‘Normal’ monsoon ends with rains at 99% of LPA

NEW DELHI: The monsoon season will officially come to an end on September 30, even as widespread and heavy rain continue over different parts of the country. In aggregate, it has been a good year, with monsoon rain amounting to 99% of the long period average (LPA) as on Wednesday (with a day to go), making it a “normal” monsoon year, according to India Meteorological Department.

Rainfall between 94% to 106% of LPA is considered normal by IMD. The LPA is considered for the period of 1961 to 2010 and is 88 cm. But it has not been a normal monsoon in terms of the pattern and distribution of rainfall. The most active monsoon month this year, in terms of rainfall, was September -- a month when the monsoon usually starts withdrawing. The numbers speak for themselves: there was 9.6% excess rain in June; 6.8% deficiency in July; 24% deficiency in August; and 31.7% excess rain in September.

The monsoon usually starts its withdrawal from northwest India on September 17. This year, several parts of the country are recording intense rain spells even towards the end of the month due to formations of cyclonic circulations, a deep depression and cyclones.

The first deep depression of the season was formed on September 13. Another depression formed over east-central Bay of Bengal on September 25 which later intensified into Cyclone Gulab and crossed the north Andhra Pradesh - south Odisha coasts on Sunday evening. A remnant of Gulab is likely to reach the Arabian Sea on Thursday and further intensify into cyclone Shaheen by Friday, according to IMD’s forecast.

No depressions were formed between June and August, a period that usually sees five to six; the depressions bring extensive rainfall to central and west India.

As on Wednesday, there was a 1% deficiency in monsoon rain since June 1 with 11% excess over South Peninsula; 3% excess over central India; 4% deficiency over northwest India; and 12% deficiency over east and northeast India. There was an 8% deficiency at the end of August which was recovered almost entirely in September.

The reason for rainy September was active weather conditions in the West Pacific and a favourable Madden Julian Oscillation (MJO), supporting convective activity and cloud formation over the Bay of Bengal. MJO is an eastward moving disturbance of clouds, rainfall, winds, and pressure that traverses the planet in the tropics and returns to its initial starting point in 30 to 60 days, on average, according to National Oceanic and Atmospheric Administration.

“The West Pacific was very active and remnants from there were moving towards Bay of Bengal leading to formation of depressions, a number of cyclonic circulations and one cyclone, Gulab which brought widespread and heavy rain to east, central and west India. A trough was also passing from Bay of Bengal to the Pacific where cyclonic circulations and tropical storms are forming one after the other which has started disintegrating now. MJO will also move into an unfavourable location leading to gradual reduction in convective activity,” explained Sunitha Devi, in charge of cyclones at IMD. But intense spells of rain will likely to continue over India’s west and east coast for another two, three days.

IMD’s extended range forecast shows reduction of rainfall activity from October 7. The monsoon is likely to begin its withdrawal from October 2-3, said Mahesh Palawat, vice president, climate change and meteorology, Skymet Weather.

DS Pai, scientist and head of climate research and services at IMD Pune said that though the monsoon hasn’t withdrawn, the rain recorded after September 30 will be counted as part of the post-monsoon season.