Tectona grandis (teak) is widely planted as high-quality timber in the seasonal tropics, yet detailed data on its seasonal water use and the effect of climatic fluctuations on its transpiration behaviour are limited. We measured sap flux density (SFD) using Granier's sap flow sensors for three wet and two dry seasons in the years 2012, 2014, and 2015 (wet season only) in 7 to 14 trees and made a calibration of Granier's equation for teak to calculate SFD for estimating whole-tree water consumption and stand-level transpiration. We also characterized the effects of daily rainfall, vapour pressure deficit, and photosynthetically active radiation on the daily SFD of individual trees. We found a large fluctuation in rainfall in the wet seasons of 2012 to 2015 (1,159 mm in 2012, 778 mm in 2014, and 727 mm in 2015). Total wet and dry season stand-level transpiration were 824 and 501 mm in 2012 and 446 and 214 mm in 2014, respectively, whereas the wet season transpiration of 2015 was 358 mm. Namely, reduced wet season rainfall reduced the total stand-level transpiration of teak at the study site. Most variations in daily SFD were due to differences in meteorological conditions, that is, day-time mean vapour pressure deficit, photosynthetically active radiation, and daily rainfall associated with the seasons of particular year. We also established models to estimate the stand-level transpiration of a teak plantation. The findings of the present study could be useful for forestation program and hydrological management in tropical regions with seasonal drought.