The Southwest Monsoon has set in over Kerala, Nagaland, Manipur, Mizoram and Arunachal Pradesh on Tuesday, according to an official statement by the India Meteorological Department (IMD). It is expected to advance into parts of Karnataka and Tamil Nadu, and Goa within the next week.
“For the next 15 days, we see no factors that could impede the monsoon’s progress,” K.J. Ramesh, Director General, IMD, told The Hindu , “There will, however, be stronger rains across the western coast than the peninsular India.”
On May 16, the IMD said the monsoon would set in over Kerala two days earlier than its usual June 1 date.
While a timely arrival has no bearing on the spread and quantum of rainfall, meteorological agencies across the world, including India, largely concur that the threat of an El Nino has significantly decreased. This anomalous warming of certain portions of the equatorial Pacific is frequently responsible for drying up monsoon rains and, until last month, there was a 40% chance of an El Nino emerging during August.
The latest El Nino outlook, according to the IMD’s models, now puts it at about 18%. Century-old climate records suggest that the odds of an El Nino developing in any given year are 23%.
Mr. Ramesh explained that as due to an “inherent uncertainty [also called the spring barrier effect] ” in forecasting an El Nino between February and May. “ We had suggested as much in our April forecast…for now we maintain that monsoon will be near normal [or 96% of average of 89 cm]. A more detailed update [on how much rains are expected in key months such as July and August and the geographical distribution] will be available before June 10.”
The IMD declares the monsoon’s arrival over Kerala on the basis of an indigenously developed statistical model. These include minimum temperatures over Northwest India, ii) pre-monsoon rainfall peak over south Peninsula, iii) Outgoing Long wave Radiation (OLR) over south China Sea, (iv) Lower tropospheric zonal wind over southeast Indian ocean, (v) upper tropospheric zonal wind over the east equatorial Indian Ocean, and (vi) Outgoing Long wave Radiation (OLR) over the south-west Pacific region. Kerala had registered widespread rainfall over two days with 78% of monitoring stations reporting rainfall, a key factor that prompts the IMD to declare the monsoon’s arrival.
In 12 years, according to a statement, the monsoon has always arrived within a 4-day window of the IMD’s forecast. The Year 2015, when the monsoon arrived on June 5, instead of the predicted May 30, was the only exception.
The cyclonic storm Mora that landed in Bangladesh on Tuesday helped the monsoon reach the Northeastern states, according to Mr. Ramesh.
