The onset and advance of southwest monsoon are accompanied by the appearance of the offshore trough along the southwest coast of India. This offshore trough escorts a deluge of rainfall to the southwest coast, and sometimes rainfall band moves eastward further into south India. These broad observations were noticed during the summer monsoon of June 2017. Meteorological agencies and media had reported a huge amount of rainfall over the southwest coast of India during the month. But, in the far interior of south India, rainfall was less. Due to the less rainfall, water resources depleted, which affected local farmers and common man of south India. The confused views of the common man on southwest coast rainfall could be due to lack of understanding related to various factors affecting rainfall over the same region. This article is an endeavor to address the preliminary understanding of the southwest coast rainfall during June 2017, with more stress on offshore troughs. The study begins with area-averaged rainfall statistics over south, southwest, and southeast India by employing satellite and rain gauge merged rainfall datasets. Area averaged analysis revealed offshore trough contributed 80 % of rainfall over the South West India, 68 % over South East India, contributing to an overall 75 % over south India in 2017. To identify offshore trough position and strength in the reanalysis and model simulations, a new method called VSV (Vertical Shear of Vorticity) method was introduced. The computed offshore troughs were categorized into Active, Normal, and Feeble based on the strength of meridional gradient of mean sea level pressure and 850 hPa horizontal winds. The contribution due to each category of the offshore trough over different sub-regions was investigated to find out the effect of the offshore trough to total rainfall. Dynamic and thermodynamic features of these categories of the offshore trough were investigated by using proxies like equivalent potential temperature and moisture flux convergence. We found that during active offshore trough an eastward propagation of rain bands persists, which was explained by using moisture flux convergence and equivalent potential temperature at different levels of the atmosphere.

西南季风的爆发和发展伴随着印度西南沿海近海槽的出现。这个近海槽护送大量降雨到西南海岸，有时降雨带向东移动到印度南部。这些广泛的观测结果在2017年6月的夏季风中被注意到。气象机构和媒体报道称，印度西南海岸本月降雨量很大。但是，在印度南部的偏远地区，降雨较少。由于降雨较少，水资源枯竭，这影响了印度南部南部的当地农民和普通百姓。普通人对西南海岸降雨的困惑观点可能是由于对影响同一地区降雨的各种因素缺乏了解。本文旨在解决对2017年6月西南海岸降雨的初步了解，并加大对海槽的压力。该研究首先通过采用卫星和雨量计合并的降雨数据集，对印度南部，西南和东南部地区的平均降雨量进行统计。面积平均分析显示，2017年西南印度洋降水占近海槽的80％，印度东南部占68％，2017年占印度南部总体的75％。要在重新分析和模型模拟中确定近海槽的位置和强度，介绍了一种称为VSV（垂直剪切）的新方法。根据平均海平面压力和850 hPa水平风的经向梯度强度，将计算出的海槽分为活动，正常和微弱。研究了不同分区上每种类型的近海槽的贡献，以找出近海槽对总降雨的影响。通过使用等效等效温度和水分通量收敛等代理研究了这些类别的海上槽的动力和热力特征。我们发现，在活跃的海上低谷期间，雨带向东持续传播，这可以通过使用湿气通量收敛和不同大气层水平下的等效潜在温度来解释。通过使用等效等效温度和水分通量收敛等代理研究了这些类别的海上槽的动力和热力特征。我们发现，在活跃的海上低谷期间，雨带向东持续传播，这可以通过使用湿气通量收敛和不同大气层水平下的等效潜在温度来解释。通过使用等效等效温度和水分通量收敛等代理研究了这些类别的海上槽的动力和热力特征。我们发现，在活跃的海上低谷期间，雨带向东持续传播，这可以通过使用湿气通量收敛和不同大气层水平下的等效潜在温度来解释。