The spring predictability barrier, the bugbear of weather forecasters during this time of the year, has continued to disrupt attempts by global models to arrive at an informed decision about a building El Niño in the tropical Pacific and its likely impact on weather during the ensuing Northern Hemisphere summer.
Models have a hard time making accurate forecasts during this period. The Climate Prediction Centre of the US National Weather Services put it succinctly; there are increasing chances of an El Niño at longer forecast horizons (next four-six) months, though uncertainty remains thanks to the lower forecast accuracy.
La Niña fading out
Neutral (neither La Niña or El Niño) conditions are expected to begin in the next couple of months, and persist through the spring and early summer, the US agency said. Some models continue to insist the ongoing La Nina (rain-friendly for India) is fading out, to be replaced by neutral conditions first, followed by an El Niño, even while citing the seasonal predictability caveat.
The caveat applies also to the forecast of the Indian Ocean Dipole (IOD) event that mimics the El Niño-La Nina transition nearer home for India. An El Niño can potentially thwart the annual June-September rainfall season (South-West monsoon), though with honourable exceptions. A concurrent positive phase IOD can neutralise the El Niño impact, as seen from past experience.
IOD carries caveat
The Application Laboratory of the Japanese national forecaster Jamstec, which discovered the IOD phenomena, said its forecast for a positive IOD this year has run up against the predictability barrier. The ‘La Niña-like state’ has started decaying, it said in its latest observations. Its SINTEX-F ensemble mean predicts an El Niño will occur in May, but there is uncertainty over its amplitude. The ensemble mean of its SINTEX-F2-3DVAR version predicts a relatively weak El Niño.
The Australian Bureau of Meteorology has said the average of international model forecasts suggest the ongoing La Niña may end by March and give way to a neutral phase in May. The El Nino may set in by July. As for the IOD, the neutral phase will peak in March, start showing a bias towards the positive IOD phase in May, before turning borderline positive IOD by July.
Differing rain outlook
The Busan, South Korea-based APEC Climate Centre said the tropical Pacific state is expected to change from neutral during March-April-May to El Niño during June-July-August. The El Niño intensity is expected to gradually increase from April-May-June to June-July-August. As a result, above normal temperatures are expected for most of the globe for March to August 2023.
It is against this context that February-based weather forecasts for the initial monsoon months of June and July for India need to be seen. The European Centre for Medium-Range Weather Forecasts appears to predict a normal monsoon with regional variations in above-normal and below-normal rainfall amounts from March to July, particularly during the monsoon months from June to September. These are initial forecasts and are subject to change. Predictions for August-September are awaited.
Normal rain predictions
The European agency also sees East and North-East India heating up above normal during the pre-monsoon months of March-April-May; and to a slightly lower extent over Gujarat, South-West Rajasthan and adjoining West Madhya Pradesh. Maximum temperatures are expected to be normal over the rest of the country across Peninsular India and adjoining North-West India. The Japanese forecaster has predicted normal rainfall for most of the country during March-April-May.
As for June-July-August, the Japanese agency sees below-normal rainfall for East India (foothills of Himalayas in UP, Bihar, East Madhya Pradesh, Chhattisgarh, Jharkhand, Odisha, West Bengal and parts of North-East India). It will be above normal for the rest of Madhya Pradesh, Maharashtra, Telangana, Andhra Pradesh and Karnataka) and normal for Kerala and Tamil Nadu.
Korean ‘red’ alert
The UK Met Office and the International Research Institute for Climate Society at Columbia University, too, have offered a benign outlook for May-June-July, suggesting normal rainfall for most parts of the country. July is the rainiest monsoon month for India, while August is the second rainiest.
In contrast, the South Korean agency draws a grim picture predicting below-normal rainfall for the entire western half of the country during this period across West Rajasthan, West Madhya Pradesh, Gujarat-Saurashtra, West and Central Maharashtra, Telangana, Andhra Pradesh, Karnataka, Kerala and Tamil Nadu. The rest of the country will likely see normal rainfall except in West Bengal.