The northeast monsoon is here. The Regional Meteorological Centre announced that NE monsoon has set in over Tamil Nadu and Puducherry on Saturday.
IMD has declared the arrival of NE monsoon over the region with various atmospheric conditions as criteria. The factors include strong northeasterly winds over parts of the Bay of Bengal, the well-marked low-pressure area over the southeast Bay of Bengal and another cyclonic circulation over the Comorin area.
Initially, rainfall activity may be subdued. The State may largely experience light to moderate rains for five days. Though a pair of weather disturbances on either side of south peninsular India have been steadily gaining strength, they would not trigger heavy rain spell over the State immediately.
While cyclonic storm Tej in the Arabian Sea is likely to intensify into a very severe storm by Sunday and move towards the Yemen-Oman coasts and make landfall by October 25, the weather disturbance in the Bay of Bengal would strengthen as a depression by Sunday and move towards Bangladesh and West Bengal coasts.
S. Balachandran, Additional Director General of Meteorology, Chennai, said there are chances for the system in the Bay of Bengal to move in a northwest or northerly direction, further away from the Tamil Nadu region. The changes in moisture distribution and the position of weather disturbance have dragged the rainfall activity away from this region.
The monsoon would pick up pace only after the two systems move and dissipate. Most parts of the State would receive light to moderate rains for four or five days. Heavy rains may be concentrated over parts of Kanniyakumari and Tirunelveli districts on Sunday. Chennai may have light/moderate rains in some areas till Monday.
Citing examples of 16 years when global weather parameters of El Nino and positive Indian Ocean Dipole prevailed during NE monsoon, Mr. Balachandran said Tamil Nadu had experienced normal or excess monsoon in most years. There are more chances of near normal monsoon rainfall this year.
Weather experts, however, noted that October is likely to end with deficit rain in Tamil Nadu. Y.E.A. Raj, former Deputy Director General of Meteorology, Chennai, said weather systems in the Arabian Sea would not impact NE monsoon flow. However, the Bay system would have to move westwards to hit Tamil Nadu and bring rains.
Citing long-range forecasts based on the south Indian Ocean convergence zone model by former IMD meteorologists, including Onkari Prasad, he said the model has predicted subdued rainfall activity this month. Tamil Nadu may experience 24% deficit in rainfall in October. Similarly, Chennai may face rain deficit of 43% this month.
