Saturday, March 20, 2010

Better model convergence on normal monsoon outlook

The latest update from the International Research Institute (IRI) for Climate and Society at Columbia University has retained the outlook of maximum probability for a normal monsoon for India this year.

The IRI also suggested that the season might end in a flourish during July-August-September with odds favouring surplus rain for west-central India and parts of north-west and east-coastal India.


This is a pattern identified with a favourable (positive) phase of the Indian Ocean Dipole (IOD), a miniature El Nino-La Nina combo enacted in the Indian Ocean.

The west Indian Ocean warms relative to the east during a positive IOD phase and vice-versa in a negative IOD.

A positive IOD is considered as supportive of a concurrent Indian monsoon. Dr Jing-Jia Luo and his team at the Research Institute for Global Change (RIGC) in Tokyo had earlier informed Business Line that it was possible that a weak positive IOD might be there for the asking towards September.

The RIGC had also observed that the current El Nino phase would fade out over the next few months to be followed by a possible La Nina.

A positive IOD and weak El Nino transitioning to La Nina are good signals for the Indian monsoon.


A major highlight from the IRI forecast update was least probability of an otherwise usual but deadly heat wave stalking the east coast (Orissa and Andhra Pradesh) in the run-up to the monsoon.

Extended, though abstract, forecasts by the US National Centres for Environmental Prediction (NCEP) from April-May-June to September-October-November too support the case for a largely normal monsoon for the country this year.

But, the NCEP has pointed to a persistent weather anomaly on the eastern coast of the country around Orissa and Gangetic West Bengal where rains are likely to be in deficit all through the season.

The European Centre for Medium-Range Weather Forecasts (ECMWF), which is expected to come out with a latest seasonal forecast update within the next few days, has, till now, suggested maximum probabilities for a normal monsoon.


The ECMWF has been more liberal in its outlook with monthly disaggregated rainfall surpluses at varying places falling within the monsoon print.

No model has yet indicated the possibility of a repeat of the severe rain deficit for northwest India.

Meanwhile, on Friday, a daily IMD update said that heat wave to severe heat wave conditions prevailed over many parts of Gujarat and isolated pockets of south-west Rajasthan and West Madhya Pradesh.

Maximum temperatures were above normal by 4 to 6 deg Celsius over Rajasthan, the western Himalayas, Punjab, Haryana, Madhya Pradesh, Chhattisgarh and the north-eastern States. The highest maximum of 43.0 deg Celsius was recorded at Deesa in Gujarat.


A further rise in maximum temperatures has been indicated over parts of northwest, west, central and east India during the next three days.

A warning issued by the IMD said that heat wave conditions would continue to prevail over parts of Gujarat and south Rajasthan during the next two days.

They may even extend into some parts of Madhya Pradesh, Chhattisgarh, Vidarbha, Telangana and interior Orissa thereafter. Generally clear skies and dry air are prevailing over northwest and central India ahead of the expected arrival of a fresh western disturbance over the western Himalayas.


The IMD has forecast scattered rain or snow over Jammu and Kashmir from Sunday. Isolated rain or thundershowers are also likely over parts of the north-eastern States the same day before increasing thereafter. Isolated rain or thundershower has been forecast over Orissa during the next 24 hours.

An outlook until Wednesday suggested that scattered rain or snow would occur over Jammu and Kashmir while being isolated over Himachal Pradesh.

Scattered rain to thundershowers accompanied with isolated thunder squalls is likely over the north-eastern States during this phase.
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