A heavy rain alert is now in force for the whole of Fiji.

The Fiji Meteorological Office says an active trough of low pressure with associated cloud and rain is gradually approaching the group from the northwest of Fiji.

It says that this expected trough is anticipated to produce occasional to periods of rain, heavy at times, and thunderstorms over most parts of the group from tomorrow till Friday.

The weather office says consequently, a heavy rain alert is now in force for the whole of Fiji.

Localised heavy falls may lead to flash flooding of low lying and flood prone areas with the chance of river flooding.

The weather office reiterated that during this time of the year there is also abundance of moisture in the environment and with more heating, afternoon and evening thunderstorms risk is elevated.

Conditions are expected to ease from later Friday, but isolated heavy falls with thunderstorms in the afternoon and evening may continue.