How is the monsoon known for its uncertainties?

The monsoon sometimes arrives too early or too late and is very irregular. This happens due to the following reasons:

i. When Western cyclonic disturbances from the Mediterranean Sea entering India from west and northwest gets delayed.

ii. Westerlies or Western jet stream which are formed parallel to Tibetan highlands got blocked by the Himalayas.

iii. Any disturbance to trade winds and ocean current disturbs the intensity and frequency of monsoon.

Note: Western and Central Asia remains under the influence of westerly winds along the altitude of 9-13 km from west to east. These winds blow across the Asian continent at latitudes north of the Himalayas roughly parallel to the Tibetan highlands.