Real-time heat-related illness

The weather forecast is the best way to predict heat-related health outcomes.

We can also track heat-related illness with near real-time electronic data from emergency departments at hospitals throughout NYC. These data include illnesses directly attributed to heat (including heat exhaustion, muscle cramps, fainting and heat stroke), not the full burden of heat-related health impacts.

We track these outcomes citywide by using a system called syndromic surveillance which lets us know how many people who visit the emergency room (ED) are being affected by certain health conditions. About 10,000 patients visit the ED per day in NYC, and reasons for their visits are captured in hospital records. These reasons are de-identified and sent to the Health Department. The Health Department then searches the records for diagnostic codes (when available) and words describing why patients are at the ED to track specific health conditions in near real-time and understand citywide trends.

Below are data on the number of heat syndrome visits to emergency departments, and the daily maximum temperature. What do we use these data for?


Extreme heat is dangerous. It can cause illness, make chronic conditions worse, and even kill. Heat-related illnesses - including heat exhaustion, muscle cramps, fainting, and heat stroke (the most serious form) - happen when the body cannot cool down enough. Heat can also worsen chronic conditions, such as cardiovascular diseases or kidney conditions.

In NYC, an extreme heat event is two or more days with a heat index reaching 95 °F, or one or more days reaching 100 °F.

To learn more about heat and health, visit Extreme Heat and Health. To stay safe in the heat, visit Beat the Heat.

Daily data: 2023

Data since 2017

Daily temperature: The maximum daily temperature is the heat index or temperature, whichever is higher, as recorded by the National Weather Service weather station at La Guardia Airport.