Homeland Security and Emergency Services

sun

Heat - Terms to Know

  • Heat Wave: At least 3 days of abnormally high heat (90 degrees Fahrenheit or higher) and high uncomfortable humidity (80% relative humidity or higher) are expected.

  • Heat Index: A number in degrees Fahrenheit that tells how hot it really feels when relative humidity is added to the actual air temperature. Exposure to full sunshine can increase the heat index by 15 degrees. It also also known as the "Apparent Temperature"

  • Excessive Heat Watch: Heat watches are issued when conditions are favorable for an excessive heat event in the next 24 to 72 hours. A Watch is used when the risk of a heat wave has increased but its occurrence and timing is still uncertain.

  • Excessive Heat Warning: An Excessive Heat Warning is issued within 12 hours of the onset of extremely dangerous heat conditions. The general rule of thumb for this Warning is when the maximum heat index temperature is expected to be 105° or higher for at least 2 days and night time air temperatures will not drop below 75°.

  • Heat Advisory: A Heat Advisory is issued within 12 hours of the onset of extremely dangerous heat conditions. A heat advisory is issued when maximum daytime heat index values are forecast to reach 100 to 104°F for at least 2 consecutive hours.
        *Note: For New York City, a Heat Advisory is issued when the heat index is forecast to reach 95 to 99F for at least 2 consecutive days or 100 to 104F for any length of time.

  • Excessive Heat Outlooks are issued when the potential exists for an excessive heat event in the next 3-7 days. An Outlook provides information to those who need considerable lead-time to prepare for the event.

  • UV Index: A rough measure of the amount of harmful ultraviolet radiation in the sunlight reaching the Earth's surface at a given location, given the time of year and current atmospheric conditions, expressed in terms of the risks that are associated with exposure to that amount of radiation.