NEW DELHI: A western disturbance and formation of two lower pressure systems — one over Arabian Sea and the other over the Bay of Bengal — will continue to cause rainfall in different parts of the country till October 21, the India Meteorological Department said in its latest weather updates on Sunday. “There were two low pressure systems, one over the Bay of Bengal and another over Arabian Sea. There was some kind of interaction between these two low pressure systems,” said M Mohapatra, IMD director general, while referring to the reasons behind the current spell of rainfall. These interactions and heavy wind have primarily led to torrential rainfall in Kerala in the past 48 hours. It is now expected that these systems, mainly easterlies, may trigger onset of the northeast (winter) monsoon over the south Peninsula around October 26. The IMD, in its updates, said a western disturbance lying over Afghanistan and its neighbourhood was interacting with easterlies at lower levels from the Bay of Bengal. It is very likely to continue for the next two or three days and fairly widespread to widespread ‘light to moderate rainfall’ with heavy to very heavy rainfall at isolated places is very likely over different parts of northwest India, including Delhi-NCR, till Tuesday under its influence. “A fresh spell of easterly wave is likely to affect south Peninsular India from October 20 and cause fairly widespread rainfall with isolated heavy falls likely over Kerala and Mahe, south interior Karnataka and Tamil Nadu, Puducherry and Karaikal,” the IMD said, while noting that the situation may continue for subsequent 3-4 days. Though intense spell of rainfall activity over south peninsular India (Kerala and Mahe, South Interior Karnataka and Tamilnadu, Puducherry and Karaikal) is likely to reduce, heavy rainfall activity is expected over east and northeast India during October 18-21.