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Thai mahouts ride their elephants through the flooded Ayutthaya streets on October 10, 2011. |
Wed October 12, 2011
By David Challenger, CNN
(CNN) -- Is this just a normal year, or is the southwest monsoon acting more aggressively than normal?
The 2011 tropical cyclone season in the west Pacific has been about average, not significantly above or below usual events. We did have a few consecutive storms that made landfall in the Philippines and other parts of South East Asia in late September and early October, such as Haitang, Nesat, and Nalgae -- but that had more to do with a steering pattern caused by high pressure over the Pacific, not the monsoon. The remnants of these storms did make their way farther into South East Asia, which likely enhanced the monsoon trough, thus leading to higher than average rainfall in countries such as Thailand, Cambodia, Laos and Vietnam. Rainfall in most of Thailand is running 15% to 25% above average for the year (with a vast majority of that rain coming in the monsoon months of May to October).
What exactly is the southwest monsoon? When does it start, end, and how is it generated?
The southwest monsoon occurs during the northern hemisphere summer, and is caused by the land masses of the Indian subcontinent and South East Asia heating up faster than the Indian Ocean. This creates an influx of cooler, moisture-laden air from the ocean over the land. The southwest monsoon generally begins in mid-May and ends in late October/early November, though start and end times vary based on location. India, for example, has a southwest monsoon season that begins June 1 and ends September 30.