Measuring individual droplets was part of his master's research project when he was still a physicist at the University of Hong Kong and that work was to lead to his present standing as one of the world's foremost experts on tropical cyclones and the science of climate change.
"I always wanted to study something to do with the weather," says Chan. He traces this interest back to his time as a Boy Scout, wondering why a day's hike often started in sunshine but ended in a downpour.
"That initial project was very simple. I built equipment to shine light through a hole across which raindrops fell," Chan says. "By counting the pulses and with the necessary calibration, the light blocked from the receiver on the other side could tell you the size of the drop and, therefore, how much water there was."
Correlating this information with distribution patterns and radar readings of local weather systems made it easier to assess total rainfall and drew Chan further into the study of atmospheric science and the physics of cloud formation.
Having collaborated with the then Royal Observatory during his master's, he knew there were limited options to research meteorology in Hong Kong. He headed first to the University of Hawaii in the mid-1970s to measure raindrops in clouds, and then to Colorado State University to take on a project with immediate practical purpose and - for a Hongkonger - obvious appeal.
"It was to study tropical cyclones - typhoons - and the physics that cause their movement," Chan says. "A typhoon is not a solid object like a cork floating in a river; it is not that simple. My PhD explained the different flows involved [depending on the position and direction]."
Returning in 1986 for a role at the Observatory, Chan admits to feeling slightly "lost" at an organisation whose focus was on improving operational forecasts rather than doing research into what causes the weather. He leapt at the chance to join the just established City Polytechnic (now CityU)
where he was later able to research phenomena of special int