In addition to flooding caused by coastal storms, New York City also experiences flooding from thunderstorms and other intense rainstorms. This is flash flooding.

Flash flooding is the number one cause of deaths associated with thunderstorms, claiming more than 140 lives each year in the United States.

• On July 18, 2012, a cold front approaching from the northwest and nearly parallel to the wind flow aloft triggered training thunderstorms, which produced heavy rainfall and resulted in flash flooding in Queens and Manhattan. Heavy rain caused flooding across the FDR Drive between 34th St. and 96th St. in Manhattan.
• On October 1, 2010, heavy rain and flooding occurred in portions of New York City due to transport of tropical moisture, including the remnants of Tropical Storm Nicole. At Central Park, 3.56 inches of total rainfall was recorded, the FDR Drive was closed northbound at 61st St. in Manhattan due to flooding, and three subway lines were suspended due to flooding.
• On July 29, 2009, a pre-frontal trough caused scattered severe thunderstorms to develop across Southeast New York. Some of the storms produced very heavy rain which led to flash flooding in New York City, and prompted the closure of FDR Drive southbound at 14th St. and Houston St. Three days earlier, on July 26, multiple severe thunderstorms and isolated flash flooding in portions of Southeast New York. FDR Drive was closed at 116th St. due to flooding, and six inches of standing water accumulated at the intersection of W. 46th St. and Broadway.
• On August 15, 2008, an anomolous slow moving upper level low pressure system in combination with a weak surface cold front and local seabreezes triggered thunderstorms producing torrential rainfall, which led to flash flooding in portions of New York City. The torrential rainfall caused a sewer to collapse producing a 6-foot deep sinkhole outside of FDNY ladder company 24 on W. 31st Street in Manhattan. That day, OEM reported that all lanes were flooded on the Henry Hudson Bridge between Manhattan and Bronx.
• On October 11, 2007, flash flooding occurred across parts of the New York City metropolitan area, including the West Side Highway. Rainfall amounts ranged from around 1.25 to just under 4.5 inches, with most locations receiving from 1.5 to 2.75 inches of rain.
• On August 8, 2007, a severe rainstorm accompanied by an EF2 tornado brought three inches of rain in two hours to New York City and flooded streets and subways, shutting down service for several hours.

Flash floods can strike any time with little or no warning. City streets can become rivers in seconds. Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms. Blocked catch basins, storm drains, water main breaks, and sewer lines can also lead to flooding.
Read more about flash flooding causes from the NYC Department of Environmental Protection

Flash Floods and NYC

Much of New York's infrastructure — particularly low-lying and poor drainage areas — cannot cope with rainfall of more than one inch per hour.

National Weather Service Terms

• FLASH FLOOD WATCH: Issued when it is possible rains will cause flash flooding in a specified area.
• FLASH FLOOD WARNING: Issued when flash flooding is occurring or is imminent in a specified area.

Flash Flooding Risks

STREET FLOODING

Significant street flooding can pose risks to both pedestrians and drivers.

• Avoid walking through moving water.
  • Water may be contaminated by oil, gasoline, or raw sewage.
  • Water may be electrically charged from underground or downed power lines. Stay away from downed power lines, and report them to the power company.
• If you have to walk in water, walk where the water is not moving or use a stick to check the firmness of the ground in front of you.
• Do not drive into flooded areas.
  • Six inches of water will reach the bottom of most passenger cars, causing loss of control and possible stalling.
  • A foot of water will float many vehicles.
  • Two feet of rushing water can carry away most vehicles, including sport utility vehicles (SUVs) and pick-ups.
• Stay out of any building if it is surrounded by floodwaters.

SEWER BACK-UPS (SBUs)

One of the causes of flooding is surcharged sewers/sewer back-ups. Sewage is carried in different pipes than those for drinking or washing water. Unless otherwise notified, it is safe to drink tap water in an area with flooding; however, floodwater from SBUs can pose serious health risks.
Watch a simulated SBU
See an illustration of an SBU

Reduce Your Risk

The New York City Department of Environmental Protection (DEP) illustrates how the City's sewer system manages rainwater, and offers residents and business owners methods to reduce flooding:

• Depressed driveway protection: If your property has a driveway that slopes below street level, the City recommends you contact a contractor to help prevent flooding into your basement. Obtain two or three quotes from different contractors before beginning the work, as the job can vary widely in price depending on various field conditions.
• Green spaces, trees, and plants absorb rain water and prevent it from collecting and pooling on concrete surfaces. When possible, plant vegetation and avoid paving over green space. If you identify a good area for a tree in your neighborhood, visit www.milliontreesnyc.org, to request a tree from the New York City Department of Parks and Recreation.
• For additional resources, visit DEP's website.

Cleaning After the Flood

• Dry all areas and items quickly and thoroughly.
• Dryclean or wash and dry all clothing and other home items.Clean floors, furniture, and other surfaces with detergent and water.
• Stay out of deep water. Extensive flooding damage may require clean-up and restoration by professionals.