The 2016/2017 Tropical Cyclone season officially commenced on 1 November 2016. As usual the relevant authorities for the Pacific region have issued tropical cyclone outlooks for the coming season, and this report reviews the various forecasts made.
Firstly, let us consider the global climate pattern this season. The El Niño / Southern Oscillation (ENSO) is the primary driver of inter seasonal variation of tropical cyclogenesis in the south west Pacific. To put this in language more easily understood, each year the number of tropical cyclones, the likelihood of severe tropical cyclones, and the preferred area for them to form changes, and the main reason for this is the changes in sea temperature around the south Pacific Ocean. Whereas last season (2015/2016) and also the season before that, strongly warm (El Niño) climate conditions dominated, with one of the strongest ever El Niño events ever recorded occurring during the 2015/2016 season.
That event ended in the first quarter of 2016, and the 3 month period from July to September 2016 inclusive were characterised by near neutral to weak La Niña conditions across the Pacific region. International Climate Model Guidance indicates that the most likely outcome for the 2016/17 season is for neutral conditions to prevail, perhaps tending to weakly La Niña, and the seasonal outlook is therefore based on this basic assumption.
Tropical Cyclone activity in the 2016/17 season within the tropical south west Pacific region from the equator to 25˚ South latitude and between 160˚ East longitude and 120˚ West longitude (from the Solomon Islands to east of French Polynesia) is anticipated to be near average. As the near neutral climate conditions are relatively common, over all confidence in this forecast is high.
Five to seven (5 to 7) tropical cyclones are expected to occur in the large expanse of the Pacific described above.
The average for all the 47 seasons from 1969-70 to 2015-16 is 7.3 cyclones. The average for El Niño, La Niña and neutral seasons are 8.7, 6.5 and 6.4 tropical cyclones respectively.
Historically, neutral ENSO conditions result in a westward shift in tropical cyclone activity in the Southwest Pacific, hence the preferred region for the formation of tropical cyclones this season will be over waters west of the 180 meridian of longitude – basically from Fiji westwards. This is not to say that cyclones will not form at all over waters east of Fiji, but the overall risk will be lower. The risk of severe tropical cyclones developing is near normal, with about 1 or 2 typical. That said, in recent seasons the number of severe cyclones as a percentage of the total number observed has been higher than normal. This may be a consequence of climate change, or alternatively it may just be a statistical anomaly.
Around Fiji the risk of tropical cyclone formation is likely to be slightly higher than normal, and this season we anticipate two to three cyclones will pass through Fiji waters.
It is likely that at least one of these will be severe (category 3 status or higher).
As mentioned above, the preferred area for tropical cyclone development will be west of the date line and the warm waters of the Coral Sea (from the northeastern coast of Australia to Vanuatu, between the Solomon Islands and New Caledonia is typically where many of the cyclones in our region form. On this basis, there is high chance that Tropical Cyclones will approach Fiji from the Western and Northern sectors.
Some tropical cyclones passing close to Fiji but not directly over Fiji waters have been known to bring active cloud and rain bands that can occasionally cause prolonged heavy rain and accompanying flooding. This includes tropical depressions, low pressure systems not yet strong enough to be categorized as a tropical cyclone. Typically three or four tropical depressions affect Fiji in a season, additional to those named tropical cyclones. (Valium)
The only way to deal with tropical cyclone hazards is to be prepared and have a response plan ready to implement when a threat develops.
Here’s hoping for a safe and uneventful cyclone season this summer.
Sincerely,
