The Hindu Business Line : 21% surplus rain in June, more seen coming

Thiruvananthapuram, July 3 The monsoon has delivered a surplus of 21 per cent during the first month according to the all-India area-weighted rainfall statistics valid as of July 2.

An India Meteorological Department (IMD) update said the number of Met sub-divisions receiving excess to normal rainfall was unchanged at 28 from last week, while the rain-deficit were fewer by two (eight from 10).

The surplus was concentrated to the north and northwest, while deficit was scattered over the interior peninsula, Kerala in the south, and Assam and Meghalaya in the east.

Marathwada (-56 per cent) topped the charts, followed (in percentage figures) by Rayalaseema (-38); north interior Karnataka (-34); Assam and Meghalaya (-30); Kerala (28); Gujarat and Madhya Maharashtra (-27); and coastal Andhra Pradesh (-24).

RENEWED MJO WAVE

But a renewed Madden-Julian Oscillation (MJO) wave of anomalous precipitation is forecast to traverse the warming West Indian Ocean from this weekend to trigger another productive wet spell over the west coast and possibly the peninsular interior.

The MJO travels in a west-to-east direction from Africa into equatorial Indian Ocean to the western Pacific and even beyond in stages. As it ambles towards mainland India, it breaks up into the Arabian Sea and the Bay of Bengal components.

The tenure over the territorial Indian waters and the landmass lasts up to a week or more depending on the wave amplitude and results in enhanced monsoon rainfall. Various models tracking the event have suggested that the wave would be active from Sunday.

Short-to-medium term forecasts by the European Centre for Medium-Range Weather Forecasts (ECMWF) too, endorsed this outlook by predicting renewed rain activity starting from northwest Bay, progressing into central India and peaking over the Konkan-Mumbai-south Gujarat belt during the next week.

WHEELER MODEL

The Wheeler model, which is considered among the most authentic, sees the wave establishing over east-central and adjoining east Arabian Sea around Sunday. It would progressively engulf almost the whole of the Arabian Sea and filter into interior west peninsula bordered on the north by Konkan by July 11.

The next five days would see the wave stretching into south Gujarat and over the entire peninsula, even sneaking its way into southwest Bay of Bengal. By July 21, the MJO wave will lift over south extreme peninsula, but will continue to be active over northeast Arabian Sea, interior west peninsula and the southwest Bay, including coastal Tamil Nadu. Going forward, the activity will weaken and die out by July 31 giving way to a regime of suppressed rain activity in the region.

The equally respected Jones MJO model too, painted almost a similar picture, while others contested only the dates from when the activity would become pronounced over the West Indian Ocean, which is the springboard of the positive Indian Ocean Dipole (IOD) event seen driving the monsoon this year.

WHIRL ACTIVE

Meanwhile, the IMD said in its update on Thursday that the offshore trough extending from the Gujarat coast to the Kerala coast with an embedded cyclonic circulation over northeast Arabian Sea persisted. Fairly widespread rainfall with isolated heavy to very heavy falls has been forecast for Konkan, Goa, Gujarat and Saurashtra for two more days.

In the east, the upper air cyclonic circulation has shifted base to over east Uttar Pradesh and neighbourhood.

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