There is a strong seasonal aspect to the monsoon caused by the path of the earth's orbit around the sun. This causes the high energy inputs of summer (where our pole is pointed towards the sun), and the cooling due to lower energy inputs in winter (when our pole is pointed away from the sun).
The degree and direction of the differential heating between land and sea is determined by the amount of solar energy reaching the earths surface. In summer the difference is greatest with the land surface warmer than the oceans. In the winter the ocean surface is warmer than the land, but the effect on winds due to this difference is less than in summer.
Since this heating in regulated by the position of the sun, their is a regular and predictible periodicity to this behavior. The regularity is due to the earths revolving around the sun in a predictible way to produce seasons. The variability of the seasons throughout the year is the easiest to predict. It is easy to say that every year, around June 1st, the summer monsoons will begin over Kerala India. There are other "scales of variability", both greater and less than a year, which are more difficult to predict because of their greater variability.
The Somali Jet is another interesting seasonal feature. It is the strongest persistent low lying jet in the world and it completely reverses direction twice a year. This jet is so strong that it results in a similar reversal in the ocean surface circulation. This is the only place in the world where the ocean surface circulation periodically reverses twice a year.