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NE monsoon deficient due to cyclones over Indian ocean
At least three out of four cyclones that formed over north of the Indian Ocean took moisture away from the main northeast monsoon region, affecting the northeast monsoon rains, said S Balachandran, Deputy Director General of Regional Meteorological Center. He was speaking at a seminar on monsoons, held in the city on Monday.
In 2018, the northeast monsoon recorded 24 per cent deficiency over TN and Rayalaseema, with Kerala being the only exception with normal rainfall, he observed. The observed pattern includes neutral El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) along with a favorable Madden Julian Oscillation (MJO) condition for a limited period.
MJO consists of two parts – enhanced and suppressed rainfall phases. Neutral ENSO period is when ocean temperature, tropical rainfall patterns and atmospheric winds over equatorial Pacific Ocean are near long-term average. Likewise, neutral IOD occurs when sea temperature changes a little across tropical Indian Ocean. Air rises above warm sea over northwest of Australia and sinks over western part of Indian Ocean with westerly winds along Equator. “Both background state as well as transient features were not favorable for a normal or excess northeast monsoon,” Balachandran explained the reasons for the failure of monsoon.
The southwest monsoon extended up to October 21 in 2018, thus delaying the onset of NEM to November 1. Between October and December, Manimutharu in Tirunelveli registered excess rainfall on November 3.
Cyclone Titli, classified as ‘very severe cyclonic storm’, made a landfall in October. It crossed Palasa, Srikakulam, and nearly 34 bulletins were issued. Likewise, the cyclone system Gaja originated from the low pressure area over the Gulf of Thailand and adjoining Malay Peninsula. It crossed TN and Puducherry coast between Nagapattinam and Vedaranyam with wind speed of 130 kmph gusting to 145 kmph, he recalled.
The event was aimed at analysing the performances of the southwest and northeast monsoons with radar features.