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Tonga expects 2 or 3 cyclones this season

Nuku'alofa, Tonga

Tonga could expect two to three cyclones this season, and Tonga Met says there's a chance that at least one of them could be a Severe Tropical Cyclone (Category 3 and above).

The current cyclone season began on 1 November and runs through to the end of April 2017.

Tonga Met says that tropical cyclones have occasionally formed outside this period, for example Tropical Cyclone Keli, that affected Northern Tonga in June 1997.

The tropical cyclone activity is likely to be slightly higher than average this season in Tonga, with the peak time from January to March. Most events take place in February, says the Meteorology Department in its new 'Tropical Cyclone Season Outlook 2016-17'.

Dry conditions

The report that assessments of the current El Nino Southern Oscillation (ENSO) indicate that near neutral conditions currently prevail in the Pacific Ocean and global models remain undecided whether a La Nina is likely to develop in late 2016 into the first half of 2017.

Tongan rainfall patterns in the last four to six-months have been erratic with extreme drought conditions experienced in some months and very wet conditions in some months. 

The outlook for the next six months is for normal conditions over most places.

Traditional knowledge indicates that when drought conditions are experienced ahead of the cyclone season, enhanced tropical cyclone activity is usually expected in the upcoming cyclone season.

An average of 10 to 12 tropical cyclones form in the Southwest Pacific each season.

Tonga's outlook indicates that eight to 10 named tropical cyclones are expected for the coming season, and tropical cyclone activity is elevated for island countries near Papua New Guinea and close to the International Date Line, near Tonga and Niue. Tonga is marked orange for "elevated risk" on the following graphic.

Tropical Cyclone Risk in 2016/17

Figure 1: Map of tropical cyclone risk for the number of named Cyclones interacting with an island group based on the 2016-17 Island Climate Update tropical cyclone guidance.

The outlook also reflects an expectation of overall elevated activity during both the early season (November to January) and the late season (February to April), particularly west of the Dateline.

Tropical cyclone activity outlook for islands like New Caledonia, Fiji, Vanuatu and Tonga indicates two or more cyclones could interact with each of those countries during the season despite subtle projected differences from normal.

At least five to six severe tropical cyclones (Category 3 or higher) are expected to occur anywhere across the Southwest Pacific during the season.

"All communities should remain vigilant and follow forecast information provided by the Meteorology Department throughout the season," Tonga Met advised.

In the following graphic, Tonga is marked red for 2 to 3 cyclones in this season's outlook.

Tropical Cyclone Outlook 2016-17

Figure 2: Map of tropical cyclone overall seasonal outlook for the number of named cyclones interacting with an island group based on the 2016-17 Island Climate Update tropical cyclone guidance.