The performance of Southwest Monsoon depends on a set of global complex parameters. Indications of which start arriving by December/January and goes on till just before the onset. Compilation of different parameters is carried out to assess stage wise performance of monsoon. The analysis of parameters up to March can give the initial stage of forecast. And based on data up to May we are able to make the season forecast including region wise performance.
Statistical Analysis
According to 100 year statistical analysis, no simultaneous years are drought years, except in 1965-1966 and 1986-1987. The deficit in 1965 was 16%, while in 1966 the monsoon was deficit by 12%. In 1986 and 1987 the monsoon was deficit by 12% and 17%, respectively. Therefore we don't expect 2015 to be a drought year as Southwest Monsoon was deficit by 12% in 2014, which is considered to be a drought.
El Nino
The heating of equatorial Pacific or the El Nino effect is another factor that plays a vital role in analyzing the monsoon performance. According to weather experts most of the El Nino years lead to drought in India. El Nino usually do not get extended more than 15 months as they taper and gradually fade out. The El Nino had started evolving in February last year but as of now it is receding so the threat of drought is rare and therefore hints towards a normal monsoon.
Pre monsoon heating
Peninsular India starts heating up by March and excessive heat over south and central parts of the country is considered good for the monsoon. If the heating is not good the performance of monsoon is affected, which is exactly what had happened in 2014.
Pre monsoon peak rainfall
With heat, thunderstorm activities also come up. Invariably peninsular India observes a peak pre monsoon rainfall which could be a precursor and decisive for the likely onset dates of Southwest Monsoon. The intensity and spread of rainfall during this time is reflective of the performance of the coming monsoon season.
Inter Tropical Convergence Zone
The Inter Tropical Convergence Zone is usually seen oscillating from the southern Hemisphere to the equator and then to the Northern Hemisphere. The ITCZ which is now south of Equator will shift north of equator in the month of March. ITCZ needs to sustain its intensity and keep showing progressive northward shift for a good monsoon. Any recession or retrogation may prove detrimental for the health of the overall monsoon performance.
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