Skymet weather

Warm Pacific Underpin Strong El Nino, Indian Ocean Dipole Holds Light Positive

April 29, 2023 1:30 PM |

Climate models are extending enough caution of a potential El Nino developing during 2nd  half of the year. Models also read its peak during the later half of the Indian Summer Monsoon, more precisely during the quarter July-August-September. Though, the 'spring barrier' triggered low accuracy of the model does throw surprise sometimes, the pattern of  Pacific Ocean warming seems to be increasing the risk of strong El Nino, developing earlier than expected. Some models are raising the probability of an extreme or Super El Nino, albeit towards the fall of the year. The last extreme El Nino in 2015-16 pushed the global temperatures to the highest on record. Warming on account of El Nino was also fortified under the shadow of human-induced climate change. The year 2016 remains the hottest on record under the combined influence of rudimentary factors.

ENSO:  El Nino threshold is likely to be crossed by June 2023. The Climate Prediction Center (CPC) of NOOA considers El Nino conditions to occur when the monthly Nino 3.4 sea surface temperature departures meet or exceed + 0.5 Degree Celsius, along with consistent atmospheric features.  However, the Bureau of Meteorology- Australia, considers El Nino threshold at + 0.8 Degree Celsius.  The anomalies must also be forecasted to persist for 3 consecutive months. Some of the typical precursors of this event are currently in place. The central and eastern Pacific indices have crossed the threshold value and the other indices ( Nino 4 & Nino 3.4 ) have also had incremental gains. The westerly wind anomalies along the equatorial Pacific are anticipated to further warm the Nino regions across the board. 

The ENSO forecast plume indicates the onset of El Nino during May-June- July (73% chance). Continuation of El Nino is forecasted with increased chances of 83% in Jun-Jul-Aug and rising further to 87% in Jul-Aug-Sep.

The red colour shows positive IOD and the greenish blue denotes negative IOD

IOD:  The Indian Ocean Dipole is currently neutral. The IOD index value for the week ending 23 April 2023 was  +0.04 degrees. This has dropped from its earlier mark of +0.38 degrees on 20 Mar 2023. Most climate models are suggestive of a +VE event developing during the monsoon season.  Last year, the -VE IOD event was guised by strong La Nina and the monsoon ended with above-normal status. The hat trick of -VE IOD  has raised the chance of DMI (Dipole Mode Index ) being +VE during monsoon 2023. The IOD forecast generated at this point in time is not very accurate and needs to be observed later on cessation of the spring barrier. 

MJO:  Madden Julian Oscillation is now positioned over the equatorial Indian Ocean, albeit with decreased amplitude. It is unlikely to trigger any major convection over the Indian seas. Further, it is moving away towards Maritime Continent in phases 4 & 5.  Its amplitude is steadily growing and emerging out of the inner ring. Being far away from the area of operation, it is unlikely to assist the monsoon stream over the Bay of Bengal, which normally happens anytime after mid-May.

The key atmospheric variables are currently indicating ENSO  neutral conditions. The Southern Oscillation Index (SOI) was last placed at -0.7, yet another favourite of El Nino. Low-level easterly winds have weakened in the central and western tropical Pacific and have become westerly in the eastern Pacific. The likelihood of El Nino conditions is highly favoured with probability ranging from 82% to 87% during the Northern Hemisphere summer and autumn.

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