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Friday, 13th June 2014

Take Precautions against the Heat

You may have noticed that the Observatory recently issued Special Weather Tips on hot days to remind members of the public to take precautions against the heat. This is a new service launched by the Observatory this summer - the "Hot Weather Special Advisory". It aims to raise public awareness of taking appropriate precautions when the weather is rather hot but not to the extent that warrants the issuance of Very Hot Weather Warning. In fact, according to press reports from 2005 to 2013, the average number of people suffering from heat-related illnesses was about 75 per year, out of which around 4 people died per year. Indeed, it is crucial to be alert of the impact of hot weather to health. Details of the Observatory's new service and the precautions against hot weather can be found via the following link:

When issuing the "Hot Weather Special Advisory" or the Very Hot Weather Warning, the Observatory considers basically the same factors but with different degrees. It is not a must for a "Hot Weather Special Advisory" to be followed by a Very Hot Weather Warning; it depends on whether the weather will become hotter. The concerned factors include the atmospheric environment, the weather conditions at different places in Hong Kong, and the trial Hong Kong Heat Index. The index represents the combined effect of temperature, humidity, wind speed and solar radiation; and is calculated from the natural wet bulb temperature, the globe temperature and the dry bulb temperature measured at King's Park Meteorological Station. Real-time Hong Kong Heat Index can be found in the Observatory's webpage:

Figure 1

Figure 1      Observatory's website displaying real-time Hong Kong Heat Index.

Up to this point, you may recall that the Observatory once made reference to the Wet Bulb Globe Temperature (WBGT) when providing services for the 2008 Olympic Equestrian Events. The calculations of WBGT and the Hong Kong Heat Index are indeed based on similar parameters. The former was developed based on the climate of western countries, while the latter was developed by taking into account the relationship between local hospitalization rate and meteorological observations. This new index was a concerted effort of the Observatory and local university, in consultation with different stakeholders. It was more applicable to the environment of Hong Kong, which is characterized by the generally higher humidity.

Since the measurement of hot weather at King's Park is closer to the average value over different regions in Hong Kong, and that the Hong Kong Heat Index was developed by using data from King's Park and the territory-wide hospitalization counts, the index could represent the overall condition in Hong Kong. Generally speaking, when the forecast index is about to reach 30, the Observatory will consider issuing the "Hot Weather Special Advisory" after taking into account a range of other factors. If the index is forecast to be even higher, the issuance of Very Hot Weather Warning will be considered. The Hong Kong Heat Index is currently used on a trial basis. Since there is only limited research data, further categorization of the index cannot be made at this moment. The Observatory will continue to collect more data for evaluation and research with a view to further enhancing the hot weather service in the future.

LS Lee and KL Lee

Last revision date: <01 Dec 2014>