Extreme Heat

A photo of the sun at sunset.

Extreme heat is one of the most significant hazards facing New York City, and New Yorkers are especially vulnerable to extreme heat-related hazards during the summer months. Generally, extreme heat is defined by temperatures that hover 10 degrees or more above the average high temperature for the region, last for prolonged periods of time, and are accompanied by high humidity.

On warm summer days, the city can be as much as 10 degrees warmer than its surrounding areas. The city's infrastructure — largely made up of asphalt, concrete and metal — traps the heat. This is known as the "urban heat island" effect.

Know the Terms

  • Heat Index: an estimate of how it feels when air temperature and humidity are combined. See the National Weather Service Heat Index Chart for more information.
  • Heat Wave: the National Weather Service defines a heat wave as at least three consecutive days with high temperatures of at least 90°F.
  • Heat Advisory: in New York City, a Heat Advisory is issued when the heat index is forecast to reach 95°F to 99°F for at least two consecutive days or 100°F to 104°F for any length of time.
  • Excessive Heat Watch: issued by the National Weather Service when the heat index values are forecast to reach or exceed 105°F combined with nighttime low temperatures of 80°F or higher are forecast to occur for at least two consecutive days.
  • Excessive Heat Warning: issued by the National Weather Service within 12hours of an event when the heat index values are forecast to reach or exceed 105°F formore than 3 hours per day or two consecutive days, or the heat index is more than 115°F for any period of time.
  • Air Quality Index: reports how clear or polluted the air is. It is issued by the New York State Department of Environmental Conservation and relayed by the National Weather Service.

What to Do Before Extreme Heat

  • Protect your home from extreme heat.
    • Install high-performance windows and sunshades.
    • Check the condition of your air conditioning and ventilation systems.
    • Insulate your home.
  • Plan ahead to ensure your home and workplace are prepared for a potential loss of power. Have emergency supplies on hand in case of an outage. If you lose power, notify your utility provider immediately.

Know the Signs of Heat-Related Illnesses

Heat illness is serious. Prolonged exposure to the heat can be harmful and potentially fatal. Call 911 if you or someone you know shows signs or symptoms of heat illness, including headache, light headedness, muscle cramps, nausea, and vomiting. Learn more about heat-related illnesses and tips from the NYC Department of Health & Mental Hygiene.

What to Do During Extreme Heat

Stay Informed and Connected

  • 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.)
  • Check on your neighbors during a heat wave, especially if they are seniors, young children, and people with disabilities and access and functional needs.
    • Many older New Yorkers live alone and could suffer unnecessarily in the heat because they are isolated from friends and family.
  • Seniors and others who may be sensitive to extreme heat should contact friends, neighbors, or relatives at least twice a day during a heat wave.

Protect Your Health

  • If possible, stay out of the sun. When in the sun, wear sunscreen (at least SPF 15) and a hat to protect your face and head.
  • Use an air conditioner if you have one.
  • If you do not have an air conditioner, keep rooms well-ventilated with open windows and fans.
    • Consider going to a public pool, air-conditioned store, mall, movie theater, or cooling center.
    • Call 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115), or contact 311 online to find out whether a cooling center is open near you.
    • Note: these facilities are managed by agency partners who determine each site's hours of operation and level(s) of accessibility. For additional information, please contact these facilities directly.
    • Find a cooling center
    • Fans work best at night, when they can bring in cooler air from outside.
  • Wear lightweight, light-colored, loose clothing that covers as much of your skin as possible.
  • Drink fluids — particularly water — even if you do not feel thirsty.* (*People with heart, kidney or liver disease, or on fluid restricted diets should check with their doctors before increasing fluid intake.)
  • Never leave children, pets, or those who require special care in a parked car during periods of intense summer heat.
  • Avoid strenuous activity, especially during the sun's peak hours – 11 AM to 4 PM. If you must engage in strenuous activity, do it during the coolest part of the day, usually in the morning between 4 AM and 7 AM.
  • Cool showers or baths may be helpful, but avoid extreme temperature changes. Never take a shower immediately after becoming overheated – extreme temperature changes may make you ill, nauseated, or dizzy.
  • If you have asthma or other respiratory problems, stay in an area where it is cool and the air is filtered or air-conditioned.

For more information, visit NYC.gov/health.

Conserve Water

The improper opening of fire hydrants wastes 1,000 gallons of water per minute, causes flooding on city streets, and can lower water pressure to dangerous levels and hamper the ability of FDNY to fight fire safely and quickly.

Properly used "spray caps" reduce hydrant output to a safe 25 gallons per minute while still providing relief from the heat. To obtain a spray cap, an adult 18 years or older with proper identification can go to his or her local firehouse and request one.

Conserve Power

Power outages are most likely to happen during the hot summer months when utility usage is at its peak. During periods of intense electrical usage, such as on hot, humid days, it is important to conserve as much energy as possible.

Steps you can take to prevent an outage include:

  • Set your air conditioner thermostat no lower than 78 degrees.
  • Use the air conditioner when you are home. If you want to cool your home before you return, set a timer that turns on no earlier than 30 minutes before you arrive.
  • Turn off nonessential appliances.
  • Have emergency supplies on hand in case of an outage. If you lose power, notify your utility provider immediately.
  • If you lose power, notify your utility provider immediately.
  • Learn more about power outages

What the City Does

The City works closely with the National Weather Service to monitor extreme heat and related threats that could affect the five boroughs. The City uses several forms of media to alert the public in an emergency, including Notify NYC, the City of New York's official emergency communications program. The City also conveys information to service providers through the Advance Warning System.

During periods of extreme heat, when the heat index is predicted to be dangerously high, New York City opens cooling centers. Cooling centers are air-conditioned spaces such as senior centers, community centers, public libraries, and other public facilities that typically operate during daytime hours and are free and open to the public.

Additionally, the FDNY may distribute hydrant spray caps to conserve water. Opening hydrants without a cap results in a drop in local water pressure and threatens firefighting capabilities.

More Resources