Southwest Pacific Tropical Cyclone Outlook: Strong El Niño expected to produce above average activity and severe
tropical storm impacts
Meteorological and climate analysis centres across the Southwest Pacific are indicating above average numbers of
tropical cyclones (TC) for the 2015–16 season (November 2015 to April 2016). The 30-year average number of all Southwest
Pacific tropical storms that formed between 1981-2010 is 12.4 for the November and April TC season. The average number
of storms that developed into named TCs (Category 1 or stronger) during the same interval is 10.4 for the SW Pacific
basin . The outlook indicates that 11 to 13 named TCs are expected for the coming season. TC activity is elevated for a
majority of the Pacific Island countries, especially those situated close to or east of the International Date Line
It should be recognised that the six-month outlook reflects an expectation of overall elevated activity during both the
early season (November to January) and the late season (February to April) particularly east of the Dateline. Note that
the TC activity outlook for islands like New Caledonia 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 six severe TCs (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 their national meteorological service.
On average, New Zealand experiences at least one ex-tropical cyclone passing within 550km of the country every year. For
the coming TC season, the risk for New Zealand is slightly higher than normal. If an ex-tropical cyclone comes close to
the country, the current background climate conditions suggest it has an equal probability of passing east or west of
Auckland city. Significant rainfall, damaging winds and coastal impacts can occur leading up to and during these
episodic events.
Outlook analysis
Conditions associated with a strong El Niño are indicated by sea surface temperature anomalies across the central and
eastern Equatorial Pacific Ocean, and the atmospheric circulation patterns that exist over French Polynesia and northern
Australia. There is an expectation amongst a number of international forecast centres that the present El Niño event
will be one of the strongest in the last 60 years. The current event still has the potential of surpassing the 1997/98
event. Taking this climate scenario into account, elevated TC activity can be expected for many islands in the Southwest
Pacific during the 2015–2016 season, with 11 to 13 named TCs forming across the region during the November 2015–April
2016 period.
Southwest Pacific TCs are grouped into classes ranging from 1 to 5, with 5 being the most dangerous. For the coming TC
season, at least six storms are anticipated to reach at least Category 3, with mean wind speeds of at least 64 knots or
118 km/h (so-called ‘hurricane force’ winds). Of those systems, four storms may reach at least Category 4 strength, with
mean wind speeds of at least 86 knots or 159 km/h. In addition, Category 5 strength TCs (winds greater than 106 knots or
196 km/h) are known to occur during seasons like the current one. Therefore, all communities should remain alert and
well prepared for severe events.
Tropical cyclones have a significant impact across the Southwest Pacific from year to year. Vanuatu and New Caledonia
typically experience the greatest activity, with an average of 2 or 3 TCs passing close to land each year and there are
indications that activity may be above average this season for many islands, including Vanuatu, Fiji, and Wallis & Futuna. The outlook indicates elevated TC activity for the 2015–16 season for many islands east of the International
Date Line that is typically associated with El Niño with reduced risk for Papua New Guinea. Elevated risk is forecast
for countries east of the International Date Line include Tokelau, Samoa, Tuvalu and further east in the Northern Cook
Islands, the Southern Cook Islands, and more broadly across French Polynesia.
On average, New Zealand usually experiences at least one interaction per season with an ex-tropical cyclone during El
Niño conditions. Most of the analog seasons identified for this forecast (1972/73; 1982/83; 1987/88; 1991/92; 1997/98 )
show multiple ex-tropical cyclones coming close (within 550 km) to the country. Significant wind, waves and rainfall are
possible from these systems. Their effects can be spread over a larger area when the ex-tropical cyclone interacts with
separate weather systems.
Even though TC activity is expected to be relatively low for some countries, historical cyclone tracks (see supporting
information for this forecast, Figure 3) indicate that TCs can affect all parts of French Polynesia (including the
Society Islands, the Austral Islands, the Tuamotu Archipelago, and the Marquesas).
All Pacific Islands should remain vigilant in case conditions in the equatorial Pacific change during the TC season.
Past El Niño seasons have seen TC tracks with increased sinuosity (irregular or looping motions rather than a
curvilinear trajectory), which means they have potential to impact a large area.
New Zealand’s National Institute of Water & Atmospheric Research (NIWA) and Meteorological Service of New Zealand (MetService) along with meteorological
forecasting organizations from the Southwest Pacific, including the Australian Bureau of Meteorology, MeteoFrance and
the Pacific Island National Meteorological Services have prepared this tropical cyclone outlook.
ENDS