Weather system causes wet spell; to delay monsoon withdrawal

NT Bengaluru: A cyclonic circulation in central India is bringing rain to parts of India, including Karnataka, and delaying the withdrawal of the South West Monsoon (SWM). An India Meteorological Department (IMD) scientist made the disclosure to News Trail. Usually, SWM withdraws from the north western parts of the country, particularly Rajasthan around September 15. Moreover, SWM withdraws from Karnataka at the end of September or early October but not this time. This time, Rajasthan may see SWM withdrawal by September end instead. A cyclonic circulation is pulling moist winds and with it rain, towards the country. IMD scientist Puviarasan said the recent rains in Karnataka, including Bengaluru were the result of said weather system. “The monsoon withdrawal will be delayed,” Puviarasan said. “Normally, the withdrawal starts on September 15 in North West India but a (cyclonic) circulation is moving into central India. Due to that, parts of the country, including Karnataka, are getting rain,” he said, adding that a shear zone was also present. A shear zone is an area in the atmosphere where winds blow in nearly opposite directions, leading to atmospheric instability and potentially increased rain.

Little rain since mid-Aug: Puviarasan said although the perception was the quantum of rainfall was good this monsoon, the distribution between the months was uneven, adding that there had been little rain August 15 onwards. “After 15th August, there was not much rain in Karnataka. The Western Ghats and coastal Karnataka got some rainfall but the rest of the districts didn’t get rain,” he said. IMD revealed monsoon rainfall data for all 31 districts in Karnataka and only eight of them received deficit rainfall between June 1 and September 19. Kolar district received 207.8 mm of rainfall in said period. However, average rainfall for the district is 345.8 mm, making its 40 mm the highest deficit of any district. Other districts in deficit were Bidar, Dharwad, Kalaburagi, Dakshina Kannada, Hassan, Ramanagar and Bengaluru Urban. The latter district received 334.8 mm rather than its average of 383.9 mm. As many as 23 districts received excess rainfall. Chitradurga district received 419.4 mm of rain compared to its average of 243.6 mm, getting an excess of 72 mm of rain, the highest in the state. Puviarasan said the El Nino was neutral and the trend was moving towards La Nina but the same hadn’t set in.

3 conditions determine SWM end: As many as three conditions have to be met to declare the withdrawal of monsoon namely cessation of rainfall in the north west of the country, establishment of an anti-cyclone (clockwise winds in the northern hemisphere) in the atmosphere’s lowest layer and considerable reduction in moisture content as observed by satellite water vapour imageries.