Southwest Pacific Tropical Cyclone Outlook

Southwest Pacific Tropical Cyclone Outlook

Near average tropical cyclone numbers for the region is likely, with increased activity in the late season.

Meteorological forecasting centres across the Southwest Pacific are predicting near average numbers of tropical cyclones for the 2013–14 season (November 2013 to April 2014).

On average, 10 named tropical cyclones occur in the Southwest Pacific {between 135°E (mid-Gulf of Carpentaria) and 120°W (French Polynesia)} each season (November to April).

The outlook indicates that eight to 12 named cyclones are expected for the coming season.

Tropical cyclone (TC) activity between Vanuatu and New Caledonia as well as east of the International Date Line is expected to be normal or below normal over the whole of the season. Normal or slightly above normal activity is expected for countries close to the International Date Line and near the Gulf of Carpentaria.

Most countries west of the International Date Line, including Papua New Guinea, the Solomon Islands, and Fiji are likely to experience close to normal activity because of ENSO-neutral conditions.

It should be recognised that increased activity in general is expected as the TC season progresses. Note that the forecast of normal activity for islands like New Caledonia, Vanuatu, Fiji, and Tonga indicates two or more cyclones could interact with each of those countries during the season.

At least one or more severe tropical cyclones (Category 3 or higher*) could 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, it has a higher probability of passing east rather than west of Auckland city.

Outlook analysis

ENSO neutral conditions are indicated by sea surface temperature anomalies across the central and eastern Equatorial Pacific Ocean, and the atmospheric circulation patterns over French Polynesia and northern Australia.

The expectation is that near normal tropical cyclone (TC) activity is likely for most islands in the Southwest Pacific during the 2013–2014 season. TC activity is expected to be near average with eight to 12 named TCs over the November 2013–April 2014 period for the Southwest Pacific.

On average,10 tropical cyclones occur each year for the Southwest Pacific region. 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 four storms are predicted 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, three storms may reach at least Category 4 strength, with mean wind speeds of at least 86 knots or 159 km/h.

While Category 5 strength TCs have not been prominent for ENSO neutral seasons like the current one, this type of event is still possible. All communities should remain alert and prepared for such an event.

Tropical cyclones significantly impact the Southwest Pacific each year. Countries like Vanuatu and New Caledonia typically experience the greatest activity, with an average of about two or three TCs passing close to land there each year.

The forecast for this season indicates near normal or slightly reduced tropical cyclone activity for the 2013–14 season for many islands east of the International Date Line and also for the region between Vanuatu and New Caledonia.

Near normal TC activity is expected for countries situated close to the International Date Line including Fiji, Samoa, Tonga, while slightly elevated activity is expected for Niue and New Zealand.

On average, New Zealand usually experiences at least one interaction per season with an ex-tropical cyclone during ENSO neutral conditions.

Most of the analog seasons identified for this forecast (1978/79; 1979/80; 1980/81; 1981/82; 1990/91; 1996/97; 2001/02) show an ex-tropical cyclone coming close (within 550km) 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 meets a higher latitude high pressure system.

Even though TC activity is expected to be near normal or below normal for some countries, historical cyclone tracks (see supporting information for this forecast, Figure 2) indicate that TCs can affect parts of French Polynesia (including the Society Islands and the Austral Islands) and the Southern Cook Islands, especially late in the TC season.

As with the majority of other years, the late TC season (February–April) is expected to be the most active time in the Southwest Pacific.

All Pacific Islands should remain vigilant in case conditions in the equatorial Pacific change during the tropical cyclone season. Past ENSO neutral seasons have seen tropical cyclone tracks with increased sinuosity (irregular or looping motions rather than have a curvilinear trajectory), which means they have potential to impact a large area.

Nealand’s National Institute of Water & Atmospheric Research (NIWA) and Meteorological Service of New Zealand (MetService) along with meteorological forecasting organisations from the Southwest Pacific, including the Australian Bureau of Meteorology, and the Pacific Island National Meteorological Services have prepared this tropical cyclone outlook.
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