UPDATED: A cyclone warning has been issued for Tonga’s outer islands of Vava’u and Ha’apai, with Fua'amotu Tropical Cyclone Warning Centre saying a heavy rain advisory remains in force for all of Tonga.

The Nadi Tropical Cyclone Centre in Fiji says a tropical cyclone named "Ian", is heading south towards the island groups of Ha'apai and Vavau.

A tropical cyclone alert is now in force for Vava'u and Ha'apai groups.

A gale alert is now in force for  Vava'u and Ha'apai groups.

A strong wind warning remains in force for Ha'apai and Vava'u.

FTCWC says a tropical depression 07f was located near 19 decimal 0 south 175 decimal 6 west or about 170km west southwest of Vava'u or about 160km northwest Lifuka at 1am this morning.

Tropical depression 07f has estimated winds of 25-30 kt near its centre and is currently slow moving but expected to move south southeast in the next 12 to 24hrs.

The system is slowly intensifying and could possibly become a tropical cyclone in the next 24 to 48 hours.

On this track,and if the depression continues to intensify, it may bring damaging gale force winds over Vava'u and Ha'apai groups in the next 24  to 48hrs.

Forecast to midnight tonight for Tonga

For Vava'u and Ha'apai group:

Moderate to fresh north to northwest winds becoming strong and gusty. rain developing, becoming heavy at times.

For the rest of Tonga:

Light to moderate northwest winds about the Niuas. Mostly cloudy with occasional showers with some heavy falls expected.

For Tongatapu and Eua, light to moderate east winds becoming moderate to fresh north to northeast winds. Mostly cloudy with occasional showers heavy at times.