According to Skymet Weather, there are three criteria for declaring the commencement of withdrawal of Monsoon. To begin with, it is the cessation of rainfall for continuous five days. This is followed by the establishment of an anti-cyclone and considerable reduction in moisture content.
West Rajasthan is the first post in the country to witness the retreat of the Monsoon, which also happens to be the last place for Monsoon to arrive.
At present, only the first criteria of rainfall has been met as there has been no rain over West Rajasthan during the last many days. But, winds are still blowing from southwest direction over any parts of Rajasthan, particularly over West and South Rajasthan. Due to this, levels of moisture are still very high.
Moreover, a fresh cyclonic circulation has also formed over Gujarat region. Thus, southwesterly winds will continue over the region for the next few days.
In addition to this, we also need to wait and watch the development of the anti-cyclone over Central Pakistan and adjoining West Rajasthan.
The weather models are indicating that the remaining criteria will start appearing gradually by the next week but it is too early to predict the actual date for the withdrawal of Monsoon.
As reiterated by Skymet Weather, the official date for the commencement of withdrawal of Monsoon season is September 1. However, there has been wide fluctuation in the dates for the beginning of the withdrawal of Monsoon every year.
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Any information taken from here should be attributed to skymetweather.com