Extreme Heat

A photo of the sun at sunset.

Extreme heat is one of the most significant hazards facing New York City. 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.

During the summer months, New Yorkers are especially vulnerable to heat-related hazards. A heat wave's duration plays an important role in how people are affected. Heat waves are particularly dangerous for children, seniors, people with cardiovascular disease, and people taking psychotropic and other medications.

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.
  • Ultraviolet Radiation: ultraviolet or UV radiation, which is emitted by the sun, can damage the skin. UV radiation can lead to severe sunburn following an intense short-term overexposure, or serious skin cancers after long-term overexposure.
  • Heat Advisory: for New York City, a Heat Advisory is issued when the heat index is forecast to reach 95°F to 99°F for at least 2 consecutive days, or 100°F to 104°F for any length of time.
  • Excessive Heat: issued by the National Weather Service when the heat index values are forecast to reach or exceed 105°F for at least two consecutive hours.
  • Excessive Heat Watch: issued by the National Weather Service, 24 to 48 hours of an event when the heat index values are forecast to reach or exceed 105°F for at least two consecutive hours.
  • Excessive Heat Warning: issued by the National Weather Service within 24 hours of an event when the heat index values are forecast to reach or exceed 105°F for at least two consecutive hours.
  • UV Index: forecast of the amount of skin-damaging UV radiation expected to reach the earth's surface at the time when the sun is highest in the sky (solar noon). The UV Index can range from 0 (at night time) to 15 or 16 (in the tropics at high elevations under clear skies), with a higher numeric value corresponding to a shorter time required for skin damage to occur. See the National Weather Service UV Index Chart for more information.
  • Air Quality Index: issued by the New York State Department of Environmental Conservation and relayed by the National Weather Service when the Air Quality Index is forecast to exceed 100.
  • Heat Cramps are muscular pains and spasms, usually in the leg or stomach muscles, resulting from heavy exertion during extreme heat. Although heat cramps are the least severe of all heat-related health problems, they are often the first signal that the body is having trouble coping with the heat.
  • Heat Exhaustion occurs when body fluids are lost through heavy sweating due to vigorous exercise or working in a hot, humid place. Blood flow to the skin increases, causing blood flow to vital organs to decrease. Symptoms include: sweating, pale and clammy skin, fatigue, headache, dizziness, shallow breaths, and a weak pulse. If not treated, the victim's condition may escalate to heat stroke.
  • Heat Stroke is also called "sun stroke," and occurs when the victim's temperature control system, which produces perspiration to cool the body, stops working. The skin is flushed, hot and dry, and body temperature may be elevated. In fact, body temperature can rise so high that brain damage and death may result if the body is not cooled quickly. The victim may also be confused, develop seizures, breathe shallowly, and have a weak, rapid pulse.

Take Action

Stay Informed

  • When the heat index is predicted to be dangerously high, New York City opens cooling centers in air-conditioned public community centers, senior centers, and public libraries to offer people relief from the heat. 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.
  • Listen to local weather forecasts and announcements from officials. NYC Emergency Management will send emergency alerts and updates to New Yorkers through various channels.

Stay Cool: Cooling Centers

When the heat index is predicted to be dangerously high, New York City opens cooling centers in air-conditioned facilities, such as libraries, community centers, senior centers and NYCHA facilities, to offer people relief from the heat. Individuals who have no access to a cool environment, and particularly those at risk for heat-related illness, should use the cooling centers during a heat wave.

Call 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115) or contact 311 online during a heat emergency to find the location of a cooling center or pool, or use the online finder to choose a cooling center 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

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. Set the thermostat no lower than 78 degrees.
  • 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.
  • Fans work best at night, when they can bring in cooler air from outside.
  • Make a special effort to 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.
  • Drink fluids – particularly water – even if you do not feel thirsty.* Avoid beverages containing alcohol, caffeine, or high amounts of sugar.
  • Wear lightweight, light-colored, loose clothing that covers as much of your skin as possible.
  • 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.
  • During heat emergencies, the City may open cooling centers. If cooling centers are open, call 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115), contact 311 online, or locate a center online.
  • Know the signs of serious heat illness. Call 911 or go to the emergency room right away if you or someone you know has these symptoms of heat illness:
    • Hot, dry skin OR cold, clammy skin
    • Confusion, hallucinations, disorientation
    • Unconscious or unresponsive
    • Nausea or vomiting
    • Trouble breathing
    • Rapid, strong pulse
    • Weakness
    • Dizziness
  • Don't ignore the following warning signs of heat illness. If you or someone you know has warning signs of heat illness, get to a cool place, remove extra clothes, and drink lots of water:
    • Heavy sweating
    • Muscle cramps
    • Light headedness, feeling faint
    • Headache
    • Decreased energy
    • Loss of appetite, nausea
  • Hot summer weather can increase ozone levels and can negatively affect your health.
    • Know the signs of high ozone levels:
      • Chest pain
      • Coughing and wheezing
      • Lung and nasal congestion
      • Labored breathing
      • Nausea
      • Eye and nose irritation
      • Faster breathing
      • Sore throat
    • When ozone levels in the unhealthy range are expected, limit vigorous outdoor physical activity during the afternoon and early evening hours when ozone levels are at their highest.
    • If you have asthma or other respiratory problems, stay in an area where it is cool and the air is filtered or air-conditioned.
    • Outdoor exercise should be scheduled for the morning hours whenever possible.
*People with heart, kidney or liver disease, or on fluid restricted diets should check with their doctors before increasing fluid intake.

Conserve Water

  • Repair leaky faucets; turn taps off tightly.
  • Take short showers; only fill bathtubs halfway when taking a bath.
  • Run dishwasher and washing machines only when they are full.
  • Do not let water run while washing dishes, shaving or brushing your teeth.
  • Observe restrictions on watering your lawn or plants.
  • While it may be tempting to cool yourself off by opening a fire hydrant, open hydrants can lower local water pressure, hinder the efforts of firefighters, and endanger the lives of children who may be propelled into traffic by the force of the water. An open hydrant wastes 1,000 gallons of water per minute, overtaxes the sewer system and causes flooding of City streets.
    • If you observe a running fire hydrant, please notify the City by calling 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115), or contacting 311 online with its location.
    • If you experience low or no water pressure, notify the City by calling 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115), or contacting 311 online.
  • "Spray caps," which can be obtained from your local fire station, can be installed on any fire hydrant to produce a circular spray of cool water, reducing output to a safe level while still providing relief from the heat.
    • To obtain a spray cap, visit your local firehouse. You must be 18 or older to obtain a spray cap.

Conserve Power

While power outages occur infrequently in New York City, they 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 to avoid brownouts and other electrical disruptions. While diminishing your power usage may seem like an inconvenience, your cooperation will help to ensure that utilities can continue to provide uninterrupted electrical service.
  • Plan ahead to ensure your home and workplace are prepared for a potential outage. Have emergency supplies on hand in case of an outage. If you lose power, notify your utility provider immediately.
  • Take steps to remain cool. If this is impossible in the absence of electricity, go to a cool location such as a friend or relative's home, theater, restaurant, library or other air-conditioned facility, or 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.
  • Set your air conditioner thermostat no lower than 78 degrees — a 75-degree setting uses 18 percent more electricity and a 72-degree setting uses 39 percent more electricity. This setting allows for sufficient cooling while still conserving electric power.
  • Only use an air conditioner when you are home. If you want to cool your room down before you arrive home, set a timer to have it switch on no more than one-half hour before you arrive
  • Turn off all nonessential appliances.
  • Turn off lights in unoccupied rooms.
  • Only use appliances that have heavy electrical loads (dishwashers, washers, dryers) early in the morning or very late at night.

Help Reduce Ozone Levels

  • Avoid driving, especially on hot summer days. Use mass transit, walk, or carpool instead.
  • Be careful not to spill gasoline and fill your gas tank during the cooler evening hours.
  • Keep your car properly tuned and maintained.
  • Seal containers of household cleaners, solvents, and chemicals to prevent evaporation of chemicals that can contribute to ozone formation.

Learn more about power outages

Brush Fire Safety

New York City's outer-borough grasslands are prone to brush fires in the hot summer months, when vegetation is dry. Review safety tips for protecting your home and surroundings from brush fires.

More Resources

Heat-related illnesses and tips (NYC Department of Health & Mental Hygiene)