About the Southeast Heat Monitor

View the Tool ☀️ Background ☀️ About WBGT ☀️ Using This Tool ☀️ Hot Zones ☀️ Health Messaging ☀️ Data Details

Background

The Southeast Heat Monitor was developed as part of a multi-year project funded by NOAA’s Modeling, Analysis, Predictions, and Projections (MAPP) program. Together with collaborators at the North Carolina Institute for Climate Studies and Embry-Riddle Aeronautical University, this project provided the most comprehensive picture to date of heat vulnerability across the Southeast US.

The first phase of this work produced an historical analysis of heat stress, including trends in extreme heat and a regional climatology of the Wet Bulb Globe Temperature – one of the best indicators of heat and its impacts on people living, working, and playing outdoors.

That research is embedded and applied within the Southeast Heat Monitor tool, which shows forecasted heat stress with climatological context to highlight the days when heat stress is unusually high for a given time of year. This tool also includes health-focused messaging targeted toward specific at-risk groups based on the forecast and the season.

A photo of weather sensors used for assessing heat stress
Weather sensors measuring air temperature and black globe temperature inform our knowledge of past and present heat risk across the Southeast region. (Photo by the NC State Climate Office)

About WBGT

We’re used to measuring the temperature by the thermometer, and metrics like the Heat Index can indicate how hot it feels by factoring in both heat and humidity. However, the air temperature and Heat Index each miss an important factor that affects how we perceive the heat: because they’re measured in the shade, they don’t include the impact of direct sunlight.

That’s where the value of the Wet Bulb Globe Temperature (WBGT) emerges. First developed by the US military to inform their outdoor exercises, it captures the full range of conditions – including the temperature, humidity, winds, and exposure to sunlight – that affect how humans perceive the heat. In recent years, WBGT has been adopted by other groups including the North Carolina High School Athletic Association to inform outdoor exertion and break time.

WBGT can sometimes be confusing because its numerical scale differs from that of air temperature and Heat Index. Rather than focusing on these values, the Southeast Heat Monitor emphasizes the five color-coded threat levels, while also referencing the more familiar temperature and Heat Index metrics, to provide a more complete overview of forecasted heat risks and their potential health impacts.

For more information about WBGT and other heat metrics, please see our Extreme Heat Dashboard.

An infographic summarizing the WBGT calculation based on air temperature, natural wet bulb temperature, and black globe temperature
WBGT is calculated using a combination of air temperature, natural wet bulb temperature, and black globe temperature. (Graphic from the Nicholas Institute for Energy, Environment & Sustainability)

Using This Tool

The Southeast Heat Monitor is designed to show short-term heat risk forecasts over the next three days. When the tool first loads, a dropdown menu at the top allows for changing the selected date and displaying that forecast on the map. The layer control panel above the map can toggle between the default maximum Wet Bulb Globe Temperature forecast and the Hot Zones.

While using the tool, you may want to select a location in order to see the detailed local forecasts for that area. The tool will attempt to determine your location automatically using your browser or device. You can also select a custom location using the three buttons in the top right corner of the map. These will trigger a manual geolocation, prompt you to enter a city or address, or allow you to click on the map to set a custom location.

On the map, you can also toggle county lines and city/town names using the two buttons on the left. These reference layers may make it easier to assess local conditions. Finally, clicking on the map will display a popup showing the forecasted heat risk onset timing of each WBGT category at the selected location.

A screenshot of the Southeast Heat Monitor showing a map popup with heat risk timing at a selected location
Clicking the map will show a summary of heat risk onset timing for that location.

Beneath the map, you’ll find the legends for the layers being displayed. Once a location is selected, a panel will load beneath the legends showing the full three-day forecast details for that point. This includes the threat level and heat risk category for each date based on its maximum WBGT, a graph of the air temperature, Heat Index, and WBGT progression throughout the day, and a summary of heat health notes and recommended actions based on the forecast.

Across the tool, a number of options are available to share or export the forecast information:

  • In the title bar, the Link to this Location option will give a permalink to the selected location. By bookmarking this link, you can easily view your local forecast every time you come to the Heat Monitor.
  • In the layer selection panel, the Screenshot button will save an image of your current map view and its associated legends. These images can be used in publications, presentations, or easily shared with others.
  • In the daily forecasts panel, the Screenshot button will save an image of that local three-day forecast, including the daily progression graphs.
  • In the Heat Health Notes section, the Copy icon in the top right corner will copy that messaging as text to your clipboard, allowing you to easily paste, save, and share it with others.
A screenshot of the Southeast Heat Monitor showing an example of the Daily Forecasts panel for a particular location
Once a location is selected, the daily forecasts panel will load with the full three-day forecast and health messaging.

Hot Zones

How can you tell when a hot summer day crosses the line to become a hazardous heat event? That’s the purpose of the Hot Zones layers in the Southeast Heat Monitor. By comparing forecasted conditions against the full range of historical WBGTs on that same day of the year, we can tell how extreme or uncommon those conditions are.

This provides value all throughout the heat season. In the spring, when heat tolerance is lower after several cooler months, the Hot Zones can show when those first hot days of the season stand out. Over the summer, when hot weather is the norm in many areas, the Hot Zones highlight those unseasonably warm days that may see stress emerge sooner. And throughout the season, knowing the rarity of expected conditions can inform messaging to avoid overwarning and target specific groups likely to be affected by the heat.

Once you’ve selected a location in the Southeast Heat Monitor tool, the daily forecasts panel will automatically show the local forecasts, including any Hot Zones corresponding to each date. These Hot Zones range in rarity across five different levels:

  • Above Average: hotter than the historical mean value for this day of the year
  • Uncommon: hotter than the mean plus one standard deviation for this day of the year
  • Top 10%: above the 90th percentile, or within the hottest 10% of historical days on this day of the year
  • Top 5%: above the 95th percentile, or within the hottest 5% of historical days on this day of the year
  • Top 1%: above the 99th percentile, or within the hottest 1% of historical days on this day of the year

You can also toggle these same Hot Zones as overlays on the map interface. This will highlight the geographical areas within each of these climatological categories.

A screenshot of the Southeast Heat Monitor showing an example of the Top 1% Hot Zone layer
In this example, parts of eastern North Carolina are within the Top 1% Hot Zone layer.

Health Messaging

Because of its direct connections to how humans are affected by the heat, WBGT lends itself to health-related messaging. This language is baked into the Southeast Heat Monitor tool and appears in the daily forecasts for the selected location.

Specific language is included focused on:

  • Flag-based criteria and activity guidelines from the North Carolina High School Athletic Association
  • The WBGT category or threat level and corresponding heat onset and break time recommendations, as well as at-risk groups
  • The highest matching Hot Zone, or historical percentile for this time of year
  • The season and any common risks it carries with outdoor exposure

Each of these areas includes specific actions that can be taken to reduce the likelihood of heat illness and other health impacts. Thanks to the North Carolina Department of Health and Human Services for their assistance with reviewing this language using existing research and heat health guidelines.

A table of the WBGT-based WBGT activity guidelines used by the North Carolina High School Athletics Association
WBGT-based flag criteria and activity guidelines for athletes, which is part of the health messaging in the Southeast Heat Monitor.

Data Details

The daily forecasts shown in the Southeast Heat Monitor come from the National Weather Service’s National Digital Forecast Database. These represent the official local forecasts, provided at the native resolution of 2.5-kilometer (1.6-mile) grid cells. The forecast grids shown in the Southeast Heat Monitor are updated every night between April and October.

When viewing local forecasts for a specific date, note that the temperature, Heat Index, and WBGT data is available every hour for Day 1, then every three hours for Day 2 and Day 3. This is based on the temporal resolution of the original NDFD grids.

The historical percentiles were calculated from the ECMWF ERA5-Land reanalysis dataset, which covers the time period from 1950 to 2025. ERA5-Land was chosen because of this long period of record, as well as its inclusion of air temperature, relative humidity, wind speed, and solar radiation data – all key variables for calculating Wet Bulb Globe Temperature. In order to capture coastal areas not covered by the ERA5-Land product, these percentile grids blend in the standard ERA5 dataset over the water.