According to ENSO forecast issued by International Research Institute (IRI), ENSO-Neutral conditions are forecasted for next three overlapping 3 months seasons with 83% chances in Jun-Jul-Aug, 64% in Jul-Aug-Sep and 51% in Aug-Sep-Oct 2024, while chances of La Nina are 13%, 32% and 44% respectively. La Nina onset is unlikely before August 2024 and most likely in the quarter Sep-Nov 2024. Thereafter, La Nina remains the most likely category for the remainder of the forecast period ( till winter season 2025 ). At longer leads, the skill of the models degrades due to plausible changes in the initial conditions and variations of model physics.
ENSO: Equatorial Sea Surface Temperatures (SST’s) are above average in the west-central Pacific Ocean, near average in the east-central and below average in the far eastern Pacific Ocean. Over the last couple of months, negative sub-surface temperature anomalies have persisted in the eastern equatorial Pacific Ocean and extend to the surface. The central Pacific Ocean is largely near average, except for below average temperatures at depth.
The SST anomaly for Nino 3.4 during the Mar-Apr-May 2024 season was 0.79°C. For the month of May 2024, it was +0.31°C and for June 2024, it has dropped to +0.15°C. However, the most recent weekly value for the week ending 02Jul2024 was +0.4°C. It shows that El Nino conditions are ending but not without the last minute resistance. The residual effect of the exiting El Nino is still visible on global temperatures and Pacific Ocean, as well. Temperature anomaly of +0.4°C remains close to the positive threshold value and therefore may further delay the arrival of La Nina.
IOD: The tropical Indian Ocean usually witnesses a dipolar pattern of SST anomalies, which is commonly referred to as the Indian Ocean Dipole (IOD). The IOD phenomenon has received much attention due to its profound global impacts, yet its seasonal prediction remains a large challenge for the climate community.
Typically, La Nina events are accompanied by negative IOD-related SST anomalies in the tropical Indian Ocean (manifesting -ve SST anomalies in the tropical western Indian Ocean and +ve SST anomalies along the Java-Sumatra coast ).
The IOD index is currently neutral. The latest weekly IOD index to 30thJune 2024 was -0.4°C. The index value has plunged below zero in the last 4 weeks and literally collapsed from -0.09°C to -0.4°C during last one week. The index has now touched the negative threshold of -0.4°C. These values are in sync with the La Nina conditions likely during next month.
MJO: The Madden-Julian Oscillation, which remained incoherent in June is showing signs of renewed activity over the Indian Ocean in the first week of July 2024. The MJO pulse is likely to maintain a slow phase speed and also low amplitude over the Indian Ocean till mid-July. It is unlikely to support formation of powerful monsoon system over the Indian seas. The circulation pattern does favour cyclone formation across South China Sea and Philippines Sea during 2nd week of July and the probability increases further in the 3rd week.
Unlike the Atlantic basin, the Western Pacific can produce cyclone year-round but the bulk of activity happens from May through October. The latest date of record for seeing the basin’s first cyclone is June 8, 1983. The West Pacific has been quiet so far, this year. 2024 Pacific typhoon season seems to be on track to rank amongst slowest start for tropical cyclone activity.
The hangover effect of El Nino is still continuing. La Nina may not roll in before mid-August. Projection of weak or negative IOD leaves ripples on the seasonal prospects during the core monsoon month of July. La Nina and IOD, necessarily need to align and work in tandem to pull out a bountiful monsoon 2024.