Test which way the wind is blowing today. Is it coming at you from the southwest? Then the chances are the summer monsoon has started and perhaps you are also soaking wet or under an umbrella as it blows in the first of the summer rain. By rights the monsoon should have started yesterday, according to one group of meteorological researchers who have used 10 years of rainfall data to work out that May 10 is the average start date of the summer monsoon in Hong Kong. But another group has calculated it should start between May 16 and 20. Add to that the effects of the record 1997-98 El Nino, and reportedly slow melting of the Tibetan ice this year. Both are known to delay the monsoon, which therefore may not come until late May. That is not good news for hundreds of researchers in the region who have already started a 20-day intensive monitoring period for the world's first direct study of the monsoon. Professor Richard Johnson of the Department of Atmospheric Science at the University of Colorado and a co-investigator on the South China Sea Monsoon Experiment (SCSMEX) said at the Hong Kong University of Science and Technology last week that organising a huge effort such as this, with two research ships from China, two from Taiwan and one from Vietnam, meant timing had to be fixed in advance. The researchers began the monitoring on May 5 to study the pre-monsoon temperature, wind speed and humidity, and will stop on May 25, which they hope will give them data from after the start of the phenomenon. The twice-yearly Asian monsoon is one of the world's major weather patterns. In the summer, the changes in wind direction from easterly to southwesterly, which then bring the rain-laden air from the sea northward across China, are seen across the world, but are at their strongest in this region. It has never been clear where the Asian monsoon begins, but research models indicate it may start in the South China Sea before moving northward. The currents from the southwest carry the uppermost layers of water to the northern South China Sea and warm it by a couple of degrees, while the southern part cools as deeper water rises to replace it. But so far all this is theoretical. 'Now we want to test this with observations,' the professor says. This year sees the first attempt, with operations led from the meteorological office in Guangzhou and including major input from Japan and various US research organisations. Other sites throughout Asia are sending up four weather balloons a day - or as many as they can manage, since each one costs US$1,000 (HK$7,735). And two radars, one on China's Dongsha Island, will continue their work during the monsoon, he says. But Professor Johnson says the project has already achieved something - the putting aside of politics for the sake of science. Not only are Taiwan, Vietnam and China all supplying ships, they are allowing them to sail into contested areas to take data.