The southwest monsoon had a late start, by about a week, with its appearance over the southern parts of the Bay of Bengal and the Andaman Sea. As far as onset over the mainland is concerned, the onset over Kerala took place on 5 of June instead of the normal date of 1 June. Late onset over Kerala, considered to be the entry point of the monsoon for the mainland of Indian subcontinent, was predicted successfully by IMD by applying a statistical model. After its onset over Kerala the monsoon advanced over southern parts of peninsula reaching upto Goa along the west coast by 8 June, where it got stalled for nearly 8 days.
Monsoon advanced into the northeast on 16 June, where it was late by about 2 weeks. Such delay is not very common, as since 1960 there are only four cases of similar late onset over NE India, occurring in the years 1979 (23 June), 1981 (17 June), 1983 (20 June) and 1986 (16 June).
With strengthening of monsoon flow over the Arabian Sea from 16 June onwards, monsoon progressed gradually along the west coast but the rainfall activity remained confined to the west coast only. A new surge in the monsoon flow has improved the rainfall scenario in the last week. Monsoon has covered most of the country as on today.
Since the onset/advance of the monsoon was delayed, the rainfall and its associated activity was also subdued over large area of the country upto 22 June when the country registered a rainfall deficiency of 49 percent. A very large portion of the country north of about 15º N, received deficient/scanty rainfall. But the Indian region south of 15º N, including the Islands, received excess/normal rainfall. As predicted by IMD, there was conspicuous improvement over central parts of the country particularly in Madhya Pradesh and Gujarat during last 4 days where rainfall position changed from scanty category to normal one. The overall rainfall deficiency has now come down from 49% as on 22 June to 35% as on today.
Causes of delay and rainfall deficiency
The delay in advance of monsoon has been mainly due to the interference of high latitude circulation features with the monsoon flow. The rainfall deficiency is largely due to the late onset/advance of southwest monsoon. The late entry of monsoon in the eastern parts and occurrence of prolonged severe heat wave conditions in these regions were because of penetration of dry continental air into these regions along the periphery of a high pressure area situated over central parts of India. With the advance of monsoon the heat wave conditions have abated.
There are signs of cyclogenesis taking place in the northwest Bay. This is likely to further strengthen the monsoon scenario over the country. Monsoon trough has got organised and is well placed upto mid-troposphere. Rainfall activity has already improved over central and northwestern parts of the country. It is likely to improve further. There may also be increase in rainfall over northern parts of peninsula. Showers are likely to decrease over northeast.
In the last more than 100 years, there were a total of 12 years when the June rainfall was deficient by 30 percent or more; and out of these 12 years, 10 years turned out to be normal monsoon years. Going by these statistics, the probability of this year turning out to be a normal year is very high as predicted by IMD's long range prediction model.