''The southwesterly winds could strengthen further gradually from June 1, resulting in likely enhancement in rainfall activity over Kerala. Hence the monsoon onset over Kerala is likely to take place around June 3,'' the IMD said. Due to strengthening of lower level southwesterly winds, fairly widespread rainfall activity with isolated heavy falls are very likely over northeastern states during next five days. The normal onset date for monsoon over Kerala is June 1. This marks the start of the four-month rainfall season for the country. Earlier this month, the IMD had predicted the arrival of monsoon over Kerala by May 31 with an error margin of plus or minus five days. Monsoon is expected to be normal this year.