The heat index is a "feels like" temperature that combines air temperature and humidity to estimate how hot it feels in the shade. It is a useful public-comfort number, but it ignores sun and wind, so it under-warns for outdoor activity.
Last updated July 9, 2026 · Live data refreshes every 15 min
What it captures and skips
The heat index is a good answer to "how muggy will the walk feel?" It folds humidity into the temperature to reflect stalled sweat evaporation. What it deliberately leaves out is just as important: it has no wind term andassumes you are in the shade. On an exposed field, dock, or trail in the tropical sun, those omissions are exactly the factors that make heat dangerous.
Heat index vs. WBGT
For deciding whether it is safe to work or play outside, the heat index is the wrong tool and WBGT is the right one, because WBGT adds wind and radiant sun. The two numbers can disagree sharply on a bright, breezy USVI afternoon, read the full breakdown inWBGT vs. the heat index.
Frequently asked questions
Is the heat index measured in the shade or sun?
In the shade. The heat index assumes shade and light wind. Full sun can add the equivalent of up to 15°F that the heat index does not include, which is why it under-warns for outdoor activity.
Why does ClimaSafe use WBGT instead of the heat index?
Because the USVI is about outdoor decisions in the sun. WBGT adds wind and radiant heat, which the heat index ignores. See the full comparison of WBGT vs. the heat index.