Temperatures will tumble to about 20 degrees Celsius on Sunday as a northerly airstream hits the city with strong winds. Although sunny periods and temperatures of up to 29 degrees are expected today, the weekend will be cooler, windier and cloudier. 'A northerly airstream from southern China will arrive [tomorrow], bringing cooler weather,' Observatory scientific officer Tong Yu-fai said. The temperature will fall to between 23 and 26 degrees tomorrow, and 20 to 25 on Sunday. The weather will then deteriorate, Mr Tong said, with Severe Tropical Storm Chanchu, which will cross the Philippines in the coming days, bringing rain and wind between Monday and Wednesday and possible heavy rain and squalls on Thursday.