The Hong Kong Observatory will issue the No 1 standby signal between 8pm and midnight on Monday as Tropical Cyclone Toraji is expected to enter within 800km (497 miles) of the city, and may consider raising the No 3 warning the next day.
The storm currently across Luzon in the Philippines is expected to move west-northwest at about 22km/h (14mph).
“Toraji will move towards the vicinity of the western coast of Guangdong to the Pearl River Estuary in the next couple of days,” the forecaster said.
“Under the combined effect of Toraji and the northeast monsoon, winds over the region will gradually strengthen with squally showers.”
The Observatory said it would consider issuing the No 3 signal between Tuesday and Wednesday.
It added the storm might be “relatively close” to the vicinity of the Pearl River Estuary by Thursday, but could also weaken during that time.