La Nina pattern likely to disrupt global weather: WMO

World Meteorological Organization: A La Niña event could, more likely than not, develop in the second half of 2007. The last WMO El Niño/La Niña Update in March 2007 also noted an enhanced likelihood of La Niña development, and conditions were moving quite rapidly in that direction until a reversal occurred during May and early June. There remains considerable uncertainty over the timing and magnitude of further cooling in the central and eastern Equatorial Pacific, and indeed there is a possibility that basin-wide conditions, despite some cooling, will on balance remain neutral through the remainder of 2007. Development of El Niño during the period is considered very unlikely….

• In general, neutral or weak La Niña conditions have prevailed in the tropical Pacific during the first half of 2007;
• Movement toward a typical La Niña condition has been very unsteady during the March-June period. A strong break in the pathway toward La Niña occurred during May and early June, increasing uncertainty over whether a La Niña event would develop in 2007;
• Nonetheless, cool waters continue to be found beneath the central Equatorial Pacific, and forecast models continue to predict at least some surface cooling in the central and eastern Equatorial Pacific, with most dynamical models continuing to strongly favour La Niña development;
• While the fluctuating conditions in the Equatorial Pacific over the last few months tend to imply a possibility of neutral conditions continuing through the remainder of 2007, a La Niña event is considered, albeit slightly, more likely. Development of El Niño in 2007 is considered very unlikely;
• While it is possible that La Niña conditions may develop in the next 1 3 months, the timing and magnitude of such an event in 2007 continues to be uncertain, with no indications at this time of a particularly strong event in terms of sea-surface temperatures;
• In light of the above assessment, regions typically impacted by La Niña events are advised to take note of the continued enhanced risk of such an event this year…