The monsoon has entered the North-East on Wednesday with a delay of almost five days, while covering the remaining parts of Tamil Nadu. The seasonal rains checked into Mizoram, Manipur, Tripura and parts of Assam and Nagaland, as a prevailing low-pressure area over the Bay of Bengal buzzed in the background.

The India Meteorological Department (IMD) said that northern limit of the monsoon passed through Karwar, Shivamogga, Tumakuru, Chittoor and Ponneri and across the Bay of Bengal into Agartala and Kohima. The low is expected to mover West-North-West towards the Odisha coast and intensify over the next two days.

Located over East-Central and adjoining West-Central Bay on Wednesday, the low has brought in very intense cloud-building activity principally over the Central Bay and the Andaman Sea. Odisha, North Coastal Andhra Pradesh and Telangana are in for heavy rains on both Wednesday and Thursday.

Heavy rain forecast

Heavy rain is forecast on Wednesday over Telangana, Rayalaseema, Chhattisgarh, Assam, Meghalaya and the North-Eastern States. Thursday will bring heavy to very heavy rainfall with extremely heavy falls over Coastal Andhra Pradesh; heavy to very heavy rainfall at isolated places over Rayalaseema, Telangana and Odisha.

It would be heavy over Kerala, Lakshadweep, Coastal Karnataka, Konkan, Goa, Madhya Maharashtra, Vidarbha, Chhattisgarh, hills of West Bengal, Sikkim, Assam, Meghalaya and the rest of the North-Eastern States. On Thursday, high winds (40-50 km/hr) may prevail along and off the North Tamil Nadu-Andhra Pradesh-Odisha Coasts. Fishermen are advised not to venture into these seas.

Meanwhile, the Application Laboratory of the Japanese national forecaster Jamstec has said that weak La Nina (a friendly climate event for the Indian monsoon) conditions are currently developing in the Equatorial East Pacific. Its SINTEX-F predicts that this condition may persist into the latter half of this year.

But the Australian Bureau of Meteorology (BoM) quoted global models suggesting further cooling but neutral (neither El Nino/La Nia) conditions prevailing during June-August. Two models out of eight see La Nina thresholds being exceeded in September-November, while two others bet on just thresholds, it added.

The BoM added a caveat saying that predictions on Pacific conditions made during this time of the year have lower skill than those made later in the year. If further cooling is observed in coming weeks, and any additional models suggest La Nina development, the BoM would declare an official La Nina watch.

Uncertain La Nina-IOD outlook

The BoM said that models show a broad spread of likely scenarios between the neutral and negative Indian Ocean Dipole (IOD), a see-sawing of ocean temperatures in the basin closer home as in the Pacific. A record positive IOD (warmest in the western basin) had powered a surplus monsoon last year.

Unlike earlier predictions, most model updated have shown a lower likelihood of a negative IOD (warmth shifting to East Indian Ocean). However, the Japanese agency begs to differ here saying that observations show that the western basin of the Indian Ocean basin is currently warmer-than-normal.

The Japanese agency predicts a moderately positive IOD during summer that quickly decays into the autumn — ironically the period when a typical IOD condition usually matures. As in the case of the BoM, it also pointed to large uncertainty in outlook with 15 per cent of the ensemble members predicting a negative IOD.

In this contest, the IMD had said in its second long-range monsoon forecast update earlier this month that neutral conditions exist both in the tropical Pacific and Indian Ocean. The IMD expected the cooling Pacific to enter a weak La Nina phase while the Indian Ocean might slip into negative IOD phase.

Still, the IMD had upgraded its overall monsoon outlook (quantum of rainfall within the normal range of 96-104 per cent) from 100 per cent in April forecast to 102 per cent. All three of the four geographic regions of the country are expected to receive 100 per cent or above rainfall, while it would be 96 per cent in the North-East.

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