This dataset provides water temperature measurements at the Luminao reef flat, Guam, in 2014 to 2015. They were conducted by the Raymundo Lab (University of Guam, Marine Laboratory), using an in situ mounted temperature logger that logged with an hourly resolution. They provide background temperature conditions at the native reef site of the Pocillopora acuta mother colonies' thermal acclimation study. Diurnal temperature characteristics are provided as daily minimum, maximum, and mean temperature values including the standard deviation around mean temperature.