La Nina's wait is getting longer. Uncertainty still hangs around. The Oceanic Nino Index (ONI) for the quarter Oct-Nov-Dec (-0.4°C) has inched closer to the threshold mark of -0.5°C. After the devolution of El Nino last year, the sea surface temperatures in the eastern and central Pacific became mostly near-to-below average during the quarters Jun-Jul-Aug to Aug-Sep-Oct. Recently, below-average SSTs were evident across the equatorial Pacific in the Nino region. This pattern was a typical transition from El Nino to ENSO-Neutral and potential La Nina. However, the Nino indices have not remained steady for the last about four weeks. The Nino 3.4, marker index for ONI has once again changed track to lower its guard. The Southern Oscillation Index (SOI) on the other hand is strongly driving the atmospheric conditions to La Nina. The lack of resonance between the ocean and atmosphere indicators has led to a delay in the emergence of La Nina.
ENSO: Though, the cause of an ENSO warm or cool event is not fully understood, the two components of ENSO – sea surface temperature and atmospheric pressure are strongly related. The presence of either of them sufficiently modifies the general flow to affect normal weather conditions in different parts of the world.
The volatility of Nino indices in the tropical Pacific has been a concern for a while now. Stabilization of these indices in general and the marker index Nino 3.4 in particular, is very essential. Nino 3.4, after speedy gains from -0.3°C to -1.1°C in four weeks has dropped yet again, this week. The weekly value of the index as of 06th January 2025 was -0.7°C. The other indices have also warmed across the central and equatorial Pacific. Certainly, this is not a good sign for the evolution of the long-awaited La Nina.
IOD: The Indian Ocean Dipole is neutral and is following a typical behaviour observed at this time of the year. The index, which was tending negative from mid-Oct, returned to neutral at the start of Dec 2024. The IOD is within limits of negative neutral and may turn zero-zero during this month The latest value of the index for the week ending 05thJan 2025 was -0.16°C.
MJO: The Madden-Julian Oscillation is propagating eastward from the Western Hemisphere to the Indian Ocean, with augmented amplitude. The return of active MJO to the Indian Ocean is expected to strengthen the cyclone genesis potential for the Southern Indian Ocean. The tropical storms may come up close to the Mozambique Channel (Madagascar) and Timor Sea (North Australia). The equatorial belt, north of the equator over the Indian seas will also find enhanced convection but will keep a safe distance from mainland India. Sri Lanka and Maldives may get heavy weather activity during the third week of Jan 2025.
Negative surface and sub-surface temperature anomalies in the central and eastern Pacific are indicators of La Nina. However, these timings are very unusual and defy the historical timelines. The typical inception of La Nina is bound to lower the authenticity of ENSO status for the remaining period of the forecast.
