The measured value is "consistent with the trend in global average surface temperatures that has been observed during the past few decades," NASA said.
Last month was 0.85 degrees Celsius warmer than the mean August temperature from 1951-1980.
It was surpassed by August 2016, which was still affected by the 2015-2016 El Nino and was 0.99 degrees Celsius warmer than normal, according to the US space agency.
However, August this year was about 0.2 degrees warmer than the August following the last large El Nino event in 1997-1998.
The monthly analysis by NASA's Goddard Institute for Space Studies (GISS) in the US is assembled from publicly available data acquired by about 6,300 meteorological stations around the world, ship- and buoy-based instruments measuring sea surface temperature, and Antarctic research stations.
The modern global temperature record begins around 1880 because previous observations did not cover enough of the planet.
"Monthly analyses are sometimes updated when additional data becomes available, and the results are subject to change," NASA said.
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