temperature at the end of august

I've been looking at weather forecasts for Calvi for the end of August and see normal daytime temperatures to be 25 to 27 degrees. Normal dry lapse times are about 1 degree per 100m. Does this mean normal temperatures at 1600m are going to be about 9 to 11 degrees? and nightime temperatures 0 to +3 degrees? If so, I think I need a better sleeping bag?