After being trolled for faulty predictions about the monsoon arriving in Delhi, the India Meteorological Department (IMD) issued a clarification here on Monday on the advancement of southwest monsoon.
"The delay in monsoon advance was mainly due to (i) no formation of low pressure area over Bay of Bengal, (ii) No presence of monsoon trough at mean sea level near Delhi, (iii) 5-6 Western disturbances moved west to east across North India which dominated over the monsoon easterlies," it said.
The Met Department said Southwest Monsoon continued its advance over the country till June 13 in association with favourable atmospheric circulation and a low pressure system over Bay of Bengal after the onset of monsoon over Kerala on 3rd June.
Moisture laden easterly winds have led to increase in cloudiness and relative humidity. It also led to revival of monsoon over the region and occurrence of fairly widespread rainfall activity over east Rajasthan, HP, Uttarakhand, J&K and scattered rainfall over Punjab and west Rajasthan. However, it did not cause significant rainfall activity over Delhi even though, there was rainfall activity over neighbouring places around Delhi.
Rare and uncommon
Such kind of failure by numerical models in prediction of monsoon advance over Delhi is rare and uncommon, IMD said.
By June 13, it covered most parts of the country except northwest India. On June 13, numerical weather prediction (NWP) models suggested the favourable conditions with moist lower level easterly winds reaching to northwest India which may help further advance of monsoon into most parts Madhya Pradesh; remaining parts of Uttar Pradesh; Delhi; Haryana and Punjab during subsequent 48 hours. Accordingly, a press release was issued indicating likely advance of monsoon into Delhi by June 15.
On June 14, however, weather analysis based on satellite and NWP model consensus indicated approach of a trough in mid-latitude westerly winds, leading to weakening of easterly winds over northwest India. Due to adverse influence of this mid-latitude westerly winds, further advance of monsoon into remaining parts of northwest India including Delhi was not expected.
Accordingly, IMD issued an updated press release indicating that further advance of southwest Monsoon into remaining parts of northwest India including Delhi would be slow and delayed. However, this development of interaction with westerlies could not be anticipated by the weather prediction models.
Since June 20, there has been no further advance of monsoon due to weak/break monsoon conditions. On July 5, IMD said that monsoon would advance into remaining parts of West Uttar Pradesh, some more parts of Punjab, Haryana and Rajasthan and Delhi around July 10.
Accordingly, the moist easterly winds have spread into northwest India. After July 8, easterly winds at lower levels were established along the foothills and from July 9 onwards easterly winds were established over planes of northwest India.
