'On Christmas Day, it is work as usual for those who are on duty, but because there is generally no adverse weather, the forecasters can work in a more relaxed atmosphere,' Mr Lam says. For the chosen few who have to work, they will spend a lot of the day answering media inquiries, especially if the day is warmer or colder than usual.

If you have always dreamed of a white Christmas, you'll probably have to keep on dreaming as it is unlikely that Hong Kong will wake up to an archetypal winter wonderland scene. 'The chances of a white Christmas are very slim,' Mr Lam says. 'Our records since 1956 shows that there were three cases of snow in Hong Kong [February and December 1967, and January 1971]. For nearly 40 years, no more reports of snow have been registered.'

Hong Kong has been engulfed in a generally warming trend, which has reduced the chance of snow even further. 'However, if one considers frost at Christmas as 'white Christmas', then it is quite possible,' Mr Lam says. 'In fact, frost or glaze ice have been reported for the past five years in a row.'

The average maximum temperature on Christmas Day is 19.4 degrees Celsius, and the average minimum temperature is 14.7degrees. The highest temperature recorded on Christmas Day was 25.8degrees and the coldest was 7degrees.

Mr Lam remembers particularly well the Christmas of 2005. 'Hong Kong was in the grip of an extremely long, cold spell and it truly felt like Christmas. But the most extensive frost in history in Hong Kong probably occurred in 1893, when the mercury registered 32 degrees Fahrenheit [0 degrees].'

Mr Lam's fascination with the weather began when he was young, and his curiosity grew as he got older. 'I started watching stars as a boy scout in Form Two and became very interested in astronomy. I also liked to follow the movement of typhoons, making use of the latitude and longitude readings broadcast by the Hong Kong Observatory over the radio. I even hoisted my own signals at home. This led me to study physics and then meteorology at university, which eventually took me to the observatory.'

After an eventful year at the observatory, Mr Lam is looking forward to relaxing this holiday season. 'I wouldn't say that this has been a bad year [weather wise], but it has definitely been an extraordinary year. We had the coldest February for the past 42 years, the most number of No8 tropical cyclone warnings since 1999, and the wettest June ever [since records began in 1884]. It's been one of the most hectic years for our forecasters.'

Responding to the recent praise that the observatory has received for accurate forecasting and timely hoisting of typhoon signals, Mr Lam says: 'We are pleased that people recognise our effort to deliver an efficient warning service. It does worry us sometimes that our warnings trigger off so much action with significant impact on people's life. But we also treat it as an honour to be useful to the community. It is not without stress that we perform our function. But we have to learn to live with it, and to see the positive.'

Staff will celebrate the season with their annual party on the last working day before Christmas. All present and retired colleagues and their families attend, and awards are handed to staff who have excelled throughout the year.