may be one of the worst tidal flooding events that's occurred in the last two decades, for a number of locations within the Chesapeake Bay watershed.

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

The last time the area was hit with such severe weather was in 2003, when Hurricane Isabel inundated the area with 6.2 feet of water. 

During this current storm, flooding is expected to peak Friday and linger through Saturday; the event may result in two to four feet of coastal flooding.

While this doesn't quite surpass the height of Hurricane Isabel's floodwaters, it's close enough, and the Chesapeake Bay area in Maryland may see even higher water.  

The river gauge for Chesapeake Bay at Cambridge is forecast to reach over 5 feet, which would be the second highest tide on record.

Experts are also keeping an eye on the waters at St George Creek at Straits Point, where the current forecast calls for a maximum height of 5.2 feet, and the Annapolis City Dock, where some say the water could reach a height of 5.1 feet.

Should the waters at the Annapolis City Dock hit 5 feet, significant flooding would occur along the lower Tidal Potomac and adjacent tidal tributaries.

In addition to the possibility of dangerous flooding, high wind warnings and wind advisories are also in effect for several counties with wind gusts expected to reach as high as 60 mph.