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The Climate Prediction Centre of the US National Weather Service has hinted that the monsoon onset date of June 6 proposed by India Met Department (IMD) along the Kerala coast represents a more realistic assessment of the event.
The IMD has set June 6 as the day of the onset over Kerala while private forecaster Skymet Weather has advanced it by two days to June 4.
Delay in onset
The main question at this time is how quickly an active (wet) phase of an onset-facilitating Madden-Julian Oscillation (MJO) wave would re-emerge over the Indian Ocean, the US agency said on Wednesday.
The MJO wave is a global band of lower pressure, convection (cloud-building) and rainfall travelling from West to East periodically with implications for weather over the region it passes.
Cause for delay
The US agency held that the current suppressed (dry) phase of the MJO would likely presage below-average rainfall across the Arabian Sea, the Indian subcontinent, the Bay of Bengal and parts of South-East Asia until June 4.
“The suppressed phase of the MJO phase and related anomalies.... are expected to delay the onset of the Indian monsoon by perhaps next two weeks (May 22 to June 4),” it added.
Additionally, above-average temperatures are likely to accompany the suppressed convection across much of India and South-East Asia during this period.
The European Centre for Medium-Range Weather Forecasts predicts eastward propagation of the MJO signal across and the West Indian Ocean during this period, and its gradual weakening during the second week (May 29 to June 4).
The Global Ensemble Forecast System predicts slower eastward propagation across Africa during the ensuing two weeks, though with considerable spread apparent among ensemble members for during the second week.
IMD model
The Climate Forecast System model predicts rapid eastward propagation of a moderate MJO wave during the first week (May 22 to 28), and its deceleration over the West Indian Ocean during the second.
The IMD’s own coupled operational model for extended range forecast says that MJO wave would steadily weaken from Friday (May 24), reactivate during June 1 to 4, but weaken again into the second week of June.
In the meantime, pre-monsoon thundershowers will help cap the temperatures over the South Peninsula, especially over South Interior Karnataka, Kerala, Tamil Nadu and Puducherry.
On Wednesday, conditions remained favourable for the progress of monsoon beyond the South Andaman Sea and adjoining South Bay where it made a timely onset on Saturday (five days ago).
The IMD has forecast heavy to very heavy rain with extremely heavy falls over Assam and Meghalaya on Thursday, heavy to very heavy rain over Nagaland, Manipur, Mizoram and Tripura, and heavy over the Andaman & Nicobar Islands.
Intense heat is predicted for Vidarbha and slightly less intense heat for Telangana, Rayalaseema, Madhya Maharashtra, Marathwada, Madhya Pradesh, Chhattisgarh, East Uttar Pradesh, Odisha, Jharkhand and Tamil Nadu during the day.
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