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  • Is it really very hot?

  • Thursday, 21st July 2016

Have you come across a Very Hot Weather Warning icon on the TV screen early in the morning with a temperature of just 28 degrees displayed next to it? How come such temperature is considered as "very hot"?

In fact, forecast is a main component of the Very Hot Weather Warning. Even if the temperature at the Observatory is only 27 or 28 degrees in the morning or the weather is relatively cloudy, forecasters may still issue or maintain the Very Hot Weather Warning when they forecast more sunshine leading to a significant rise in temperature. This is to remind the public to get well-prepared before they depart home, such as wearing suitable clothing, bringing sufficient drinks and sunscreen.

Figure 1

Sometimes the weather is very hot during the day with relevant warning in effect but the temperature at night only drops slightly (say 28 degrees or above, which is known as a "hot night"), the forecaster usually will not cancel the warning at night if very hot weather is forecast to recur the next day. This is to avoid confusion caused by the frequent changes in warning status.

The Hong Kong Observatory takes into consideration several factors when issuing the Very Hot Weather Warning. These include the atmospheric conditions, weather situations over different parts of Hong Kong, and the Hong Kong Heat Index which reflects the combined effect of temperature, humidity, wind speed and solar radiation. When the warning is in force, we should take appropriate actions to prevent heat strokes.

T.S. Tsoi & L.S. Lee

Last revision date: <15 Aug 2016>