Diurnal Variation of Rainfall and Precipitable Water over Siberut Island off the Western Coast of Sumatra Island

Surface meteorological observations indicate that the diurnal cycle of rainfall over Siberut Island is characterized by dual maxima in the afternoon and after midnight, with the minima in the early morning and evening. The GPS-derived precipitable water (PW) over the island shows similar dual maxima in the afternoon and near midnight. The incident solar radiation during the morning hours is still sufficiently intense to generate local circulations on the island and to induce large diurnal variation of PW in the afternoon on days with daytime rain and days with nighttime rain. Meanwhile, a great increase of PW during the evening to nighttime is observed on days with nighttime rain. The results suggest a possibility that the increase of moisture during nighttime over Siberut Island, which is probably caused by the transport of water vapor from Sumatra Island, play a major role in formation of the nighttime rainfall over the island.