The La Nina phenomena, which gives a boost to Southwest Monsoon and was expected to give a good rainfall in September, has been delayed, the India Meteorological Department (IMD) today said, even as it stuck to its initial forecast of “above normal” rainfall this season.
IMD Director General K J Ramesh said as far as India is considered the “detrimental” El-Nino, which affected the Indian rains last year has reached a neutral stage.
“The El Nino which was detrimental to the Indian monsoon has faded and reached a neutral level. In the initial stages we were expecting La Nina to start, but it has been delayed now,” Ramesh told PTI.
He, however, refused to make any amends to the forecast.
Skymet, a private forecasting agency, has already downgraded its forecast from “above normal” rainfall to “normal”.
“We have made a forecast of 106 per cent of the Long Period Average with the model error of plus or minus four per cent. So, we are on the track,” Ramesh added.
In the IMD parlance, 96-104 per cent of the Long Period Average is considered as normal rainfall and anywhere between 104 to 110 is termed as above normal. Rainfall above 110 per cent of the LPA is considered as excess.
The La Nina was to start by August-September, but the cooling of ocean surface temperature is taking a longer time for the phenomenon to occur. As per the initial forecast, September was to receive excess rains due to this phenomenon.
Indian Ocean Dipole (IOD) has not influenced the Monsoon 2016 so far, as it has been negative since the beginning of the season. Now, the Madden Julian Oscillation (MJO), which was earlier travelling in the favourable zone, is no longer supportive for Monsoon rains.
A ‘positive IOD’ is associated with cooler than normal sea-surface temperatures in the eastern equatorial Indian Ocean and warmer than normal sea-surface temperatures in the western tropical Indian Ocean. The opposite phenomenon is called a ‘negative IOD’, and is characterised by warmer than normal SSTs.
El Nino is the unusual warming of sea-surface Pacific waters off the South American coast. La Niña is the positive phase of the El Niño and is associated with cooler than average sea surface temperatures.
The MJO, on the other hand, is a moving system of wind, cloud and pressure that brings rain as it circles around the equator.