The Fiji met service has issued a tropical cyclone warning for Tonga.
The metservice says tropical depression 15F, which has caused heavy rain in Fiji, is about 537 kilometres west-northwest of Vava'u or 555 kilometres northwest of Nuku'alofa.
It says the system is moving south-southeast at about 10 knots, and is expected to intensify further and possibly become a tropical cyclone in the next 6 to 12 hours.