20-Occurence of heavy rain episodes over Madras.

Abstract

Heavy rain episodes over a place paralyses life and activities, especially in the metropolitan cities. Hence the detailed informations on heavy rain episodes over a location will be of immense help to various agencies. The heavy rain episodes (24 hourly rainfall 7 cm) during 1967-86 (77 in number) over Madras (Meenambakkam) have been examined and the results are presented. While 78% of heavy rain episodes occur during the Northeast Monsoon months of October to Decemher, the month of March, April and June are free from heavy rain episodes. Only in less than half the number of occasions (400 the heavy rain occurrences are associated with clearcut synoptic systems like depressions and cyclones. Episodes of heavy rain greater than 15 env!. form only 16%" of total heavy rain occasions. Late night appears to be the preferred period of high intensity rainfall in about 26% of occasions. The chance of northeast monsoon rainfall being normal or above normal is 400d when at least four episodes of heavy rain occur over Madras during this period. The duration, number spells and association Ath rainfall activity over rest Tamilnadu have also been discussed.