The extremely powerful Typhoon Ragasa, the 18th typhoon of the year, is heading for Guangdong Province and could prompt a red alert — the highest warning level — in Shenzhen as early as tomorrow, the Shenzhen Meteorological Observatory warned yesterday. A white alert was issued at 6 p.m. yesterday. Forecasters say landfall is most likely to occur along the central-to-western Guangdong coast between the pre-dawn and afternoon hours of Wednesday