A normal rainy season likely

September 04, 2016 02:10 am | Updated September 22, 2016 05:00 pm IST - CHENNAI:

The question on everyone's mind right now is how this year's monsoon will turn out.

While the India Meteorological Department is yet to announce the long-range forecast for the northeast monsoon, weather experts and bloggers note that the monsoon this year may be ‘normal’ considering data from the past decades.

Meteorologists note that it is difficult to predict accurate details about the mosoon at this point of time. Normally, IMD comes out with an outlook by September-end.

S.B.Thampi, Deputy Director General of meteorology, Chennai, said: “We have identified certain weather parameters and collected data about the southwest monsoon behaviour to extrapolate it with numerical models. The influence of global weather parameters such as El Nino and La Nina is also taken into account. The IMD Pune, comes out with a long range forecast for the entire region based on the performance of the monsoon during previous months.”

Forecast at this point may not be accurate as weather pattern is still evolving. “We need to wait for a few weeks for more clarity and reliable predictions,” he said. Accurate forecast for each area can be done only a few days before the monsoon.

The statistical forecast system, which is based on the study of weather data of previous decades, was a traditional symptomatic method of IMD until few decades ago. Y.E.A.RAJ, former Deputy Director General of meteorology, said it is hard to predict the monsoon because of its volatile behaviour and influence on a smaller region unlike the southwest monsoon.

But, the overall opinion is, considering the weather data for the past four decades, this NE monsoon may be normal for Chennai. Pointing out that there were many pairs of good rainfall years in the past, he said if a particular year has had excess rainfall during NE monsoon, the following year too has either normal or excess rainfall.

Chennai experienced a good monsoon continuously for five years between 1976 and 1980. Another closer example is that of 2005, when the city endured extensive flooding, and 2006. “Considering this, we may have normal rainfall. Another indicator is that if the southwest monsoon provides excess rainfall, the NE monsoon may be subdued.

Some international meteorological sites including that of the United Kingdom and International Research Institute for Climate and Society, Columbia, have predicted a 20-40 per cent probability for excess or deficient rainfall, and 40-60 per cent of normal rainfall during the monsoon,” Mr. Raj said.

Weather bloggers too note that the Chennai may have normal rainfall this monsoon. K. Srikanth, who blogs at Chennaiyil Oru Mazhaikalam , said that in the past century, there have been 24 years when the city received excess rainfall.

Of these, 17 were followed by years with either normal or excess rainfall.

A closer look at the eight El-Nino years similar to 2015 shows that nearly 50 per cent of them have had normal rainfall the following year, he said.

Pradeep John, who runs the popular blog Tamil Nadu Weatherman, added that this year’s monsoon may have many cyclones and the actual volume of rainfall will depend on their movement and landfall.

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