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La Nina past its peak, says Australian Met Bureau

Vinson Kurian Thiruvananthapuram | Updated on February 25, 2021

IRI sees above normal early monsoon phase for India

The Australian Bureau of Meteorology (BoM) has said that the La Nina over the Tropical Pacific is still active but may have has passed its peak strength in February. The Bureau cited model forecasts from across the globe to suggest that the Pacific may return to ‘neutral’ (neither El Nino nor La Nina) conditions during March to May.

International Research Institute (IRI) for Climate and Society, Columbia University, agreed saying that in mid-February, sea-surface temperatures (SSTs) in the East-Central Pacific are roughly 1.1 degree Celsius below average, and most key atmospheric variables are consistent with continued La Nina conditions.

Likely dissipating in March-May

A large majority of the model forecasts predict SSTs to be cooler than the threshold of La Nina SST conditions through the Northern Hemisphere winter (December-February), dissipating during spring (March-May). There is an 82 per-cent chance of La Nina for the February-March-April season, and a likely transition in April-May-June. For the time being, a La Nina advisory remains in effect.

El Nino and alter ego La Nina events (seesawing of temperatures in the West and East of Pacific) tend to develop during April to June and reach their maximum strength during October to February. They typically persist for 9-12 months, though occasionally lasting for up to two years. Typically, they recur every two to seven years.

‘Neutral’ is ‘mixed’ for India

The Australian Bureau said that a La Nina typically increases the likelihood of above average rainfall across eastern parts of Australia during early autumn (March to May) while it is thought to have influenced the success of the Indian monsoon in 2020. ‘Neutral’ Pacific has traditionally brought mixed fortunes for India, which is poised to enter the pre-monsoon season as early as next week.

March-May outlook

The IRI’s February outlook for March-April-May suggests below normal rain for the central parts of India (Madhya Pradesh, Central Maharashtra, Telangana and North Interior Karnataka); above normal rain along the West Coast including Mumbai and neighbourhood, the East Coast as well as the rest of the South Peninsula (Tamil Nadu, South Interior Karnataka and Kerala).

East and North-East India and the adjoining Gangetic plains (Bihar, Uttar Pradesh, Delhi, Haryana and Chandigarh) are also likely witness above normal rain during this season while it would likely be below normal over the rest of adjoining North-West India (Rajasthan, Punjab, Jammu & Kashmir, Ladakh, Himachal Pradesh and Uttarakhand).

Better rain into monsoon

The situation will improve in April-June with above normal rain for Central India while pushing the deficit to the South Peninsula as well as Uttar Pradesh in North-West India. Rajasthan and Punjab too may return to normal while the hills of North-West India would continue to witness below normal rain.

The pre-monsoon and early monsoon phases (May-June-July and June-July-August) may see mostly above normal rain for the country as a whole (except Telangana and North Interior Karnataka in May-June-July) with the core monsoon months of June-July-August being particularly good all across when North Tamil Nadu and adjoining coast (including Chennai) may witness excess rain.

Published on February 25, 2021

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