Tuesday, August 3: Amid the economic hardship across India due to the COVID-19 pandemic, the only silver lining has been the healthy monsoon rainfall last year and so far this year. After an excellent first half with just a 1% rainfall deficit, the Monsoon 2021 is all set to continue producing normal amounts of rains across the country in August and September, as per the recent forecast from the India Meteorological Department (IMD).
Rainfall over the country as a whole during the second half of southwest monsoon season is most likely to be normal with a tendency to be on the positive side of the normal, said the IMD Director General Mrutyunjay Mahapatra addressing a virtual press conference on Monday. As per the mod-season long-range forecast from the national forecaster, rainfall in August and September may range from 95 to 105% of the Long Period Average (LPA), while that in August is most likely to be 94 to 106 per cent of LPA.
The wet phase of Madden–Julian Oscillation (MJO) will be back over the Indian Ocean during the third week of August, leading to enhanced monsoon rainfall. But until then, the tendency will be a little below normal in general, except the very heavy rains for the next couple of days in Madhya Pradesh, explains Leon Brown, Head of Global Forecasting Operations at The Weather Company.
West Madhya Pradesh and East Rajasthan have been witnessing very heavy showers since last week and are forecast to witness similar weather conditions till Wednesday, August 4.
North, east and northeast may remain drier
As per the latest forecast, the overall rainfall across India would be in the normal range around the LPA of 428.3 mm, which is a 50-year rainfall average between 1961-2010. However, the spatial distribution suggests that below normal to normal rainfall is likely over many parts of the northwest, east and northeast parts of the country.
“It does look like the north of India will be a bit drier than normal for the 2nd and 3rd weeks in August, until the MJO kicks things off later in August. After that, the northeast and southwest may see a slight deficit, but the rest of the north should see a wetter period,” explains Brown.
Particularly regions like Delhi, Gujarat, North Rajasthan, Jammu and Kashmir, Ladakh, Punjab, Haryana, Bihar, Chhattisgarh, North Bengal, Meghalaya, Sikkim and Arunachal Pradesh may see substantial rainfall deficit in August and September.
Normal to above-normal rainfall is most likely over most parts of peninsular India and adjacent central India during the next two months, says the IMD forecast.
In August, below normal to normal rainfall is likely over many areas of central India and some areas over northwest India, while normal to above normal rainfall is most likely over most parts of peninsular and northeast India.
Monsoon situation so far
Since the beginning of the monsoon season, India has registered 465 mm rainfall on average till August 2, compared to the LPA of 470 mm. However, the ‘normal’ monsoon is not uniformly spread across the country. While some parts of the country still remain drier than normal, other parts, including Delhi and Mumbai, have witnessed repeated flooding episodes.
Regions like Konkan, Goa, Marathwada, Rayalaseema, Telangana, Tamil Nadu, north Karnataka, Haryana, Delhi and South Bengal have received excess rainfall of over 30%. At the same time, all the northeastern states, Gujarat, Kerala and Lakshadweep, have witnessed a deficit of more than 30%.
The IMD data shows that July month witnessed very heavy rainfall (115.6 to 204.5 mm) events at 567 stations IMD across India, while 112 stations witnessed extremely heavy rainfall events of more than 204.5 mm in 24 hours.
The updated long-range forecast by IMD on June 1 predicted a total of 101% of the LPA (with a model error of ±4%) for this monsoon season. The Weather Channel had also forecast that the total rainfall from June to September could accumulate up to 101% of the seasonal norm back in April.
“As the changes in the sea surface temperature (SST) conditions over the Pacific and the Indian Oceans are known to influence the Indian monsoon, IMD is carefully monitoring the evolution of sea surface conditions over these Ocean basins,” Mahapatra said. This year, the IMD has adopted a new strategy for issuing monthly and seasonal operational forecasts for the southwest monsoon rainfall over the country by modifying the existing two-stage forecasting strategy.
The new strategy is based on the existing statistical forecasting system, and the newly developed Multi-Model Ensemble (MME) based forecasting system. The MME approach uses the coupled global climate models (CGCMs) from different global climate prediction and research centres, including IMD’s Monsoon Mission Climate Forecast System (MMCFS) model.
IMD will issue the forecast for September month rainfall towards August end or the beginning of September 2021.
(With inputs from IANS)
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