Southwest Pacific Tropical Cyclone Outlook: Near average or slightly above average numbers for many islands likely, and increased activity in the late season near Tonga and Niue

Meteorological forecasting centres across the Pacific are predicting near average or slightly above average numbers of tropical cyclones for the 2012–13 season (November 2012 to April 2013). On average[1], 10 named tropical cyclones occur in the southwest Pacific (between 135°E and 120°W) each season (November to April). The outlook indicates that 9 to 12 named cyclones are expected for the 2012 – 2013 season. Tropical cyclone activity east of the International Dateline is expected to be normal, with above normal activity for Niue and Tonga during the second half of the season.

Most countries west of the International Date Line, including Papua New Guinea, the Solomon Islands, Vanuatu, New Caledonia and Fiji are likely to experience close to normal or slightly above normal activity because of ENSO-neutral conditions. It should be recognised that increased activity to the west of the Dateline is expected as the season progresses. Note that the forecast of normal or above normal activity for islands like New Caledonia, Vanuatu, Fiji, and Tonga indicates two or three tropical cyclones interacting with each of those countries during the season can be expected. At least one or more severe tropical cyclones (Category 3 or higher[2]) could occur anywhere across the southwest Pacific during the season. All communities should remain vigilant.

On average, New Zealand experiences at least one ex-tropical cyclone passing within 550km of the country every season and this threat applies during the coming season.

Outlook analysis

ENSO neutral conditions currently exist in the region. Sea surface temperature anomalies across the central and eastern Equatorial Pacific Ocean are near normal (warmer than normal but not reaching El Niño thresholds), and the atmospheric circulation patterns over French Polynesia and northern Australia are only weakly reminiscent (if at all) of El Niño. The expectation is that normal tropical cyclone (TC) activity is likely for most islands in the southwest Pacific during the 2012–2013 season. TC activity is expected to be near average with 9 to 12 named TCs over the November 2012–April 2013 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 two cyclones are predicted to reach at least Category 3, with mean wind speeds of at least 64 knots or 118 km/h. One system 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 identified as past analogs to this coming season, the most recent analog has suggested this type of event is still possible. All communities should remain alert and prepared for such an event.

Each year, tropical cyclones have a significant impact on the southwest Pacific. Places like Vanuatu and New Caledonia typically experience the greatest activity in the region, with an average of about 3 or 4 TCs passing close to those countries each year. The forecast for this season indicates near normal to slightly increased tropical cyclone activity for the 2012–13 season for eastern Papua New Guinea, the Solomon Islands, Vanuatu, New Caledonia, Tonga and Niue, but near normal activity for most other islands east of the Dateline.

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; 1990/91; 1996/97; 2001/02; 2003/04) show an ex-tropical cyclone coming close (within 550km) of the country. Significant wind, waves and rainfall are possible from these systems, and their effects can be spread over a larger area when the ex-tropical cyclone impinges on a higher latitude high pressure system.

Even though TC activity is about average for islands east of the International Date Line during ENSO neutral conditions, historical cyclone tracks (see supporting information for this forecast, Figure 2) indicate that TCs can affect parts of southwest French Polynesia, including the Society and Austral Islands, and the Southern Cook Islands, especially late in the TC season. As with the majority of TC seasons, the late season period (February–April) is expected to be the most active time for TCs in the southwest Pacific.

All Pacific Islands should remain vigilant in case the warm conditions in the equatorial Pacific strengthen during the tropical cyclone season. Should a weak El Niño develop (which seems unlikely at present), the TC risk east of the International Dateline is expected to increase. During ENSO neutral analog seasons (see explanation of analog selection below), tropical cyclones are usually reclassified as a mid-latitude type of depression within ±10° of the Dateline.

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, and the Pacific Island National Meteorological Services have prepared this tropical cyclone outlook.

Contacts for comment

In New Zealand:
Dr Andrew Lorrey
Climate Scientist, NIWA
Tel: +64 9 375 2055

Dr Nicolas Fauchereau
Climate Scientist, NIWA
Tel: +64 9 375 4553

Mr. Steve Ready
Manager, Wellington RSMC (Regional Specialized Meteorological Centre)
MetService New Zealand
Tel: +64 4 4700 737

In the Pacific Islands, please contact your local national meteorological service for information about how this guidance should be interpreted.

For Australia and associated offshore islands, please contact the Australian Bureau of Meteorology for information about how this guidance should be interpreted

For French Polynesia and New Caledonia, please contact MeteoFrance for information about how this guidance should be interpreted

[1] The long-term 42-year average from 1970-201, was obtained from the South Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) available at http://apdrc.soest.hawaii.edu/projects/speartc/

[2] See http://www.bom.gov.au/cyclone/about/intensity.shtml