This study investigates non-tropical cyclone (TC) related boreal winter heavy rainfall events that lead to extensive flooding (HRF) over the Philippines through a case study and composite analysis. The HRF event examined occurred during January 16–22, 2017 over Cagayan de Oro City (CDO) in Mindanao Island (122–127°E, 5–10°N). The accumulated rainfall over CDO reached by about 180 mm from 00 UTC January 16 to 00 UTC January 17, 2017, exceeding the climatological maximum daily rainfall in January over this area. The interaction of a westward propagating cyclonic circulation over Mindanao Island (MCC) and a shearline that is associated with an eastward-propagating cyclonic and anticyclonic circulations along 20–40°N, led to enhanced moisture convergence and rainfall over CDO. The climatology of these non-TC related HRF events was examined through composite analysis of the HRF events documented in the Dartmouth Flood Observatory archive from 1979 to 2017. The authors identified 34 of such cases over the Philippines, in which 25 occurred over Mindanao Island. The composites of the circulation features of these 25 cases resemble those during the January 2017 case. A vorticity budget analysis was performed to explain the propagation tendency of the MCC. The results show that the MCC only propagated westward when the magnitudes of the stretching and advection terms of the vorticity tendency equation are almost comparable with each other, together with the weakening of the southerly winds around Mindanao Island. This study reveals how cold fronts over the north Pacific together with the MCC induces HRF events over the Philippines.

这项研究通过案例研究和综合分析，调查了与热带气旋（TC）有关的北方冬季暴雨事件，这些事件导致了菲律宾的大面积洪水（HRF）。所检查的HRF事件发生在2017年1月16日至22日在棉兰老岛（122-127°E，5-10°N）的卡加延德奥罗城（CDO）上。从2017年1月16日世界标准时间到2017年1月17日世界标准时间，CDO上的累计降雨量达到了约180毫米，超过了该地区1月的气候最大日降雨量。棉兰老岛（MCC）上的向西传播的气旋环流和与20-40°N上的向东传播的气旋和反气旋环流相关的切变线的相互作用，导致CDO上的水分会聚和降雨增加。通过对达特茅斯洪水观测台存档于1979年至2017年的HRF事件进行综合分析，对这些与非TC相关的HRF事件的气候进行了分析。作者确定了菲律宾上空的34例此类事件，其中25例发生在棉兰老岛上。这25个案例的发行特征的综合与2017年1月的案例相似。进行了涡度预算分析以解释MCC的传播趋势。结果表明，MCC仅在涡旋趋势方程的伸展和平流项的大小几乎彼此可比，并且棉兰老岛周围的南风减弱时才向西传播。