T. Ramakrishnan

It is expected to have normal intensity despite the delay

48 per cent of Tamil Nadu annual rainfall during the season

No correlation between delayed monsoon and failure

CHENNAI: The much-awaited northeast monsoon, the usual date of onset of which is October 20, is likely to break over Tamil Nadu in a day or two.

Deputy Director-General of Meteorology Y.E.A. Raj told The Hindu on Monday that going by the output of dynamical models, the onset was expected by Wednesday or Thursday. Despite the delayed onset, the monsoon is likely to be normal, as the El Nino phenomenon has been witnessed this year. “During El Nino years, the northeast monsoon has been, more often than not, normal or above normal,” Dr. Raj said.

El Nino refers to an anomalous rise in the Pacific Ocean sea-surface temperature off Peru’s coast along the equatorial belt. Usually this event, lasting nine months to a year, begins to form during June-August, reaches peak strength during December-April and subsides during May-July.

According to meteorological yardsticks, if the deviation from the average quantum of rainfall is minus 19 per cent to plus 19 per cent, it will make for a ‘normal’ monsoon.

The monsoon is important for Tamil Nadu: 48 per cent of the State’s annual rainfall of 945 mm is received during this season.

As for the delayed onset, the official noted that since 1979 the onset has occurred in the second half of October (16-31) on 16 occasions and in November four times (1984, 1988, 1992 and 2000). In the remaining 10 years it happened in the first half of October.

Dr. Raj said categorically that there was no correlation between delayed arrival and failure of the monsoon. In 1998, the onset happened on October 28. Yet, the State registered an excess of around 20 per cent.

As on date, Tamil Nadu had 78 per cent deficit in rainfall for the month of October. Against the normal 155 mm, it received 35 mm.

The senior official of the Meteorological Department said that going by the normal pattern of annual rainfall, the interior parts of the State reached the peak during October and the coastal parts in November. Some areas such as Nagapattinam and Vedaranyam got a good deal of rainfall even in December.