Prominent southwest monsoon predictors are: the rainfall at earmarked 14 stations and the outgoing long wave radiations (OLR) over the stipulated window 5°-10°N and 70°-75°E. Prevalence of westerly winds with sufficient depth and speed remains a necessary condition over the equatorial belt over southeast Arabian Sea. All these parameters are displaying promising signs for, before time onset of monsoon.
Southwest monsoon arrived as early as 18th May in 2004 and as late as 18th June in 1972. In view of El Nino factor likely to remain neutral till mid 2004, a normal monsoon was forecast by most , including the National Weather Agency. However, El Nino developed early in the season with ONI (Oceanic Nino Index) ranging from 0.5°C and 0.7°C during Jul-Aug-Sep. Season as such ended with a drought with rainfall deficiency of 14%. Even 1972, the year of latest arrival of monsoon, concluded with a severe drought and holds record of being the most deficit with a shortfall of huge 24%. It only goes on to prove that, early or late arrival of monsoon is not to be linked with further prospects of seasonal rains.
Southwest monsoon arrived early by 1 week , on 16thMay, over Andaman Sea. It has covered more parts of Bay Of Bengal and has also reached Sri Lanka. Next stop , as predicted by Skymet, is likely to be mainland Kerala on around 26thMay. The advance of monsoon surge over the Island nation Sri Lanka is hastened by a well marked low pressure area over North Andaman Sea, in the proximity of Gulf of Martaban. The weather system may intensify further and make the monsoon arm of Bay of Bengal more powerful. However, this system is likely to move northeast and enter land within next 48hr.
Onset over Kerala will have to wait for yet another wave, for before time arrival on around 26thMay. Pre- Monsson activity has been widespread and vigorous too, over state of Kerala, more so for the northern half . Coastal Karnataka, including Mangalore was pounded by pre monsoon thundershowers repeatedly, over the last few days.
Although this weather activity is likely to reduce in magnitude and ferocity over the next few days, yet it remains good enough to meet onset criteria. Most stations over Kerala, Lakshadweep and Karnataka have far exceeded the markers of onset, on successive days between 16th-20th May. OLR values have also been locked well within the margin of onset standards. “ Countdown of impending onset starts on a promising note”.