South-west monsoon exits

India Meteorological Department (IMD) has declared on Thursday that the southwest monsoon has withdrawn from the country. RAIN WATCH Southwesterly winds have been replaced by northeasterly winds over the south peninsula. Lowlevel northeasterlies that bring the northeast monsoon have been prevailing over the south peninsula over the past three to four days. The IMD has also mounted a watch for an increase in rainfall activity over extreme south peninsula from Sunday (October 25) that should presumably precipitate the northeast monsoon (reverse or winter monsoon). But, presently, the wind speeds are lacking in strength but the IMD has assessed that there are indications of development of a cyclonic circulation over southeast and adjoining southwest Bay of Bengal during the next two days. The circulation is expected to move west-northwest- wards. On Thursday, however, sea-surface temperatures (SSTs) were not favourable for `cyclogenesis' over the southeast Bay waters. But SSTs were clearly building over Bay waters towards the southeast coast, as per the US Navy Coupled Ocean Data Assimilation data. They were still higher just off the coast of Tamil Nadu on Thursday. The US Navy Operational Global Atmospheric Prediction System saw a cyclonic circulation wheeling in from southeast Bay of Bengal heading west into south west Bay of Bengal during October 22 to 28 and looking straight at the Tamil Nadu coast. The Fleet Numerical Meteorology and Oceanography Centre (FNMOC) of the US Navy saw organised showers approaching the Tamil Nadu coast around October 29 only. This is shown as happening in tandem with northeasterly winds picking in speeds of up to 20 knots and even beyond. The southern peninsula and adjoining northeast Sri Lanka are likely to benefit from these rains, the FNMOC said. WEAK `LOW' The European Centre for Medium-Range Weather Forecasts (ECMWF) saw a weak `low' sitting smack over central Bay of Bengal around Sunday even as Typhoon Lupit `looked the other way' to track northeast off the Philippines. Meanwhile, all leading models tracking the Madden-Julian Oscillation (MJO) wave with its alternating dry and wet phases saw negative outgoing long-wave radiation (OLR) values building over the peninsula and adjoining waters from October 25. Negative OLR values are a proxy for the presence of rain-bearing clouds, which can in turn be attributed to an incoming wet MJO phase. A wet MJO phase is known to trigger the monsoons, low-pressure areas and even cyclones. The Wheeler model says that the MJO wave will start tracking north from equatorial Indian Ocean to cover Sri Lanka and adjoining southern Indian peninsula, southwest Bay of Bengal and southeast Arabian Sea. This phase is likely to be `productive' and would stay as such until November 5. The Empirical Wave Propagation model employed by the US National Centres for Environmental Prediction concurs with this outlook and says that the MJO wave would be particularly active during October 31 to November 5 around Sri Lanka and adjoining southwest Bay of Bengal. The Jones model sees the strong MJO phase to last from November 7 to 11. STORM DEVELOPMENT These forecasts seem to jell with the prediction for storm development in the southwest Bay of Bengal during the first week of November by the Roundy-Albany model that tracks `cyclogenesis' around the globe. As per this model outlook, a causative `low' is seen as strengthening from around November 2 and would likely reach peak activity November 9. Meanwhile on Thursday, the minimum temperatures were below normal by 3 to 4 deg Celsius over many parts of central and east India. They were below normal by 2 to 3 deg Celsius over parts of northwest and interior peninsula. They were near normal over rest of the country. No significant change in minimum temperatures is likely during the next three to four days. Mainly dry weather is likely to prevail over most parts of the country during the next five days. Satellite pictures showed convective clouds over parts of south Bay of Bengal.