The much-hyped la Nina phenomenon, which was expected to give a boost to Southwest Monsoon especially in September, has been delayed.
According to the India Meteorological Department (IMD), it was to set in by August-September. But the cooling of ocean surface temperature is taking longer for the phenomenon to commence.
As per the initial forecast, September was to receive excess rains due to this trend. However, in the present situation, sources in IMD maintained that rainfall is likely to remain in the normal range. The weather models are being assessed on the basis of which a revised forecast would soon be released. As per IMD standards, average or normal rainfall ranges from 96 per cent to 104 per cent of a 50-year average of 89 cm for the entire four-month season.
According to weather experts, la Nina is unlikely to develop during monsoon season and even if it develops in October, it will be weak. It is associated with cooler than average sea surface temperatures and is the counter of El Nino which is the unusual warming of sea-surface Pacific waters off the South American coast. As per weather experts, rain deterrent El Nino has however already neutralised.
To add to the above, even the Indian Ocean Dipole (IOD) has not influenced the Monsoon this year, so far. As per the scientists, it has been negative since the beginning of the season. 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 sea surface temperatures.
To compound the woes further, the Madden Julian Oscillation, which was earlier travelling in the favourable zone, is no longer supporting for Monsoon rains either. This is a moving system of wind, cloud and pressure that brings rain in the region, as it circles around the equator.