We investigate the characteristics and causes of extreme rainfall event occurred in Kerala (south western regions of the peninsular India) in August 2018. The changes in large-scale circulations over the Indo-Pacific domain and their association with regional circulation features, which made the extreme rainfall in Kerala are analysed. During this extreme event, Kerala experienced eleven days of incessant rainfall from 8 to 18 August 2018. It is observed that these extreme rainfall days were accompanied with two extreme spells of rainfall during 8–10 and 14–17 August 2018 that made severe floods in Kerala. Kerala experienced rainfall of more than 100 mm day⁻¹, particularly in the south Kerala during these events. The triad (average of three days) analysis of vertical velocity at 500 hPa and moisture convergence at the surface level reveal the dynamics and thermal structure of the regional deep convective activity. A remarkable eastward shift of cross equatorial flow over the Indian Ocean produced an intense offshore vortex, which induced more moisture towards the southern regions especially over Kerala where the extreme event was occurred. The west Pacific subtropical high (WPSH) is one of the large-scale circulations over the Indo-Pacific region, which shifted northward and the western flank of WPSH extended westward resulting a blocking high that was created over East Asia during the period. The eastward shift of cross-equatorial flow over the Bay of Bengal, outflow from the East Asian blocking high were mainly maintaining the low-pressure system over the Bay of Bengal during the extreme event. Therefore, the key cause of the extreme flood over Kerala in August 2018 is the deep moisture convergence through the offshore vortex, intense intrusion from subtropics and out flow from low-pressure system over the Bay of Bengal.

我们调查了 2018 年 8 月喀拉拉邦（印度半岛西南地区）极端降雨事件的特征和成因。分析了喀拉拉邦的极端降雨。在这次极端事件中，喀拉拉邦在 2018 年 8 月 8 日至 18 日期间经历了 11 天的持续降雨。据观察，这些极端降雨日伴随着 2018 年 8 月 8 日至 10 日和 14 日至 17 日期间的两次极端降雨，造成了严重的洪水。喀拉拉邦。喀拉拉邦每天降雨量超过 100 毫米^-1，特别是在这些事件期间在南喀拉拉邦。对 500 hPa 垂直速度和表层水分辐合的三元组（三天平均）分析揭示了区域深层对流活动的动力学和热结构。印度洋横赤道气流显着向东移动，产生了强烈的离岸涡旋，导致向南部地区尤其是发生极端事件的喀拉拉邦地区增加了更多水分。西太平洋副热带高压（WPSH）是印太地区上空的大规模环流之一，该环流向北移动，副热带高压西翼向西延伸，形成了这一时期在东亚上空形成的阻塞高压。孟加拉湾横赤道气流东移，东亚阻塞高压的流出主要是在极端事件期间维持孟加拉湾上空的低压系统。因此，2018年8月喀拉拉邦上空特大洪水的主要原因是通过近海涡旋深层水汽汇聚、亚热带强烈入侵和孟加拉湾低压系统外流。