Penang Fire and Rescue Department officials said that heavy rains had begun at Teluk Bahang and Teluk Kumbar areas, about 9am today.
The supermoon phenomenon, which is expected to peak today is also expected to compound the situation by pushing floodwaters back inland.
As of 6.15am, 30 people from 13 families are being placed at community halls in the affected areas.
According to the Malaysian Meteorological Department, isolated thunderstorms are forecast for the rest of the day, until today midnight.
Yesterday, flash floods wreaked havoc on the island following a bout of heavy rain in the coastal eras of Teluk Bahang in the north and Bayan Lepas in the south.
The floods paralyzed traffic and grounded flights.