Near Average Tropical Cyclone Season expected

11/10/19

Near Average Tropical Cyclone Season expected for Southwest Pacific

A ‘near-average’ Tropical Cyclone Season is forecast this year, with 9 to 12 named cyclones expected to occur in the Southwest Pacific between November and April. About four of these may be severe, reaching category three or higher. New Zealand however is typically only affected by one ex-tropical cyclone on average and the coming season is expected to be ‘normal’.

Every year MetService, New Zealand’s official Tropical Cyclone Warning Centre (TCWC), works alongside NIWA, Australia’s Bureau of Meteorology and national meteorological services from other Pacific nations to produce a Tropical Cyclone Outlook for the coming season.

“The average number of named tropical cyclones in the Southwest Pacific (including the Coral Sea) is about 10 per season,” says TCWC Manager and Severe Weather Expert Chris Noble. “This season, cyclone activity is expected to be near average,” he adds.

MetService will begin to issue its daily Tropical Cyclone Potential Bulletin from 1st November, or earlier if there is a pre-season development. The bulletin will be published on the Metservice website at https://www.metservice.com/warnings/tropical-cyclone-activity

“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 as we saw last year with Liua in September.”

“This coming season, the El Niño Southern Oscillation (ENSO) cycle is expected to be neutral but with a possible weak warm bias. This leads to a forecast of more cyclone activity than normal east of the International Date Line and especially late in the season,” says Chris.

“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. It does not take a direct hit or a severe cyclone to cause significant damage or life-threatening weather. If severe weather is forecast, we urge the public to follow official advice from national meteorological services, disaster management offices or local civil defence.”

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 and may even cross New Zealand, such as the memorable cyclones Fehi and Gita in 2018 that brought severe weather along with storm surge and coastal inundation to parts of the country.

If cyclones are expected to impact New Zealand with severe weather, official advice will be provided via Severe Weather Outlooks, Watches and Warnings issued by MetService. Even if land areas are not affected, warnings are still issued for vessels over the open sea.

For more information on Tropical Cyclones including Category ratings, visit https://about.metservice.com/our-company/national-weather-services/tropical-cyclones/

For the full report go to: https://www.niwa.co.nz/climate/southwest-pacific-tropical-cyclone-outlook/southwest-pacific-tropical-cyclone-outlook-october-2019

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