Northeast monsoon arrives early in Tamil Nadu

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Bracing for rain: The RMC has issued an orange alert for six districts, forecasting heavy to very heavy rainfall on Friday | Photo Credit: C. VENKATACHALAPATHY

The wait for Tamil Nadu’s major rainy season is over, with the Regional Meteorological Centre (RMC) in Chennai on Thursday declaring the onset of the Northeast monsoon, five days earlier than its normal date of arrival, and coinciding with the withdrawal of the Southwest monsoon.

The RMC has issued an orange alert for six districts, including the Nilgiris and Madurai, forecasting heavy to very heavy rainfall of up to 20 cm on Friday. Heavy rainfall may occur at isolated places in various coastal and interior districts. Wet weather will prevail till October 21, with heavy rainfall in some places.

RMC officials said the monsoon arrival was declared as it fulfilled various criteria, including the onset of northeasterly winds and fairly widespread rainfall across the State.

While the Southwest monsoon ended with a 20% rainfall deficit in Tamil Nadu, the Northeast monsoon is forecast to bring normal rainfall. The Delta and southern regions have a reason to be optimistic, with above-normal rainfall forecast for these areas. While the north coastal areas may receive normal rainfall, north interior areas could see below-normal rainfall.

V.R. Durai, head of the Regional Weather Forecasting Centre, RMC, said that while El Niño was expected to strengthen further this year, its impact on rainfall in Tamil Nadu would also depend on other climatic factors, including weather systems in the Bay of Bengal and cyclone tracks.

“The Bay of Bengal churns out fewer cyclones and low-pressure areas during El Niño years, even though it is associated with above-normal rainfall. Strong El Niño conditions would prevail till February, after which it may begin to lose strength,” he said.

On forecasts of extreme weather events, he said such events cannot be predicted a month ahead under the current circumstances, as atmospheric conditions changed with each passing day. While coastal areas could face severe weather events, weather tools cannot estimate the exact amount of extreme rainfall well in advance, he said.

A few coastal areas, including Karaikal, Puducherry, and Nagapattinam, fell within the zone of uncertainty in model predictions, he said.

Meanwhile, meteorologists said an early monsoon onset does not offer significant advantage in terms of seasonal rainfall. Y.E.A. Raj, former Deputy Director-General of Meteorology, said an early onset, seven or eight days ahead of schedule, does not guarantee good rainfall.

Citing weather data since 1901, he said that in the 12 years when the Northeast monsoon set in between October 1 and 10, Tamil Nadu received above-normal rainfall in only half of those years, including 1996 and 1977. However, in the six years when the monsoon set in late in November, including 2000 and 1992, Tamil Nadu ended the season with a rainfall deficit, he added.

Minister for Revenue and Disaster Management K.A.