Atlantic Hurricane Outlook and the Threat from Flooding in DC

Today, the National Oceanic and Atmospheric Administration (NOAA) issued its 2019 Atlantic Hurricane Outlook. NOAA predicts a near-normal hurricane season with a range of nine to 15 named storms, of which four to eight could become hurricanes, including two to four major hurricanes (category 3, 4 or 5; with winds of 111 mph or higher). NOAA provides these ranges with a 70% confidence. The hurricane season officially extends from June 1 to November 30.

Flash flooding poses a threat to the District of Columbia during hurricane season. Flash floods, also known as interior floods, occur when heavy rainfall cannot be absorbed by the ground and overwhelms the drainage system. Urban development, weather conditions, local landscape—such as soil, grass, or asphalt—and storm drainage capacity are all factors that contribute to flash flooding, causing rainwater and sewage to flood basements and streets. Flash floods can occur at any time of the year, even when river elevations are normal.

  • The Federal Triangle Flood in 2006 submerged the Internal Revenue Service basement under five feet of water and caused a four-day shutdown of the Federal Triangle metro station.

  • The Bloomingdale Flood in 2012 caused residential basements and streets to flood with sewage from a multi-day rain event. Flooding threats in this area are greatly reduced due to the construction of the First Street Tunnel and the McMillan Stormwater Storage site.

  • The Cleveland Park Metro Station Flood in 2016 closed the station when rainfall amounts exceeded the ability for streets to drain, flooding catch basins. The water overflowed sidewalks and flowed down the station escalators.

DC instituted a mitigation strategy to combat two additional types of flooding—riverine and coastal flooding—through the use of a levee system. The Potomac Park Levee System is operated by the National Park Service, and the Anacostia Levee System is operated by the Department of the Navy.

  • Riverine flooding occurs when heavy rainfall upstream, north and west of DC, increases water levels causing the rivers to overflow their banks.

  • Coastal flooding, or storm surge, can occur when hurricanes drive water and waves from the Atlantic Ocean into the Chesapeake Bay causing the rivers to overflow their banks.

District residents and businesses should check to see if they are in a potential flood zone and can learn how to prepare for hurricanes by visiting the ReadyDC Hurricane page. The map on the following page shows previous locations of interior flooding in DC produced from available data from flood insurance claims, calls for service, and previously flooded areas.

Additional Resources:

Map Source: DC Silver Jackets Interior Flooding Task Group, August 25, 2017

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