The Onset of the Monsoon and Withdrawal

The Onset of the Monsoon and Withdrawal 

• The Monsoon, unlike the trade winds, is fluctuating in nature, influenced by the various atmospheric conditions encountered on its way over the warm tropical seas. The monsoon season lasts 100-120 days, from early June to mid-September.
• Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days. This is known as the ‘burst’ of the monsoon and can be distinguished from the pre-monsoon showers.
• The monsoon usually arrives in the first week of June at the southern tip of the Indian peninsula. It then divides into two branches: the Arabian Sea branch and the Bay of Bengal branch.
• The Arabian Sea branch arrives in Mumbai about ten days later, on June 10th. This is a fairly speedy progression.
• The Bay of Bengal branch moves quickly as well, arriving in Assam in the first week of June. Because of the high mountains, the monsoon winds deflect westward over the Ganga plains.
• The Arabian Sea branch of the monsoon arrives over Saurashtra-Kuchchh and the central part of the country by mid-June. The monsoon branches of the Arabian Sea and the Bay of Bengal join over the northwestern part of the Ganga plains.
• By the end of June (the tentative date is the 29th of June), Delhi usually receives monsoon rains from the Bay of Bengal branch. The monsoon arrives in western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan by the first week of July. The monsoon arrives in Himachal Pradesh and the rest of the country by mid-July.
• The monsoon's withdrawal, or retreat, is a more slow process. By early September, the monsoon has begun to recede in northwestern states of India. It completely retreats from the northern half of the peninsula by mid-October. The withdrawal from the southern half of the peninsula is relatively quick. The monsoon had left the rest of the country by early December.
• From the last week of April to the first week of May, the islands experience the first monsoon showers, which move progressively from south to north. From the first week of December to the first week of January, the withdrawal occurs progressively from north to south. The rest of the country has already been affected by the winter monsoon.