'Southwest Monsoon Arrival On May 31, Forecast Spot On Since 2005 Except 2015,' Says IMD

The national weather bureau has predicted that the South West monsoon will arrive -- a day ahead of its normal schedule -- on May 31. The meteorological office sought an error margin of four days, adding that it has never been wrong in the past 19 years. The Indian Meteorological Department(IMD) has been issuing operational forecasts since 2005, reports ETV Bharat's Saurabh Sharma.

New Delhi:The Indian Meteorological Department (IMD) said that the much awaited Southwest monsoon will hit the Kerala coast on May 31, which is a day earlier than its normal schedule of June 1.

Typically, the monsoon arrives at the Kerala coast on June 1 with a seven days margin of error. It progresses to the entire country in the next two weeks after its onset.

Southwest Monsoon

The Weather office in a paper on "New Normal Dates of Onset/Progress and Withdrawal of Southwest Monsoon over India", published in 2020, said most of the country receives 70-90% of its annual rainfall during the southwest monsoon season (June – September).

The paper said, "the initial monsoon rains are experienced in the month of May over south Andaman Sea and the monsoon winds then advance in a north-westerly direction across the Bay of Bengal."

It said the onset and duration of this main rainy season along with the quantity of rainfall play a crucial role in "the agricultural planning, food security, and the lives of around 25 crores strong labour workforce in the agriculture and allied sectors of the country."

The duration of the monsoon over many parts of the south Peninsula is more than 4 months. The duration halves when it prevails over the north-western parts of the country. Advance of the southwest monsoon over the Indian mainland is marked by monsoon onset over Kerala and is an important indicator characterising the transition from a hot and dry season to a rainy season, it said.

How Forecast Data Is Arrived At?

For this year's monsoon season, the IMD's projections suggest that the southwest monsoon will start in Kerala around May 31, with a potential error margin of four days. The weather office has been issuing operational forecasts for the date of monsoon onset over Kerala from 2005 onwards.

An indigenously developed state of the art statistical model with a model error of ± 4 days is used for the purpose, a senior IMD official said.

The six "Predictors" used in the models include Minimum Temperatures over North-west India, Pre-monsoon rainfall peak over south Peninsula, Outgoing Long wave Radiation (OLR) over South China Sea, Lower tropospheric zonal wind over equatorial southeast Indian Ocean, OLR over Southwest Pacific Ocean and upper tropospheric zonal wind over equatorial northeast Indian Ocean.

According to the weather office, its forecasts regarding the onset of monsoon have never been proved wrong in the last 19 years except in 2015.

"IMD’s operational forecasts of the date of monsoon onset over Kerala during the past 19 years (2005-2023) were proved to be correct except in 2015", the official said.

Last year, the onset of the monsoon was on June 8. In 2022, it was May 29 while it was June 3 in 2021, June 1 in 2020 and June 8 in 2019.

Heatwave Prediction In These States

According to the IMD, heat wave conditions are likely to hit isolated/some pockets over Gujarat Region on May 16-17, Konkan on May 16, Saurashtra and Kutch on May 16-17, over West Rajasthan during May 16-20, over Punjab, south Haryana during May 16-19 and north Madhya Pradesh, East Rajasthan, Uttar Pradesh, Bihar during May 17-19 May.

Similarly, heat wave conditions are likely to prevail in isolated pockets over Delhi, Jharkhand, Gangetic West Bengal, Odisha during May 18 -19.

The temperature in the national capital is likely to touch 45 degrees celsius over the weekend, the MeT department said.

The soaring mercury has been attributed to dry westerly and northwesterly winds, as well as clear skies leading to direct sunlight in northern states from Thursday.

Delhi Heatwave Forecast

Soaring temperatures are likely to prevail over Delhi, Haryana and Punjab over the next few days from May 17-19, with Delhi likely to witness its first spell of harsh heatwave this weekend.

The National Capital is yet to record a heatwave day as the maximum has not been more than 4.5° C above normal.

The temperature in Delhi and surrounding areas are witnessing temperatures hovering around 40° C, but it could touch 45° C on Saturday.

Rainfall Forecast In These States

Isolated heavy rainfall is very likely over Tamil Nadu, Puducherry and Karaikal, Kerala and Mahe, Coastal and South Interior Karnataka during May 16-20. It also predicts isolated very heavy rainfall to prevail over Tamil Nadu on May 18 -19 and Kerala on May 19.

Similarly, isolated light to moderate rainfall accompanied by thunderstorm, lightning & gusty winds (40-60 kmph) very likely over Konkan and Goa, Madhya Maharashtra, Marathwada on May 16 -17, over Madhya Pradesh, Vidarbha, Chhattisgarh, Odisha, Gujarat Region on May 16 while isolated hailstorm activity is likely to hit Madhya Maharashtra on May 16.

The weather office also predicts rainfall for the north-eastern states including Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura during May 16 -19 May. Additionally, isolated heavy rainfall was also likely over Arunachal Pradesh during May 16-19 and Assam & Meghalaya on May 17-19.

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