e. Indian summer monsoon

The Indian summer monsoon typically lasts from June-September (Fig. 58d), with large areas of western and central India receiving more than 90% of their total annual precipitation during the period, and southern and northwestern India receiving 50%-75% of their total annual rainfall. Overall, monthly totals average 200-300 mm over the country as a whole, with the largest values observed during the heart of the monsoon season in July and August.

There was an early start to monsoon conditions during 1996, with monsoonal rains completely covering India by 30 June, 2 weeks earlier than normal. There was also a late finish to the monsoon season, with a complete withdrawal of monsoonal rains from India not seen until 11 October. For the area as a whole, rainfall was above normal during June and July, near normal during August, slightly below normal during September, and then substantially above normal during October (Fig. 58d). In fact, average October totals nearly equalled those observed during September.

Regionally, the 1996 monsoon season brought near-normal rains to large portions of central India (Fig. 58b). Above-normal rains were observed over the southern, coastal western, and north-central regions, while significantly below-normal rainfall (deficits exceeding 1500 mm and totals falling below the 10th percentile) was confined to the east-central region, including much of Burma and Bangladesh (Fig. 58c). Normally, the heaviest monsoonal rains are observed in these regions.

In contrast, the largest rainfall totals of the season were observed in southwestern coastal India, where more than 1200 mm was reported at most locations (Fig. 58a) and a seasonal high of 2760 mm was reported in Mangalore (located in coastal Karnataka). These totals averaged 200-300 mm above normal (Fig. 58b), but were below the 70th percentile based on the 1961-90 base period means (Fig. 58c). In southeastern India, large totals of 600-800 mm (200-300 mm above normal) during the season primarily resulted from a rare tropical cyclone on 14-17 June, which moved westward into the region from the Bay of Bengal. This storm brought 350 mm of rain in 24 hr to Chennai on 14 June, which is a record single-day total for the month of June. Kioda, in Telangana, reported 670 mm of rain on 17 June, which is also an all-time record. A second tropical storm to affect India formed over the Arabian Sea and crossed northwestern India on 19 June. This system contributed substantially to the abnormally large seasonal totals (800-1000 mm) observed across the region (Fig. 58a).

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