Mathematical rain forecasts

Understanding of monsoon rain formation based on valid mathematical basis is the first step in the quest for rainfall prediction.
The monsoon is here; soon, most places in the country would start receiving rainfall. Every year, its forecast is the subject of public discussion. The Meteorological Department issues two long-range forecasts: one in April, and the other towards the end of May or start of June. In the first, it gives the forecast of the quantity of rainfall the country as a whole is