The climate in Sematan is hot and humid. The average
annual temperature is 26.5 °C, with minimum and maximum
temperatures of 21 °C and 35 °C in September and
May, respectively; the mean annual relative humidity is
98% (data from the Malaysian Meteorological Service).
The annual rainfall in Sematan is 3563 mm (mean 1987–
1998) with January and May being the wettest and driest
months, respectively (data from the Sematan Fisheries
Station). Local tides have a semi-diurnal regime with a
maximum amplitude of 5.7 m (Sarawak Marine Department
1999).