Thiruvananthapuram, Jan. 22
THE International Research Institute for Climate and Society (IRI) at Columbia University has assessed chances of a La Nina event occurring during January-March this year at 50 per cent.
The National Oceanic and Atmospheric Administration (NOAA) also confirmed that La Nina conditions have been developing, although the trend was `weak' for now.
La Nina is a condition characterised by cooler than normal sea surface temperatures (SSTs) across much of the equatorial and central Pacific, and is the reverse of El Nino. La Nina has been known to generate higher than average precipitation in Australia, India and Indonesia.
Strength of prevailing trade winds (east to northeasterly in the northern hemisphere and east to southeasterly in the southern hemisphere) is an indicator to evolving conditions over the equatorial central Pacific. The NOAA said persistent stronger-than-average low-level equatorial easterly winds have been observed over the central Pacific (aiding La Nina). Weak `trades' are generally associated with an El Nino.
La Nina events recur approximately every three to five years. The last one occurred in 2000-2001 and was a weak event.
Latest update from the IRI said cooler than average sea surface temperatures continue to develop in the eastern and central equatorial Pacific. Based on the latest observations and forecasts, the probability of a La Nina event over the January-February-March 2006 season is 50 per cent, it concluded.
During December 2005, sea surface temperatures (SSTs) have been approximately 1.0 deg C below average in the eastern Pacific and approximately 0.5 deg C above average in the western Pacific. The extent and magnitude of the colder than average conditions in the eastern Pacific have been increasing since mid-November.
There are now sufficient changes in the upper ocean thermal structure to maintain the cool SST conditions at least through the next several months. If the current conditions were to persist through March, a La Nina event would be officially acknowledged.
Prior to the 1980s and 1990s, strong El Nino events occurred on average every 10 to 20 years. In the early 1980s, the first of a series of strong events developed.
The El Nino of 1982-83 brought extreme warming to the equatorial Pacific. Surface sea temperatures in some regions of the Pacific Ocean went up to six deg C above normal.
It also had a pronounced influence on weather in the equatorial Pacific region and worldwide. Severe droughts occurred in Australia, Indonesia, India and southern Africa. Heavy rains were experienced in California, Ecuador, and the Gulf of Mexico.
Meanwhile, back home, a forecast by the National centre for Medium Range Weather Forecasting (NCMRWF) said a fresh western disturbance is likely to approach Jammu and Kashmir and will start affecting northwest India during the next two to three days.