11 October 2017
Tropical Cyclone activity expected to be near-normal this season
The Southwest Pacific tropical cyclone season formally starts on the 1st of November, with an average number of named
cyclones expected in the upcoming 2017-18 season under the influence of climate conditions heading into La Niña this
summer.
Every year MetService works alongside NIWA and national meteorological services from other Pacific nations to produce a
Tropical Cyclone Outlook for the upcoming season. The outlook for the 2017-18 season indicates 8 to 10 named cyclones
are expected in the Southwest Pacific, with about 4 of those expected to be severe (Category 3 or higher). The average
number of named tropical cyclones in the Southwest Pacific (including the Coral Sea) is about 10 per season.
This year, with the El Nino Southern Oscillation (ENSO) cycle tending to La Nina conditions, tropical cyclone activity
is expected to be higher than normal around the Coral Sea and west of the International Date Line, and lower further
east. For New Zealand, which is affected by about one ex-tropical cyclone on average per season, the risk is expected to
be normal to slightly above normal.
Around the globe, the role of monitoring and warning for tropical cyclones is performed by a WMO designated Regional
Specialized Meteorological Centre (RSMC) or a Tropical Cyclone Warning Centre (TCWC), depending on the location of the
cyclone. TCWC Wellington, based at MetService, has warning responsibility for the area that extends from 160E to 120W
between 25S and 40S. Although it is very rare for a tropical cyclone to form in the TCWC Wellington area of
responsibility, intense tropical cyclones do arrive from the neighbouring Brisbane or Nadi areas and they often retain
their named cyclone status until near 30S. Sometimes an ex-tropical cyclone will approach New Zealand and the official
Severe Weather Watches and Warnings need to be issued by MetService. Even if land areas are not affected, warnings are
still issued for vessels over the open sea.
Satellite image courtesy of JMA.
Although the tropical cyclone season typically runs from the start of November until the end of April, cyclone
development doesn’t always follow the calendar and cyclones can form outside the season. All communities throughout the
South Pacific, including New Zealand, are encouraged to prepare for the coming cyclone season and remain vigilant for
developing cyclones or other severe weather. You can keep up to date with current and expected tropical cyclone activity
on the MetService website at http://info.metraweather.com/e/60812/ings-tropical-cyclone-activity/f5m1l6/612683765 where
a TC Potential Bulletin will be issued daily from 1st November, or earlier if necessary.
ends