The Sinharaja lies within a rainfall range of 3,000 to 6,000 millimeters. Rainfall figures available for the last 60 years show values ranging from 3,614 to 5,006 millimeters in places, in and around the Sinharaja .The mean monthly rainfall data for the year 1981 to 1984 given indicates the general pattern of rainfall with a minimum of 50 millimeters even during the driest month and two distinct monsoonal peaks.

The high annual temperature of the Sinharaja is typical of the tropics, recording little seasonal variation, but with marked daily ranges. The lowest mean monthly temperature has been abserved during the wettest season and the highest during the driest season. Conventional temperature patterns however change during long periods of drought or excessive rainfall. Some details of temperature and relative humidity recorded during the last 60 years.