Tonga may expect up to two cyclones in the coming cyclone season, according to the latest meteorological prediction.

Tonga Met stated today that there is a 40-50% chance that at least one will be a Severe Tropical Cyclone (Category 3 or above).

The 2017/18 tropical cyclone season for Tonga begins on November 1 this year and runs through to April, 30 2018.

“The peak time for the occurrence of tropical cyclones in Tonga is from January to March, with most events occurring in February."

Tonga Met stated there is a high chance that any tropical cyclone affecting Tonga would approach from the Northern, Western and Southern sectors, that is with the expectation of tropical cyclone formation (genesis) to lie to the west of the Dateline towards the Coral Sea region.

About four to six named tropical cyclones are expected for the South West Pacific in the 2017/2018 season.

At the same time, tropical cyclones have occasionally formed outside this period like Tropical Cyclone Keli, which affected northern Tonga in June 1997.

South West Pacific

For this region, the La Niña-like signals in the ocean atmosphere system in the tropical Pacific Ocean have become more prominent in September this year, although have not yet reached the thresholds required for a La Niña event to be declared.

The Southern Oscillation Index (SOI) for September 2017 was positive at +0.6, on the La Niña side of neutral conditions. Wind observations also indicated enhanced trade winds, which is a pattern consistent with a developing La Nina.

Moreover, rainfall patterns in the tropical Pacific have become more La Niña-like than they were in August that is, more rainfall closer to Australia and drier than normal conditions about and east of the Dateline, stated Tonga Met.

The average number tropical cyclones that form in the Southwest Pacific is 8.1 during El Nino Years, 6.1 during La Niña and 6.3 during neutral years.

The outlook indicates that about four to six named tropical cyclones are expected for the South West Pacific in the 2017/2018 season, with the tropical cyclone activity expected to shift to the west in the coming season, consistent with cyclone tracks expected during La Niña.

Caution

Tonga Met said the information provided is only to be used as guidance and the given range of tropical cyclone numbers is indicative only.

"It is expected that the total number of tropical cyclones could be in the vicinity of the listed values, and not necessarily within the given range. The values are the most likely number of tropical cyclones based on statistical and scientific evidence, including the influences by regional and global weather and climate variability drivers and indices."

It advised that all communities should remain alert and prepared throughout the 2017-18 Tropical Cyclone Season and take heed of tropical cyclone alerts, warnings and advisories seriously whenever it is issued to reduce the effects on life and property.