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Heat + high humidity = muggy! Understanding the ‘humidex’

It’s hot and humid in the upper North Island today. This muggy weather can be seen in our “Humidex” temperatures, also known as “feels like”.

The formulation to make the Humidex reading was given to us by Environment Canada (basically the Canada version of MetService).

The daytime highs we forecast simply measure the air temperature in the shade, but the Humidex is a subjective temperature based on adding humidity. Humidity makes a difference – a high of 25 degrees with low humidity is pleasant to be in, but 25 with high humidity can be stifling, exhausting and makes you extra sweaty.

The Humidex is a better way of measuring how hot it feels, and often upper North Island centres with highs in the mid 20s with high humidity can feel hotter than those with higher air temperatures (but drier air) further down the country.

When we have high humidity the air has more moisture in it… so when we as humans sweat, the sweat on our skin can’t evaporate as easily, so our skin gets wetter. Dry air does the opposite.

Muggy weather also leads to afternoon downpours and thunderstorms – as we’ve been seeing for the past two days.

You can see the CURRENT Humidex temperature in the “now” box in any of our WeatherWatch forecasts. As of 1:30pm many parts of the upper North Island had air temperatures in the mid to late 20s, but the Humidex reading says it feels more like 32 or 33C.

If you need FUTURE Humidex readings, we have hourly forecasts for all locations in NZ for 10 days out – simply jump over to

FYI – a cooler change is coming on Thursday with daytime highs down almost everywhere plus lower humidity levels in the north. You can see this in the graphs over at RuralWeather.


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