IMD predicts normal monsoon

The India Meteorological Department (IMD) today forecast a normal monsoon across the country this year.

Lending a quantitative perspective to the available indications, IMD said the total rainfall during the June-September monsoon season would be 98 per cent of the long period average. This assessment is subject to a model error of ± 5 per cent.

But, there is yet no indication of when the monsoon would set in over the country. It normally hits the Kerala coast or the northeast region around June 1. It advances further to reach Mumbai and Kolkata by about June 10 and Delhi by June 29. By mid-July, the entire country ought to be covered by the monsoon.

The long-range forecast for the 2010 monsoon is based on a five-parameter statistical model and would be fine-tuned with the help of another six-parameter statistical model in June. Three parameters are common in both the models, IMD said in a statement today.

It would release the updated forecast by June, after the monsoon has set in.

It would simultaneously issue its predictions for the rainfall in four homogenous geographical regions of the country as also for the agriculturally crucial month of July.

Last year too IMD had predicted a near-normal rainfall of 96 per cent. Two months later, in June, it issued an update scaling down its assessment to 93 per cent of normal. Both these predictions went awry. IMD then revised its forecast for a third time in August, this time predicting 87 per cent of normal rains.

These predictions, however, turned out wrong and the country received only 77 per cent of normal rainfall. This led to a drought in large parts of the country.

Since 2007, IMD is using two new statistical monsoon models – one for preparing long range forecast to be issued in April and the other for its updated version in June. But these models are yet to establish their credibility as they have failed to accurately foresee the monsoon on two of the three years of their use.

Weather analysts, however, say IMD may be closer to the mark this year as most international weather organisations have also predicted normal monsoon for India in 2010.

Besides, IMD has taken into account the monsoon forecasts made by a large number of national and international weather organisations while preparing its own forecast. In addition, it has kept an eye on the state of El Nino (warming up of the Pacific ocean), which generally has a negative influence over the Indian monsoon.

“From late December, the El Nino conditions have started weakening. The latest forecasts from a majority of the dynamical and statistical models indicate high probability for the present El Nino conditions to maintain till early part of the monsoon season and then weaken to become near neutral during the subsequent months,” IMD said.

Some models indicate development of weak La Nina (opposite of El Nino, which is deemed favourable for the Indian monsoon) by July-August, 2010.

Since last year, IMD has also been generating the experimental monsoon predictions by using a dynamical forecasting system, similar to the ones used by most weather organisations in the developed countries. However, it does not make these forecasts public but uses them only as an input for computing its long range forecast.