A heavy rain alert is now in force for eastern half of Viti Levu, southern Bua, Cakaudrove and northeastern Macuata provinces, Lau and Lomaiviti Groups, Beqa, Vatulele, Kadavu and nearby smaller islands.
In a statement, the Fiji Meteorological Services say occasional rain, heavy at times, and isolated thunderstorms expected in these areas from later tonight.
The Nadi Weather Office said localised heavy falls may lead to flash flooding of low-lying and flood prone areas.
A trough of low pressure is expected to develop to the east of Fiji and affect parts of the group from later today and continue until the next few days.
Another trough of low pressure lies slow moving to the southwest of Fiji and is gradually drifting southeast towards the group.