Temperature increases and altered precipitation amounts and distribution may affect tree growth rates and seasonal dynamics. Tropical moist seasonal forests are distributed on limestones (karst) with shallow soil layers and poor soil water-retention capacity, making plant growth more vulnerable to seasonal drought. This study aims to investigate the seasonal dynamics of radial tree growth in a tropical moist seasonal forest and their response to environmental factors. Using a high resolution dendrometer, we monitored the radial stem growth of a deciduous tree species (Melia azedarach) in a tropical moist seasonal forest in Xishuangbanna, Yunnan for two consecutive years. We analyzed the seasonal dynamics of its radial growth and their associations with environmental factors. Our results showed considerable inter-annual differences in growth phenology (start, end, and duration) of Melia azedarach. Compared to a normal year (2018), the radial growth started and ended later in a drier year (2019), resulting in decreased annual growth. The decreased growth rate and shorter duration in 2019 may be due to the late onset of the rainy season and a severe and persistent heat wave during the early growing season. Daily growth of Melia azedarach correlated positively with daily rainfall and relative humidity, but negatively with photosynthetically active radiation, water vapor pressure deficit, and wind speed, indicating that the radial growth was mainly limited by water deficit. Moreover, the radial growth of Melia azedarach in the dry year (2019) showed a high correlation with precipitation and relative humidity. Our results provide clues for understanding climate sensitivity of tree growth in tropical moist seasonal forests and their adaptations to seasonal dry climates.