It is November and the ENSO-Neutral conditions continue, unabated. There is no sign of positive IOD; rather it is turning strongly negative. Most global agencies got the La Nina forecast wrong this year. US’s National Oceanic and Atmosphere Administration (NOAA) issued a La Nina watch in May 2024, indicating that La Nina conditions are expected over the subsequent three months. Even, the National Weather Agency forecast in May confirmed that La Nina conditions would establish during the second half of the southwest monsoon, along with positive Indian Ocean Dipole. Actually, this was the base for predicting above-normal monsoon in 2024. Neither of these happened. Positive IOD got totally scrapped and La Nina still remains a distant dream.
The probability of La Nina got dropped from August to September and further got lowered from September to October. Also, it is a firm finding now that La Nina will be a weak and short event, this season. The possibility of having a ‘no show’ looms large. La Nina and El Nino events have periodicity. These patterns bring predictable changes in ocean temperatures and disrupt the normal wind and rainfall pattern across the tropics. These changes in the seasonal climate of the world’s biggest ocean have cascading global side effects.
ENSO: Unlike the US, where El Nino and La Nina have very little impact on summer climate, their strongest influence occurs in winters. La Nina favours below-normal hurricane activity in the eastern Pacific and above-average activity in the Atlantic, where the storms become more frequent and intense. Storms like Debby, Helene and Milton, evolving in the Gulf of Mexico were devastating systems. And now, another hurricane, after smashing the Caribbean has entered the Gulf of Mexico. Mercifully, the storm will weaken and steer away from the Florida coast.
La Nina in winters cause the Jet Stream to move northward and weaken over the eastern Pacific. During La Nina winters, the South sees warm and drier conditions than usual, in the US. The North and Canada tend to be wetter and colder. A similar pattern is true for the Indian sub-continent in the winter months.
During the last four weeks, negative SST anomaly changes were evident across most of the equatorial Pacific. In the east-central Pacific, some positive changes were interspersed with the negative ones. The Nino 3.4 index, the marker of ONI, has collapsed yet again. The index value for the week ending 04 Nov 2024 was -0.2°C, much above the earlier threshold mark of -0.5°C, recorded on 28 Oct 2024. SST anomaly has increased all along the equatorial Pacific, the exception being Nino 1+2, which, as such is having large fluctuations over the past 6 weeks. At this pace and with these records, La Nina is unlikely to come up in November. There is a strong possibility of missing this event in 2024.
IOD: The Indian Ocean Dipole is neutral. The IOD index for the week ending 03 Nov 2024 was -0.7°C, making it the sixth consecutive week, close to or below the negative IOD threshold (-0.4°C). All climate models indicate the IOD index will meet or exceed the negative IOD threshold in Nov-Dec, before returning to neutral value, early next year.
MJO: The Madden-Julian Oscillation is currently positioned over the Western Hemisphere and Africa region with a moderate amplitude. The pulse is likely to weaken and steadily shift over the Indian Ocean in the third week of November. The MJO evolution favours tropical cyclone development over the southwestern Indian Ocean, north of Madagascar and a little away from the Mozambique channel. There are no early indications of any tropical cyclone over the Indian Seas till the third week of November.
The CPC ENSO outlook forecasting La Nina onset in Sep-Nov, with a 60% chance will go wrong. The IRI model-based ENSO outlook forecast is likely to score over the CPC. This forecast indicates a continuation of ENSO-Neutral conditions for Oct-Dec 2024(53%chances). This objective forecast also shows weak and short-lived La Nina conditions, manifesting genuinely early next year. Both, the CPC and IRI outlooks indicate the return of ENSO-Neutral condition in the boreal spring of 2025.
Image Courtesy: NOAA and CPC
