The southwest monsoon had a late start this year. It entered the extreme southeast Bay of Bengal and south Andaman Sea on 26 May, with a delay of 11 days. An extensive cloud mass associated with Inter-Tropical Convergence Zone (ITCZ) drifted northwards in the extreme south Arabian Sea in the first week of June. It triggered the onset of monsoon over Kerala on 5 June. The late onset over Kerala was successfully predicted by IMD on 18 May by applying a statistical model. The monsoon advanced over the southern parts of the peninsula reaching upto Goa along the west coast by 8 June. At the end of this period the all India rainfall was deficient by 51%. The rainfall activity, however, remained confined to the west coast only. Its further advancement was stalled for 8 days and the all India rainfall deficiency at the end of 2nd week of June increased to 59%.
The delay in the advance of monsoon over the northeast and its stagnation along the west coast after 8 June had been primarily due to the interference of high latitude circulation features with the monsoonal flow. An anomalous anti-cyclonic circulation persisted over the central parts of the country during first half of June. The penetration of strong and dry continental northwesterly flow into the eastern parts of the country along the periphery of above said anti cyclonic circulation prevented the entry of monsoonal flow into the northeast and eastern parts of the country. The entry of these dry winds and the delay in the onset of monsoon resulted in severe heat wave conditions over the eastern and then over the northern parts of the country.
As the advancement of southwest monsoon is not a steady phenomenon and takes place in spells, a second surge in the monsoon came towards middle of June with the strengthening of south-westerlies both over the Arabian Sea and the Bay of Bengal when the monsoon advanced into the northeast on 16 June with a delay of about 2 weeks. Such delay in the advancement of monsoon into the northeast is not very common, as since 1960 there have been only four such cases viz. 1979 (June 23), 1981 (June17), 1983 (June 20) and 1986 (June16). With the advance of monsoon over the West Bengal & neighbourhood on 20 June, the heat wave conditions started abating from the eastern parts and abated from most parts of the country by 24 June.
A cyclonic circulation formed over eastcentral Arabian Sea on 16 June which moved northwards and concentrated into a depression over northeast Arabian sea and adjoining Saurashtra on 21 June. Under its influence the monsoon further advanced upto Saurashtra and south Gujarat on 21 June. The associated rainfall activity, however; still remained confined to the west coast only. The depression moved westwards and weakened into a low pressure area over northwest Arabian Sea on 23 June. With the weakening of the depression, the monsoon covered the entire peninsula and central parts of the country on 24 June. As on 22 June, the All India rainfall deficiency stood at 49%.
The third surge in the monsoon flow came in the last week of June when the monsoon flow over the eastern parts of the country organised further with the formation of a cyclonic circulation over north Bay of Bengal on 26 June which subsequently concentrated into a depression on 28 June over Gangetic West Bengal and adjoining Jharkhand. The formation of this depression and the consequent organisation of monsoon trough led to rapid advancement over the northern and northwestern parts of the country and covered the entire country by 30 June. It reached from East Uttar Pradesh to West Rajasthan in six days against a normal period of one month. Formation of this depression and organization of the monsoon trough led to extensive rainfall activity over the central parts of the country and all India rainfall deficiency has been reduced to 15% as on 30 June. The cumulative rainfall over the central parts of the country which was 22% of normal as on 15 June stands at 113% of the normal as on 30 June.
Since the onset/advancement of monsoon was delayed, the rainfall activity was also subdued over large parts 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 15=BA N received deficient/ scanty rainfall. As predicted by IMD, there has been a conspicuous improvement over the central parts of the country during the last week. The overall rainfall deficiency has now come down from 49% as on 22 June to 15% as on 30 June. The number of sub-divisions in deficient/scanty category has gone down from 28 as on 22 June to 17 as on 30 June. A number of sub-divisions in central India viz. Saurashtra & Kutch, Gujarat region, Rajasthan, East Madhya Pradesh, Madhya Maharashtra and Vidarbha have received normal/excess rainfall. Punjab and Haryana in northwest India have also received normal/excess rainfall.
The depression which formed over Gangetic West Bengal and adjoining Jharkhand now lies over north-east Madhya Pradesh and adjoining SE Uttar Pradesh near Reva. Also a mid-tropospheric cyclonic circulation lies over Gujarat & neighbourhood. The monsoon trough is at its near normal position and well organized extending upto mid tropospheric levels.
The prediction based on the numerical products of National Centre for Medium Range Weather Forecasting (NCMRWF), India Meteorological Department (IMD), Florida State University Super-ensemble model, USA; European Centre for Medium range weather Forecasting (ECMWF), UK; Centre for Ocean Land Atmosphere studies (COLA), USA; US Navy Model, USA etc, suggest that the depression is likely to move slowly in a north-westerly direction, weaken into a low pressure area after 2 days and then interact with an approaching western disturbance during 3-5 July,2005. Under the circumstances, the predictions indicate that while good rainfall activity over central India may continue for another 2-3 days, there could be increase in rainfall activity over NW India due to interaction of western disturbance during 3-5 July,2005. There are also indications of weakening of Mid-tropospheric circulation over Gujarat after 4th July, leading to decrease in heavy rainfall activity and hence easing out flood situation over the region. The sub-dued rainfall activity over NE States and Interior parts of south Peninsular India is likely to continue for another 3-4 days. With the above scenario of rainfall activity over the country, the overall rainfall deficiency for the country as a whole, is likely to decrease further.