Decatur weather in August 2026

Q: How hot is it in Decatur in August?

Daytime temperatures usually reach 28°C in Decatur in August with moderate heat and humidity, falling to 16°C at night.

Q: How sunny is it in Decatur in August?

There are normally 9 hours of bright sunshine each day in Decatur in August - that's 67% of daylight hours.

Q: How warm is the sea around Decatur in August?

The average sea temperature around Decatur in August is 21°C.

Q: Does it rain in Decatur in August?

There are usually 9 days with some rain in Decatur in August and the average monthly rainfall is 97mm.

Expect daytime maximum temperatures of 84°F in Decatur, Illinois in August based on long-term weather averages. There are 9 hours of sunshine per day on average with typically 3.7 inches of rainfall in the month.

84
84°F max day temperature
9
9 hours of sunshine per day
8
8 days with some rainfall
63
63°F min night temperature
14
14 hours of daylight per day
M
Moderate heat & humidity
3.7
3.7 inches of monthly rainfall
8
8 (Very High) UV index

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The August weather guide for Illinois (Decatur) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C) | Imperial (°F)