Monsoon ‘slightly late’, may hit Kerala June 6, says IMD

NEW DELHI: Monsoon this year is expected to arrive over the Indian mainland five days later than the normal date and is likely to hit Kerala on June 6, the India Meteorological Department said on Wednesday. The normal date of monsoon’s onset is June 1.
The official weather agency’s forecast of a slight delay in the start of the rainy season comes a day after private weather forecaster Skymet released its onset prediction that said monsoon is likely to arrive on June 4, closer to the normal date.IMD’s forecast has an error margin of ± four days as opposed to Skymet’s margin of ± two days.
A delayed (or early) arrival has no impact on monsoon’s performance through the rainy season. In the past five years, monsoon was most delayed in 2016 but the season had normal rainfall at 97% of the long period average. The following year, monsoon arrived early (May 30) but rainfall was below normal (95%).

IMD said monsoon is likely to arrive over south Andaman Sea and Nicobar Islands around the normal date of May 18-19. Thereafter, the projected delay in reaching the Indian mainland is because the mid-latitudinal westerly system — the wind flows that bring rain-bearing western disturbances into north India through winter and spring — are still strong.
“The westerly system appears to be offsetting the establishment of the monsoon system. That’s the main reason why there’s likely to be a delay,” said P Sivananda Pai, IMD’s lead monsoon forcaster.
In 2006, IMD established a set of objective criteria for declaring the monsoon’s arrival over Kerala. These include rainfall, depth of westerly winds over a particular area over Arabian Sea and outgoing longwave radiation measured by satellite.
Under the rainfall criterion, 60% of 14 identified weather stations in Kerala should report rain of at least 2.5mm for two consecutive days for monsoon’s arrival to be declared. During the progress stage, a line known as the northern limit of monsoon separates the areas that have come under the monsoon system from others that are outside it.