Arrival and withdrawal dates of the summer monsoon in Bangladesh

Abstract

AbstractDaily data of (a) rainfall amount, (b) prevailing wind direction, (c) wind speed, (d) mean temperature, and (e) mean relative humidity of 19 stations in Bangladesh for the months May through to October, for the period 1958 through to 1987, have been analysed in order to determine various spatio‐temporal patterns of the arrival and withdrawal dates of the summer monsoon in the country. Statistical characteristics of these dates have been presented.The summer monsoon arrives first in the extreme south‐eastern part of the country, and initially moves towards the north. After being diverted by the Meghalaya Plateau, the flow turns towards the west. The mean arrival date of the summer monsoon in the extreme south‐eastern coastal part and in the extreme north‐western part are 2 June and 15 June, respectively. Withdrawal of the summer monsoon proceeds in the opposite direction to the arrival. Mean withdrawal dates of the summer monsoon from the extreme north‐western part and extreme south‐eastern part of the country are 30 September and 17 October, respectively. Standard deviations of both arrival and withdrawal dates in different parts of the country vary from 7 to 10 days.Probabilistic early dates of arrival of the summer monsoon in Cox's Bazar area in 1 year out of 4 years, 10 years, and 25 years are 28 May, 23 May, and 19 May, respectively. Probabilistic late dates of arrival in 1 year out of 4 years, 10 years, and 25 years are 8 June, 13 June, and 16 June, respectively.Probabilistic early dates of complete withdrawal of the summer monsoon from Bangladesh in 1 year out of 4 years, 10 years, and 25 years are 10 October, 5 October, and 1 October, respectively. Probabilistic late dates of complete withdrawal in 1 year out of 4 years, 10 years, and 25 years are 23 October, 28 October, and November 1, respectively.