Current weather data indicate that there could be a short ‘break monsoon’ spell during the first week of August, according to P.V. Joseph, expert researcher and former director of Met Department.

This will decrease the rains over most of India but increase the activity in the Northeast and hopefully wipe off the existing large deficiency there, he told Business Line.

LULL IN ACTIVITY

‘Break monsoon’ refers to the lull in monsoon activity across the country except in the Northeast after it runs through its initial course.

On occasions in the past, the ‘break’ has prolonged, leading to moisture stress and resultant adverse implications for standing crops.

But, as Joseph hinted, the break is expected to be short this time, which is amply supported by the outlook from international forecasting agencies.

Giving an update, he said the long-period average date of monsoon onset over Kerala was June 1 (based on a hundred years of data).

The onset happened on June 1 this year, but the rains needed just two weeks to move to the northern parts of the country. This usually takes a month.

Thus, the second half of June delivered huge excess rains over the northern parts except the northeastern States, which had deficit rains.

There was no “break” in monsoon in June and July and it was a continuously active monsoon in 2013, Joseph said.

Explaining, he said that there is a feature of the monsoon called low level jetstream, a fast-flowing air current with high winds of 40 to 60 km/hr flowing at an altitude of 1.5 km.

This stream is a carrier of the moisture required for monsoon rains and it gives the large scale dynamics for monsoon rain production.

LOW-LEVEL STREAM

During an active monsoon, the stream flows through peninsular India with its axis close to the latitude of Goa.

Heavy rains occur north of the axis. Low-pressure systems and monsoon depressions form and move in this zone north of the axis. This was happening in the second half of June and the whole of July this year, a continuous active phase of the monsoon.

As on July 29, the rainfall that India got from June1 is 19 per cent in excess. During the same period, Kerala received 39 per cent excess rains.

In a ‘break’ monsoon, the low-level jetstream moves south and begins to flow south of Sri Lanka, shutting off the moisture supply to India and stopping the production of low-pressure systems.

It is during this phase that Assam and adjacent States get copious rains and the rest of India will have subdued rainfall, Joseph added.

Two factors adverse to monsoon rains in India are the El Nino warming of the East Pacific and excess tropical cyclone activity in the West Pacific Ocean.

So far, conditions in the East Pacific (actual and forecast) are El Nino-neutral and the West Pacific is forecast to have a normal season for cyclones.

In June and July, the West Pacific produced five named tropical cyclones (Yagi,Leepi, Bebinca, Rumbia, and Cimaron) and one typhoon, Soulik. This activity is just around the normal, Joseph said.

vinson.kurian@thehindu.co.in

(This article was published on July 30, 2013)
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