As the Bay of Bengal and Arabian Sea is still active, Monsoon withdrawal will commence in October. Monsoon when it makes onset and establishes and during the entire season, it is not only the rains which carry importance. There are many other changes and features that take place. All these features also retreat once we go into the withdrawal phase.
Some of these features that immediately bit adieu after Monsoon include:
During the Monsoon season, Pressure difference between North India and South India is very large. During withdrawal, the pressure gradient significantly reduces.
Secondly, high level winds over central and south India which come from the eastern parts are strong, during withdrawal they weaken, they become westerlies.
Thirdly, Tibet is a very important area for Monsoon. An Anti-Cyclone in Tibet area persists during the season, which defines the state of Monsoon, and during the withdrawal phase, even that feature also gets over.
The Inter Tropical Convergence Zone, also known as the ITCZ, which is a Monsoon Trough during Monsoon, during the time of retreat, shifts, and finally disappears.
For complete withdrawal, these features gradually have to retreat. The withdrawal officially begins on September 1 and lasts until October 15.
As far as the withdrawal commencement is concerned, absence in rains for five days, increase in temperatures, reduction in humidity and reduction in clouding is to be seen.
In terms of dates, there are large slippages for commencement, but withdrawal is complete by Oct 20 latest as Northeast Monsoon sets in by then and both Monsoons are not acknowledged at the same time. Withdrawal is seen only until 15 degrees North which includes all states and cities after Goa.
Unlike the onset of Monsoon, withdrawal is a speedy process for instance, in 2018, Monsoon withdrawal began on September 29, but by Oct 5, it was complete from North, Central, East and Northeast India.
Talking about Central India, it is a big portion consisting of Maharashtra, Madhya Pradesh and Chhattisgarh. Here, the withdrawal is not complete in a day or two but it is very common for Monsoon to retreat from this area in the middle of October.
Here is a table with date of withdrawal from central parts and complete withdrawal in the last few years.
This time, the withdrawal has been delayed, in view of formation of multiple systems. A Depression is expected to form in the Northeast Arabian Sea while a Cyclonic circulation already persists off Andhra Coast, and another low pressure area will form off Odisha coast. As long as the systems continue to move towards central parts, easterlies continue over North and withdrawal is not seen until then.
In fact, until Rajasthan continues to see easterlies, withdrawal process does not begin.
By this time in September, daily rainfall reduces to 4-5 mm. However, actual rainfall for the last two days have been 37 percent above normal yesterday and 60 percent above normal day before yesterday and will continue to be so.
The last low that will form will not move deep inside and will be close to the eastern parts only. Thus, by the time this system diffuses, conditions will become favourable for the withdrawal of Monsoon. Therefore, it looks like this year, Monsoon withdrawal will begin around the first few days of October itself.
News Credit: Skymet Weather