Indian Weather Man (IWM)

Special Monsoon Watch for August:-
Deviating from the routine, This additional MW has become necessary due to the SW Monsoon's poor performance in June and July 2012.

Seasonal Rainfall from 1st June - 31st July 2012;
Indian Regions:
NE  -10%  NW  -36%  Central  -15%   South Peninsula  -23%
India: -19%.
Analysis of India as a whole shows: 89% of India is in the deficient range (deficient range is -1% and above. Not -20% as taken by IMD.).The best performance yet is Sikkim and adjoining W.Bengal at +16%.
11% are in the normal range. (Normal means actually in the positve range).
Most deficient is Saurashtra and Kutch at -79% followed by Punjab at -67%.

What has gone wrong this year?

The reasons for deficient rainfall could be attributed to the late arrival and subsequent weak monsoon conditions over the country, the axis of monsoon trough remaining shifted to the north of its normal position, and non-occurrence of low pressure areas (or land lows) across the country.

Also, uneven spatial and temporal variability within the season may result in deficits in the seasonal mean all-India rainfall (AIR) which can have profound social and economical consequences.

What actually plays an important part for a good Monsoon?

The years 1965 and 1972 were years of severe drought over India and its surrounding area. The dynamical and thermal features of these seasons are contrasted with those of the normal monsoon. The main local abnormality during drought years is the shift of the monsoon trough northwards and the development of anticyclones over central India in the lower troposphere.

Drought years are associated with lower chances of low pressure areas to intensity into depressions, less westward movement, more horizontal extent, intense pressure departure from normal in comparison with flood years. However, more monsoon disturbances tilt significantly during flood years. The rainfall associated with these disturbances is highly variable and does not depend on the intensity, horizontal and vertical extent of the individual system. More number of lows intensify into depressions during strong monsoon conditions compared to those of weak monsoon conditions. Lows and depressions during strong monsoons have more westward movement and longer life period. Generally, very few lows form during break monsoon and none of them intensify into depression.
Hence, the presence of mid-tropospheric heating during strong and weak monsoons is essential for the formation of depression.

Parameters that will influence the August Rainfall:
The main and holding parameter is the location of the Monsoon Axis (Trough). Depending on the alighnment of this axis, the following vary and fluctuate:

Read the full article and the expectations for August on Vagaries.

Compiled by Rajesh and Rajan.