Flash Flood Watch: issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.
Flash Flood Warning: issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Coastal Flood Watch: issued by the National Weather Service when coastal flooding is possible within 12 to 36 hours.
Coastal Flood Warning: issued by the National Weather service when coastal flooding is occurring, imminent, or expected within 12 hours.
Types of Flooding and Causes
Flash flooding is caused by thunderstorms and other intense rainstorms, and is the number one cause of deaths associated with thunderstorms, claiming more than 140 lives each year in the United States.
Coastal flooding occurs when intense, offshore low-pressure systems drive ocean water inland. The water pushed ashore is called storm surge. Coastal flooding levels — categorized as minor, moderate, or major — are calculated based on the amount water rises above the normal tide in a particular area.
Minor flooding is nuisance coastal flooding of locations adjacent to the shore. Minor beach erosion can occur. Minor coastal flooding is not expected to close roads or do cause any major structural damage to homes and other buildings.
Moderate flooding is more substantial coastal flooding, threatening life and property. Some roads may become impassable due to flooding. Moderate beach erosion will occur along with damage to some homes, businesses, and other facilities.
Major flooding is a serious threat to both life and property. Numerous roads will likely become flooded. Many homes and businesses along the coast will receive major damage. People should review safety precautions and prepare to evacuate if necessary. Major beach erosion is also expected.
Tidal flooding occurs when the tide's range is at its highest level (also called a spring tide), but it can also occur with no storm.
Riverine flooding occurs when freshwater rivers and streams overflow their banks.
Blocked catch basins, storm drains, water main breaks, and sewer lines can also lead to flooding. Surcharged sewers/sewer backups (also known as SBU) also can lead to flooding. 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.
Storm surge is a dome of ocean water that is pushed ashore by the oncoming hurricane's winds. A major hurricane could push more than 30 feet of storm surge (the height of a three-story building) into some parts of New York City, and storm surge can travel several miles inland. Storm surge and large battering waves can endanger lives, destroy buildings, erode beaches and dunes, and damage roads and bridges. For more information about storm surge, visit the National Hurricane Center online.
What to Do Before a Flood
Know your flood risk. To learn more about flood zones in New York City, visit www.floodhelpny.org.
Flood zones are used to determine flood insurance requirements. Residents should not use flood zones to determine the need to evacuate. For more information about flood zones, visit www.floodhelpny.org.
Consider getting flood insurance. Protection against loss due to floods is not covered under a homeowner's policy. Contact your property/casualty agent or broker about eligibility for flood insurance. For more information, visit the National Flood Insurance Program online at www.floodsmart.gov.
If you live in a basement apartment, be prepared to move to a higher floor during periods of heavy rain. Be prepared to evacuate if needed.
Make an itemized list of personal property, including furnishings, clothing, and valuables.
Make an emergency plan that includes where you will go if you have to evacuate.
Prepare a Go Bag that you can grab in case you need to leave your home in a hurry.
Learn the safest route from your home or workplace to safe, high ground in case you have to evacuate. This should be part of your household disaster plan.
If you have a disability or access or functional need, make sure your plan addresses how your needs may affect your ability to evacuate, shelter in place, or communicate with emergency workers. Arrange help from family, friends, or service providers if you will need assistance.
If you live in a flood-susceptible area, keep materials, such as sandbags, plywood, plastic sheeting, and lumber, on hand to help protect your home.
Stay informed. Sign up for Notify NYC, the City of New York's official, free emergency communications program. Register for emergency notifications by getting the free Notify NYC mobile application, visiting NYC.gov/notifynyc, contacting 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115) or following @NotifyNYC on Twitter. (Notify NYC messages are available through many formats, including email, text messages, telephone, the Notify NYC website, RSS, Twitter, and American Sign Language videos.)
Take Steps to Reduce Your Risk
The New York City Department of Environmental Protection offers residents and business owners methods to reduce flooding. Learn more
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.
What to Do During a Flood
Listen to local weather forecasts and announcements from officials. NYC Emergency Management will send emergency alerts and updates to New Yorkers through various channels.
Sign up for Notify NYC, the City of New York's official, free emergency communications program. Register for emergency notifications by getting the free Notify NYC mobile application, visiting NYC.gov/notifynyc, contacting 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115) or following @NotifyNYC on Twitter. (Notify NYC messages are available through many formats, including email, text messages, telephone, the Notify NYC website, RSS, Twitter, and American Sign Language videos.)
Keep a battery-operated AM/FM radio tuned to a local station and follow emergency instructions.
If it is safe to evacuate, leave and take your Go Bag with you.
If you are caught inside by rising waters, move to a higher floor. Take warm clothing, a flashlight, and portable radio with you. Wait for help. Do NOT try to swim to safety.
Do not use the telephone or any electrical appliance connected to the building's electrical wiring.
Do not use showers, sinks, or any object, machine, or device connected to the building's plumbing system. If lightning strikes the building, the current will likely flow through either the electrical wiring or the water pipes, and you could receive a fatal shock.
Exercise caution when traveling. Do not drive your vehicle or walk into areas where water covers the roadway as the water depth may be too great to allow you to cross safely. Use mass transit if possible.
If you are caught outside during a storm:
Avoid walking and driving through flooded areas. As few as six inches of moving water can knock a person over. Six inches of water will reach the bottom of most passenger cars, causing loss of control and possible stalling. One or two feet of water can carry away a vehicle.
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.
Stay out of any building if it is surrounded by floodwaters. Avoid flooded subway stations.
If you see downed electrical wires, do not go near them. Never attempt to move or touch them with any object. Be mindful that tree limbs, leaves, or water can cover downed wires from view. Always stay away from downed power lines because they could be live.
Strong winds can bring down trees and power lines and can turn unsecured objects into dangerous projectiles. They can also cause power outages. To prepare for these hazards, New Yorkers should:
Check the area immediately surrounding your home for unsecured objects or potentially dangerous conditions. Tree limbs, garbage cans, yard debris, or other materials that can be moved by the wind are potential projectiles aimed at your home or parked vehicle.
Bring inside loose, lightweight objects such as lawn furniture, potted plants, garbage cans, garden tools and toys.
Report downed wires immediately. If a power line falls on your car while you are in it, stay inside the vehicle and wait for emergency personnel.
If time permits:
Turn off all utilities at the main power switch and close the main gas valve if evacuation appears necessary. Do not touch any electrical equipment unless it is in a dry area, or you are standing on a piece of dry wood while wearing rubber-soled shoes or boots and rubber gloves.
Fill bathtubs, sinks, and jugs with clean water in case regular supplies are contaminated (you can sanitize these items by first rinsing with bleach).
Board up windows or protect them with storm shutters or tape (to prevent flying glass).
Bring outdoor objects, such as lawn furniture, garbage cans and other loose items, inside the house or tie them down securely.
To prepare for a possible power outage, charge cell phone batteries, gather supplies, and turn your refrigerator and freezer to a colder setting. If you lose power, items that need refrigeration will stay cooler for longer.
Make sure your flashlights and any battery-operated radios or televisions are working. Keep extra batteries.
If you lose power and have a disability, access and functional needs or use life-sustaining equipment and need immediate assistance, dial 911.
Do not use generators indoors.
Check on friends, relatives, and neighbors, especially older adults and people with disabilities, access and functional needs, or health conditions. Help them to prepare if needed.
What to Do After a Flood
Call 911 if you are in immediate danger.
Watch out for fallen power lines and stay away from damaged areas.
Tune in to local TV and radio for officials' announcements.
Before re-entering a building, check for structural damage. Make sure it is not in danger of collapsing. Turn off any outside gas lines at the meter or tank, and let the building air out for several minutes to remove foul odors or escaping gas.
Watch for electrical shorts or live wires before turning off the main power switch. Do not turn on any lights or appliances until an electrician has checked the system for short circuits.
Throw out fresh food and previously opened medicines that have come in contact with floodwaters.
New York City tap water is safe to drink, including in areas with flooding, unless otherwise reported by City officials. If your water service was disrupted, run the tap for at least 30 seconds and until the water runs cold and clear. Replace all ice machine filters and beverage dispenser filters, and flush all water lines for five minutes. Visit the NYC Department of Environmental Protection's website for any updates on New York City drinking water.
Assessing and Repairing Damage
Owners who want to reoccupy residences damaged by flooding should first hire a New York State-licensed Registered Architect or Professional Engineer to assess the building's safety. If the building is not safe to occupy, the owners should seek alternative housing arrangements while repairs are made. Owners should take pictures of all damage and flood impacts and keep receipts for all repairs if they intend to apply for disaster assistance or to make an insurance claim.
To make repairs, owners need to work with an engineer or architect who has the necessary City-authorized permits. The City advises residents to obtain two or three quotes from different contractors before beginning the work, which can vary widely in price depending on various field conditions. If an owner needs assistance with applications for permits, he or she should contact 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115).
Dry all areas and items quickly and thoroughly.
Dry clean 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.
The City works closely with the National Weather Service to monitor severe weather threats that could affect the five boroughs. The City uses several forms of outreach to alert the public in an emergency, including Notify NYC, the City of New York's official emergency communications program.
The City has several plans that focus on how to prepare for, respond to, and recover from flooding events. Before, during, and after a flooding event, the City monitors weather forecasts, and focuses on strategies such as catch basin cleaning and maintenance, and providing recovery assistance to affected households.