What could be the possible reasons of the slower-than-expected progress of the western branch of the Southwest monsoon in 2019?

After the delay in the arrival, monsoon is progressing northwards. But it is still bringing less than expected rainfall. There has been a deficient by 36% compared to what is normal until this stage. It is unlikely to be made up in any substantial manner in the remaining days of the month

Factors responsible for deficiency

• The very severe cyclonic storm Vayu in the Arabian Sea hindered the advance of the monsoon. As a result monsoon lay centred over Kerala for nearly a week.
• Arctic burst during last winter resulted in severe cold including sub-zero temperatures across the globe. The remnant effects would be witnessed even in June impacting the monsoon rains.
• The extra-tropical circulation prevailing across lower latitudes over the Indian subcontinent and adjoining north Indian Seas (Arabian Sea and the Bay of Bengal) even after the onset of the monsoon resulted in conditions that were not supportive enough for the smooth inflow of monsoon currents blowing from the Arabian Sea.
• Warmer northwestern regions and a relatively cooler equatorial belt facilitate and pull over the monsoon currents from southern hemisphere across the Arabian Sea along the western coast towards the land. But the extra-tropical anomalies over the extreme northwestern region and the neighborhood left the entire region cooler, acting as a deterrent to the incoming monsoon winds.

As a result there was a slower-than-expected progress of the western branch of the Southwest monsoon.