A former Hong Kong Observatory chief has slammed the government’s heat stress warning system for issuing only the lowest alert during Sunday’s record-breaking heat. Temperatures reached the highest level of record on Sunday as a heatwave influenced by Tropical Cyclone Dolphin continued to affect Hong Kong. Heat index ‘unsuitable’Lam said that the Hong Kong Heat Index underestimates the heat stress effects of direct solar radiation, especially for outdoor workers. “The solar radiation weighting within the Hong Kong Heat Index is very low, making it unsuitable for outdoor work environments,” he said. The department added it will monitor the weather and the heat stress warning to determine if there is any need for optimisation.