A network of 411 ground stations across Luzon Island, Philippines (12.5–20° N, 119–126.5° E) was used to characterize the diurnal cycles of summer precipitation, in terms of amount (PA), frequency (PF), and intensity (PI), during the southwest monsoon season (SWM; May–September) between 2011 and 2018. In addition to monsoon exposure, the effect of topography on the diurnal cycle of precipitation also was investigated by comparing a valley, plain, west- and east-facing coasts near mountains. Results show that monsoon exposure significantly influenced diurnal precipitation such that PA and PF decreased (PI increased) toward the leeward side of Luzon Island. Most topographies showed late afternoon-early evening peaks; however, the east-facing coast exhibited a late night-early morning peak. Orographic effects led to as high PA over mountains and enhanced the spatiotemporal propagation of PA in monsoon-exposed areas. The first (second) half of the diurnal peak exhibited high PI/low PF (low PI/high PF), suggesting both PI and PF are important indicators of PA. Finally, graded analysis revealed that light precipitation (0.01–2.5 mm h⁻¹) captured overall precipitation trends across Luzon Island, highlighting the importance of this intensity of precipitation. Heavy precipitation (2.5–7.5 mm h⁻¹) peaked in the morning; however, underlying mechanisms remain unknown. The study presents the first examination of the diurnal precipitation cycle in Luzon Island using a dense network of synoptic stations. The study demonstrates the complex effect of topography on precipitation and the importance of the SWM in the diurnal cycle of precipitation.

横跨菲律宾吕宋岛（北纬12.5-20°，东经119-126.5°）的411个地面站组成的网络用于表征夏季降水的日周期，其数量（PA），频率（PF）和强度（PI），在2011年至2018年之间的西南季风季节（SWM； 5月至9月）。除季风暴露外，还通过比较山谷，平原，西边和西边，研究了地形对降水昼夜周期的影响靠近山脉的朝东海岸。结果表明，季风暴露对昼夜降水有显着影响，使得朝向吕宋岛的背风侧的PA和PF降低（PI升高）。大多数地形显示下午晚些时候至傍晚高峰。但是，朝东的海岸却出现了深夜至清晨的高峰。地形效应导致山上PA的升高，并增强了季风暴露地区PA的时空传播。日峰值的前一半（后半部分）显示出高PI /低PF（低PI /高PF），表明PI和PF都是PA的重要指标。最后，分级分析显示，轻度降水（0.01–2.5 mm h^-1）捕获了整个吕宋岛的总体降水趋势，突出了这种降水强度的重要性。早晨达到最大降水量（2.5–7.5 mm h ^-1）。但是，基本机制仍然未知。该研究利用密集的天气观测站网络对吕宋岛的日降水周期进行了首次检查。该研究证明了地形对降水的复杂影响以及SWM在降水的昼夜循环中的重要性。