El Nino may suppress monsoon

The developing El Nino, that refers to anomalous warming of the equatorial east Pacific, may work to suppress the Indian monsoon, according to a leading US forecast specialist.

"Our models do indicate that, says Dr Tony Barnston, Head-Forecasting at the International Research Institute (IRI) for Climate and Society at Columbia University. Viewed from this standpoint, mid-July warming trends in the tropical Pacific could decide the fate of the Indian monsoon one way or the other.

Writing to Business Line, Dr Barnston said that the El Nino does not appear to be very strong, but rather weak to moderate. It does seem likely that it will continue to develop, however.

"The heat content beneath the surface in the tropical Pacific, while above average, is not outstandingly high. I am saying that I doubt the El Nino will grow rapidly during the coming one month. I suppose the monsoon forecast update to be issued by India at the end of June will indicate at least a slightly more pessimistic all-India monsoon outlook than the one from nearly a month ago, Dr Barnston said.

A passing Madden-Julian Oscillation (MJO) wave (west-to-east travelling, big weather maker in the upper levels) may have had some role in bringing the recent westerly low-level zonal wind anomalies to the western tropical Pacific. These westerly wind anomalies helped kick-start the currently borderline El Nino.

SUB-SURFACE FUEL

If so, the El Nino may not strengthen quickly over the coming few weeks since the MJO moves on and does its own thing. It is the sub-surface warmer-than-normal water volume that is providing the fuel for the event to develop further.

If the summer unfolds before the El Nino develops significantly, then India may not suffer a very bad monsoon because of the El Nino. But if the Nino3.4 (central Pacific) and Nino4 (western Pacific) regions reach anomaly levels of 1 deg Celsius and 0.6 deg Celsius, respectively, by mid-July, this could make for a more clearly deficient monsoon.

"I wish we could be surer about the path of this developing El Nino. Rather than thinking it may fizzle, or that it may become a very strong event, we see it currently as becoming a weak, a weak/moderate, or a moderate event.

"We also don't know the likely speed of development. It could stall for a few weeks at the borderline, or strengthen to a weak/moderate level (+1 deg Celsius in central Pacific) by the end of July.

IOD OUTLOOK

The Indian Ocean Dipole (IOD, mimicking 'El Nino' to within the confines of the Indian Ocean basin), another major monsoon determinant, is currently positive, and may remain that way throughout the summer.

But the IOD will probably not receive any kick from the El Nino until September, Dr Barnston said. El Nino does tend to favour initiation of a positive IOD event, which is monsoon-aiding.

It is in September that the Indian Ocean SST anomaly near Indonesia/Maritime continent tends to become negative, and that in the western Indian Ocean tends to become positive.

Before September, it could weaken slowly over the coming two months, but it is impossible to predict just how it will behave, Dr Barnston said.

MONSOON ADVANCES

Meanwhile, after a two-week-long hiatus, the western flank of the monsoon current advanced to cover more parts of central Arabian Sea, Maharashtra, Karnataka and Andhra Pradesh on Sunday.

The northern limit passed through Alibagh, Pune, Solapur, Hyderabad, Kalingapattinam, Paradip, Bankura and Gangtok. The eastern end had not advanced correspondingly, thanks to nil activity in the Bay of Bengal.

India Meteorological Department (IMD) said that conditions are favourable for further monsoon advance over more parts of Maharashtra including Mumbai, remaining parts of Karnataka and Andhra Pradesh during the next three days.

The monsoon arrival in Mumbai will now be the most delayed since 1999. The two recent years when it made delayed onsets were 2007 (on June 18) and 2005 (June 19). But this was as late as June 25 in 1905 and 1959.