None of the low pressure systems this monsoon developed into depression
The just concluded southwest monsoon was unusual in one respect — none of low pressure systems that took shape during the four-month season went on to intensify into a depression.
India Meteorological Department (IMD), in a report on Saturday, said 10 low pressure systems had taken shape over the Indian subcontinent during the season from June to September. Four to six of such systems usually intensify into depressions, bringing vigorous spells of rain and driving the rain-belt inland from the coasts.
However, this was the first time since 1981 when the season saw no low pressure system at all forming in June. The season started on a very lethargic note. Of the 10 systems of the season, two came in July, five in August, and three in September.
Rainfall for the country as a whole was only 92 per cent of the long period average, with June bringing only 72 per cent of its usual quota of rain, July 87 per cent, August 101 per cent and September 111 per cent. The situation at the half-way mark had seemed hopeless, but the months of August and September salvaged the season to some extent.
In fact, the monsoon, since its onset over Kerala on June 5, had been so weak this time that it was not until July 7 that the first low pressure system of the season evolved. Its position was over northeast Madhya Pradesh and adjoining south Uttar Pradesh. A system born far inland usually would not have much steam, but this one helped the monsoon to cover the whole country by July 11, though without much energy.
Another noteworthy change from the usual pattern was that none of the 10 low pressure systems was on the Arabian Sea side of the subcontinent.
When a good monsoon falls into its groove, it will be driven by a sort of twin-engine — one being a low pressure system on the Arabian Sea side and the other, a system on the Bay of Bengal side of the subcontinent. One of the two engines just did not work this time.
The report notes that there had been extended periods of subdued rainfall activity during the season in different spatial scales, but something of an “unorganised convective activity”, which is characteristic of weak monsoons, contributed significantly to the seasonal rainfall.