Moderate El Nino conditions persist in the central-eastern equatorial Pacific Ocean. Important oceanic and atmospheric indicators remain aligned with an ongoing El Nino event, which of course is gradually diminishing. Also, the atmosphere indicators have gone mild, as compared to past El Nino events of similar magnitude. The traditional Southern Oscillation Index currently falls in the ENSO-neutral range with the last recorded average value of +0.5 for Jan 2024. The latest value, as of Feb 2024, will be available next week.
An El Nino advisory from the Climate Prediction Center continues for the month of March, alongside a La Nina ‘watch’ issued for June to August 2024. La Nina watch means conditions are favourable for the development of La Nina with a notice period of six months. As per CPC, ENSO-neutral conditions become the most likely category in April-Jun and May-Jul of 2024. For Jun-Aug 2024, no single category stands out as dominant, with ENSO-neutral and La Nina being equitable. By Jul-Sep, La Nina becomes the most probable category.
ENSO: El Nino forecasts before spring tend to be notoriously biased due to the spring predictability barrier. As the Sun transitions across the equator, from one hemisphere to another, the climate system becomes quite noisy in spring. During La Nina year, the tropical Pacific Ocean soaks up heat and builds up its volume of warm water. The currents contribute to forming a warm pool in Oceania, increasing rainfall in Asia and Australia. It lowers the temperature on the American coast and increases aridity.
Fluctuations are more in the Nino 1+2 region. Possibly, the proximity of land is influencing the heat potential of this region. Nino 3.4, the representative of the Oceanic Nino Index (ONI) is stable with the anomaly of +1.5°C for the second consecutive week. It has been observed that the cooling process slows down significantly after reaching the mark of 1°C. For ENSO-neutral, the ONI has to drop below +0.5°C.
IOD: The Indian Ocean Dipole is getting slashed at a rate faster than normal. Within the last 4 weeks, the index has turned negative-neutral from its earlier positive stance of 0.64°C, on 21st Jan 2024. The latest value of the index for the week ending 25 Feb 2024 was -0.22°C. It is likely to stay negative-neutral or close to zero-zero for the next about 4 weeks.
MJO: The Madden-Julian Oscillation had retreated into the unit circle, last week. However, the models indicate continued eastward propagation, with a quick phase speed over the Indian Ocean. It is likely to increase in amplitude, while in Phase 4&5 over the Maritime Continent. It may build up enough potential to circumnavigate the globe by the end of this month. Currently, there are no active storms, anywhere in the oceans. The tropical cyclone activity is likely to increase across the Indian Ocean with potential cyclone development, east of Madagascar.
The impact of El Nino is measured on a seasonal time scale and not in terms of individual small-scale weather events. Also, the El Nino impact doesn’t occur in isolation, anymore. Human-induced climate change overlaid on the Pacific warmth/cool may lead to regional extreme weather events in different parts of the globe. El Nino has been known to enhance the atmospheric river events in the Pacific West of the US. A little while back, California was deluged by back-to-back potent atmospheric river-fueled storms that unloaded record rainfall, triggering disastrous flooding in the region. El Nino takes the toll of the winter season over northern parts of the US too. Multiple states in the region experienced the warmest-ever December and an overall toasty January, with paltry amounts of snow; a trend that carried on in February, too.