El Nino and La Nina are the opposite phases of ENSO. They are part of the natural climate system and appear in the tropical Pacific every 3-7 years. Both, El Nino and La Nina are coupled phenomenon – means atmosphere and ocean are coupled in the tropics. It also means that if the ocean temperatures, current, or sea level changes, the atmosphere responds to it. Similarly, if air temperature, atmospheric pressure or winds change, the tropical oceans respond to it.
ENSO: Bureau of Meteorology-Australia has already announced ENSO Neutral conditions. However, their threshold for neutral is +/- 0.8°C. The Climate Prediction Center ( NOOA) has the threshold standard at +/- 0.5°C. As per CPC, the El Nino is transitioning towards ENSO-neutral. The ongoing event of El Nino which began in June last year, has weakened significantly. By June 2nd -3rd week, neutral ENSO conditions are likely. Historically, ENSO – neutral phase preceded by strong El Nino is generally short & sweet. Thereafter, La Nina conditions are expected to emerge and its impact could be effective from July end/ August beginning. Typical of La Nina, it saves monsoon season from the drought and below normal rainfall. On few selective occasions, the seasonal rainfall has been in excess. Over 90 % occasions, the seasonal rainfall ends on a normal/above normal note, predominantly remaining 100-105 % of LPA.
Sea surface temperature (SST’s) in the Central Pacific have been steadily cooling since Dec 2023. This surface cooling is supported by a significant amount of sub-surface cooling in the Central and Eastern Pacific. There is no change in the Nino indices, across the region, during last week.
IOD: The Indian Ocean Dipole is currently neutral. The index has remained below the threshold value (+0.4°C) for the last 4 weeks, albeit there is a marginal rise during the last week. The latest weekly value of IOD was +0.38°C, on 26 May 2024, as against the previous week value of +0.2°C. There is no likelihood of any spike in this mark and the index may cross the threshold marginally, by June end.
MJO: The Madden-Julian Oscillation strengthened and propagated eastward over the Indian Ocean during the latter half of May. Now, it is likely to shift further east over the Maritime Continent in Phase-4. It is likely to meander there, till middle of June. Tropical Cyclone genesis is likely in the South China Sea during second week of June. No major system is expected in the Indian Seas during first 10 days of June.
Monsoon onset has been announced over Kerala and Northeast India. While northeast region will rain adequately during next one week, monsoon progress over southern and central parts may not be as desired. The pace of monsoon and the intensity & spread may remain weak during first week of June.