IMD extends date of South-West monsoon withdrawal by 3 days to October 10

India Met Department (IMD) has pushed back by three days to October 10 the date of expected withdrawal of the South-West monsoon, the most delayed since it began making a record of the dates.

Earlier, the national forecaster suggested in an extended outlook that the withdrawal could likely begin  on October 7 from the western parts of  Rajasthan.

The normal date of of withdrawal is September 1. The most delayed withdrawal in the past years has been recorded in 1961 (October 1) followed by September 30 in 2007.

No signs yet

There is no sign of monsoon withdrawal  during this week, concurred Jatin Singh, Managing Director of private forecaster Skymet Weather.

Bihar and the adjoining regions of East Uttar Pradesh and Jharkhand, which has been receiving some heavy rains last  week, will  get some respite from the intense monsoon activity, he said.

However, moderate rains are expected to continue over Bihar, Jharkhand and Bengal. The monsoon circulation over the central parts will also cause moderate rains over East Madhya Pradesh, Chhattisgarh and Odisha.

There have been bountiful rains over Madhya Pradesh this season, with record surpluses of 61 per cent and 24 per cent in West and East Madhya respectively.

Rajasthan, Punjab and Haryana will continue to experience light-moderate showers, which are likely to wane by the weekend. The wet spell over Gujarat is likely to continue for at least the first two days of the week.

Gujarat has experienced a record surplus of 39 per cent and all its pockets have received widespread and excess rains, Singh noted.

New milestones

The monsoon, meanwhile, has seen a number of other records being made this year, the IMD said in a detailed review at the end of what has been an exceptionally productive season.

After 1994, (110 per cent of long-period average, or the LPA), the rainfall received during the 2019 season is the highest seasonal rainfall received by the country as a whole.

(The LPA is calculated on the basis of the mean rainfall during the four-month monsoon season over the 50-year period from 1951-2010. It works out to an average of 89 cm for the country as a whole).

During 18 of the last 19 years (2001-2019), North-East India  received less seasonal rainfall  than LPA with  the exception of 2007 (110 of of LPA), the IMD observed.

This indicates that the seasonal rainfall over North-East India is passing through a below normal epoch like it was during the early 1950s to mid-1980s.

Also, after 1931, this is the first time that the seasonal rainfall is more than the LPA even after the June rainfall deficiency, which was more than 30 per cent of LPA.

After 1996 (119 per cent), 2019 saw the highest recorded rainfall for the month of August (115 per cent). It also made for the second highest September rainfall (152 per cent) after 1917 (165 per cent).

After 2010, this is the first time that rainfall during all the last three months (July to September) is above the LPA. It also saw the second highest rainfall during August-September (130 per cent) after 1983 (142 per cent).

In spite of  the late onset and a large deficient rainfall during  June, the seasonal rainfall has ended in above normal category with 110 per cent, the IMD said. Rainfall during July, August and September were 105 per cent, 115 per cent, and 152 per cent of the LPA respectively.

El Nino and IOD factors

The IMD had stuck to its forecast of a normal rainfall (96 to 104 per cent) for the season despite several global models indicating a strong possibility of an El Nino episode and possibly a below normal monsoon.

The quantitative forecast for the seasonal rainfall issued in April and May was 96 per cent of LPA with a model error of ± 5 per cent and ± 4 per cent of LPA respectively.

While issuing the forecasts, based on IMD’s models, it was suggested that the El Nino episode will weaken further and a positive Indian Ocean Dipole (IOD) event will emerge in the Indian Ocean.

The positive IOD, in which the western basin of the Indian Ocean warms up anomalously relative to the East, has  coincided with a productive South-West monsoon in the past.

Moreover, IMD had also predicted that the monsoon performance would be better in the second half of the just concluded season compared  with the first half.

The IMD’s analysis on weakening of El Nino and development of a positive IOD and the second half monsoon rainfall being above normal have thus proved correct.

However, quantitatively, the realised rainfall during the second half was more than predicted. The forecast for monsoon onset over Kerala (June 6 as against the actual onset on June 8) also proved off-mark

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