A heavy rain alert is now in force for the Eastern and Northern Division.
The Nadi Weather Office says a trough of low pressure lies slow moving just to the north of Fiji.
It is expected to drift south and affect the northern and eastern parts of the country from tomorrow and gradually affect the whole group later Thursday.
Some localised communities and businesses are likely to be affected with flash flooding of low-lying areas.
Localised flooding of iris crossings and informal settlements and disruption to traffic flow is also expected.