The South-West monsoon this year is likely to be normal, according to India Meteorological Department (IMD).
In its long-range forecast bulletin issued on Friday, the IMD said that, quantitatively, rainfall during the June to September season would be 98 per cent of the long period average with a model error of plus or minus five per cent.
The long period average rainfall for the period 1941-1990 is 89 cm.
JUNE FORECAST
The IMD will update the forecast in June as a part of the second stage forecast. Separate forecasts for the monthly (July and August) rainfall over the country as a whole and seasonal (June-September) rainfall over the four geographical regions of India will also be issued.
The basic premise for the normal monsoon outlook seems to be the sustained weakening of El Nino conditions in the equatorial east and central Pacific.
During an El Nino, the equatorial Pacific waters to the east close to the South American shores warm up, causing cloudiness and precipitation to concentrate in that part of the world.
This brings sinking air motion and dryness to the west, affecting monsoon flows into India as well. A strong El Nino was in view during last year, causing the monsoon to end up with a 23 per cent deficit, the worst in three decades.
WEAK EL NINO
El Nino that remained weak during mid-June to October of 2009 started strengthening from late October and peaked in the third week of December, the IMD said.
From late December, the El Nino conditions have started weakening. Latest forecasts from a majority of weather indicate high probability for these conditions to maintain till early part of the monsoon season and then weaken to become near neutral during the subsequent months.
But a few models indicate development of weak La Nina conditions by July-August. As the lead time of the forecast increases there is considerable spread and uncertainty in these forecasts, the IMD said.
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