This study investigates the synoptic conditions that led to the heavy rainfall/flood (HRF) event in Mindanao Island, Philippines (122 −127°E; 5 −10°N), on January 2009 (JAN2009 HRF) that are less emphasized in previous works. Extensive flooding was reported over Cagayan de Oro City in the northern part of Mindanao, where the rainfall on January 10, 11, and 13, 2009, exceeded the 99th percentile of daily rainfall records of all January of the city from 1979 to 2017 by almost two times. A similar exceedance was also felt in Hinatuan station over the eastern coast of Mindanao Island on January 15, 2009. The interaction of a cold surge shearline over the northern Mindanao Island and the warm tropical easterlies led to enhanced moisture convergence. The warmer air mass is forced to ascend by the advancing colder air mass because it has lower density than the colder air mass. The enhanced moisture convergence and buoyancy difference by the air masses led to enhanced ascent and consequently rainfall along the cold surge shearline. Further analysis shows that enhanced anomalous easterly and northerly winds at 925 hPa are apparent over the Philippines. The anomalous easterly winds sustained the supply of warmer easterlies and collaboratively interacted with the northerly winds that supplied colder temperature air mass.

The climatology of this HRF event was examined for all January from 1979 to 2017. The authors identified 15 other cases that are similar to the JAN2009 HRF event and performed lag composite analyses. The results show that the occurrence of these HRF events is facilitated by the southward expansion of the high-pressure system to the north of the Philippines, enhanced cold and warm temperature advections, and enhanced moisture convergence along the cold surge shearline. The results of this study have important implications for disaster mitigation during the northeast monsoon season when rainfall activities are, in general, less intensive over this region.

本研究调查了导致 2009 年 1 月菲律宾棉兰老岛（122 -127°E；5 -10°N）发生强降雨/洪水 (HRF) 事件的天气条件 (JAN2009 HRF)作品。据报道，棉兰老岛北部的卡加延德奥罗市发生大面积洪水，2009 年 1 月 10 日、11 日和 13 日的降雨量几乎超过了该市 1979 年至 2017 年整个 1 月日降雨量记录的第 99 个百分位。两次。2009 年 1 月 15 日，棉兰老岛东海岸的 Hinatuan 站也感受到了类似的超标。棉兰老岛北部的冷潮切变线与温暖的热带东风的相互作用导致水分辐合增强。较暖气团的密度低于较冷气团，因此会被冷气团的推进迫使其上升。气团增强的水分汇聚和浮力差异导致沿冷潮切变线的上升和降雨增强。进一步分析表明，菲律宾上空明显增强了 925 hPa 的异常东风和北风。异常的东风维持了较暖东风的供应，并与提供较冷温度气团的北风相互作用。进一步分析表明，菲律宾上空明显增强了 925 hPa 的异常东风和北风。异常的东风维持了较暖东风的供应，并与提供较冷温度气团的北风相互作用。进一步分析表明，菲律宾上空明显增强了 925 hPa 的异常东风和北风。异常的东风维持了较暖东风的供应，并与提供较冷温度气团的北风相互作用。

从 1979 年到 2017 年的整个 1 月，对该 HRF 事件的气候学进行了检查。作者确定了 15 个与 2009 年 1 月 HRF 事件类似的其他案例，并进行了滞后综合分析。结果表明，这些 HRF 事件的发生是由高压系统向南扩展到菲律宾北部、冷暖温度对流增强以及沿冷涌切变线的水分辐合增强等因素促成的。这项研究的结果对东北季风季节的减灾具有重要意义，因为该地区的降雨活动通常不那么密集。