What are the causes for good rainfall and longer dry spells during the rainy season or the advancing monsoon?

(i) When the axis of the monsoon trough lies over the plains, rainfall is good in these parts. On the other hand whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains and widespread rain in the mountainous areas.
(ii) The frequency and intensity of tropical depressions too, determine the amount and duration of monsoon rains The depressions follow the axis of the monsoon trough of low pressure.