The Hong Kong Observatory issued a 'very hot weather' warning for the second time in eight days yesterday - urging the public to protect themselves from the scorching sun. The mercury topped 33.3 degrees Celsius at Chek Lap Kok, 27.4 degrees at the Peak and 32.1 degrees at the Observatory in Kowloon yesterday. Temperatures are predicted to hit 33 degrees today. Yesterday's heat claimed some who felt unwell after joining the mass rally in the afternoon. The first very hot weather warning this year was issued on 24 June. The hot weather warning is issued if the observatory expects temperature to reach 33 degrees or above. Following the warning system's introduction in January 2000, the Observatory issued 12, 13 and seven very hot weather warnings in 2000, 2001 and 2002 respectively. Although such warnings are usually released at 4.30pm the previous day or 8am the same day, yesterday's was issued at 5.45am. 'Based on the information we had first thing this morning, we were able to issue the warning at the time we did,' said duty scientific officer Clarence Kung. He said the timing of the weather warning depended on how confident the Observatory was that it could predict likely weather outcomes. High temperatures can lead to heatstroke and sunburn, the Observatory said. It advised people to avoid prolonged exposure to intense sunlight. Loose clothing, suitable hats and UV-absorbing sunglasses could also reduce the chance of sunburn caused by solar ultraviolet radiation, it said.