The system, to the country's west, is already whipping up strong winds and rough seas across much of the country.
The Vava'u islands have already seen winds in excess of 100 kilometres an hour.
Foleni Tu'uholoaki, from Tonga's Meteorological Service, said while the system isn't forecast to pass close, the islands are sandwiched between two pressure systems that are funnelling winds over Tonga.
