During the second half of the period under consideration tem perature rises, and in April the greater part of the country has an actual mean of over 80°F. India becomes relatively a low-pressure area, so that the north-east monsoon blowing over the ocean is weakened, and winds blow inland from the Bay of Bengal and the Arabian Sea. As these winds are saturated with moisture, considerable precipitation takes place, chiefly in Malabar, Tenasserim, Bengal, and Assam.
When the low-pressure area over Northern India and adjacent lands closes up with the equatorial low-pressure belt during the summer months, the atmospheric conditions are entirely changed. The north-east monsoon disappears and its place is taken by the south-east trades, which are sucked across the equator and reach India as the south-west monsoon. This is heavily charged with moisture and brings to the country about 90 per cent. of its total rainfall. One branch of the current strikes the Western Ghats upon which it deposits much rain ; it then crosses the Deccan, to which, however, it only brings occasional showers ; and finally it unites with the other branch of the monsoon current which has advanced up the Bay of Bengal. This latter branch is directed
in the first instance towards Burma and Tenasserim, but part of it is deflected, first by the Arakan Hills, and later by the Himalayas, so that it passes in a north-westerly direction up the basin of the Ganges, and into that of the Indus. Here it is joined by the northern part of the Arabian Sea current which, on account of the low elevation and great heat of the land, has passed over western Rajputana without depositing much moisture except in the neighbourhood of the Araval1i range.
June, and more particularly July and August, are the months of heaviest rainfall. In September the monsoon begins to withdraw southward, as the low-pressure area over the land is gradually filled up, and a shallow depression over the Bay alone remains. This depression, which gradually moves southward, sucks in the south-westerly winds so that they blow on to the east coast of peninsular India, where they deposit considerable moisture. By the middle of December this depression has passed out of the Bay, and the conditions of the north-east monsoon again prevail over the whole Indian area.