Monsoon onset likely in next 3-4 days (as of 27-May-10)

Conditions are becoming favourable for the onset of southwest monsoon over Kerala during the next three to four days.
An India Meteorological Department (IMD) update on Thursday cited numerical weather predictions to project the formation of an upper air cyclonic circulation over southeast Arabian Sea during the next two to three days.
Meanwhile, a leading US-based forecaster has said that the present MJO (Madden-Julian Oscillation wave) signature does not favour full monsoon onset over India until at least a few days after June 10.
System strength
An MJO wave travels periodically from west to east in the higher atmosphere and has alternating ‘dry' (suppressed rain) and ‘wet' (rainy weather) phases. It has a major influence on ground weather, especially during monsoon.
While an upper air system is a good augury for the onset of the seasonal rains along the Kerala coast, there are apprehensions that the system descend to the lower levels and start strengthening.
The European Centre for Medium-Range Weather Forecasts (ECMWF) had indicated on Wednesday that the system may attain cyclonic strength early next month. The formation of a cyclone during the onset period is bad enough thanks to its capacity to rally entire moisture around itself and leave hardly anything for the mainland.
What is worse is the model prediction suggesting a north-northwest track to the system and away from the Kerala coast. A few models, though, suggested a calibrated eastward movement to the Kerala/Karnataka coast.
A majority of the models seemed to suggest that the system could be declared a cyclone by June 2 over east-central Arabian Sea. In a track reminiscent of the Super Cyclone Gonu of year 2007, this system might track further north-northwest and make an eventual landfall over Oman/Gulf of Eden.

WARMEST POOL
What will apparently propel the system is the presence of a very warm (31 to 32 degree Celsius) pool of seawater lying north-northwest from east-central Arabian Sea towards the Oman coast.
While the ECMWF has retained its outlook, a few others also have kept a watch for a possible system formation on Thursday.
Among them are the Global Forecasting System (GFS) of the Fleet Numerical Meteorology and Oceanography Centre, the Canadian Meteorological Centre and the Global Forecasting System (GFS) model of the US National Centres for Environmental Prediction (NCEP).
According to the Tropical Extended Area Prediction System of the Australian Bureau of Meteorology, winds around the southeast Arabian Sea represented a smorgasbord of southwesterly, westerly and northwesterly flows. This area of unsettled weather would now see increasingly organised convergence accompanied by convection prior to formation of the upper air cyclonic circulation.


The US-based forecaster was of the view that the present MJO phase does not favour full monsoon onset over India until at least a few days after June 10.
The southwest coast had wasted a golden opportunity during the last active phase of the MJO wave when the southwesterly flows precipitated the onset over Sri Lanka. The ‘miss' was occasioned by the spinning up of cyclone ‘Laila' in the Bay of Bengal that mopped up available moisture feed and rained it over Andhra Pradesh and Orissa.
The next active phase of the MJO wave would not set in before June 10, which would also coincide with the blow-over of the projected cyclone in the Arabian Sea.
According to the US-based forecaster, equatorial Indian Ocean basin is presently in the suppressed phase of the MJO whereas Southeast Asia, the Bay of Bengal, and parts of the West Pacific are presently in the active phase.
Suppressed MJO convection is likely to progress northward across India into early June, with the next active phase developing over the equatorial Indian Ocean not before June 10.
Such a pattern would not likely result in enhanced rainfall averaged over India until after June 15. The subsequent couple of weeks could be quite wet over the monsoon region, according to him.
The outgoing long-wave radiation projections, a proxy for the presence of clouds, also suggest that the heaviest rainfall at that time would favour eastern India and the Bay of Bengal.