Southwest Pacific Tropical Cyclone Outlook
Near normal tropical cyclone activity overall during November-April, but increased east and reduced west of the Date Line; multiple severe tropical cyclones expected.
Forecasters indicate another seven to 11 named tropical cyclones (TC) could occur in the Southwest Pacific basin between November and April, following the very early TC Liua that formed in September.
Analysis by forecasting centres across the Southwest Pacific show tropical cyclone activity is expected to be lower than normal around the northern and eastern Coral Sea margin and elevated east of the International Date Line.
New Caledonia, Fiji, Vanuatu and Tonga may experience two or more cyclones during the season. Three or four severe cyclones reaching Category 3 or higher are expected anywhere across the region during the season, which starts next month and officially lasts until the end of April.
On average, at least one ex-tropical cyclone passes within 550km of New Zealand each year. For the coming season, the risk for an ex-tropical cyclone New Zealand is considered near normal. If an ex-tropical cyclone comes close to the country, it has equal probability of passing east or west of Auckland and the North Island. Significant rainfall, extreme winds, hazardous marine conditions and coastal damage can occur leading up to and during these events.
Oceanic and atmospheric forecasts for ENSO (El Niño-Southern Oscillation) indicate El Niño conditions may develop by summer. At present, sea surface temperature anomalies across the central and eastern equatorial Pacific Ocean and atmospheric circulation patterns over French Polynesia and northern Australia indicate conditions bordering ENSO-neutral or leaning toward El Niño. It is worth noting that if El Niño develops it may be of the El Niño-Modoki (central Pacific based) flavour during early summer.
Islands on the fringe of the northern and eastern Coral Sea, including the Solomon Islands, Vanuatu, and New Caledonia may experience slightly decreased tropical cyclone activity. Increased TC activity is expected in some islands east of the International Date Line, especially those east of 160°W longitude, including Samoa, the Cook Islands, and the Austral Islands.
Tropical cyclones are categorised in strength from 1 to 5, with 5 being the most intense. For the coming season, about four storms are anticipated to reach at least Category 3 strength, with mean wind speeds of at least 118 km/h winds. Past years with conditions similar to present suggest some of these storm systems may increase to at least Category 4 strength, with mean wind speeds of 159 km/h. Category 5 strength cyclones, where winds are greater than 196 km/h, have occurred during years with similar conditions ahead of the 2018/19 season (known as ‘analogue’ seasons). Therefore, all communities should remain alert and well-prepared for severe events.
Tropical cyclones have a significant impact across the Southwest Pacific. Vanuatu and New Caledonia typically experience the greatest activity, with an average of two or three named cyclones passing close to land each year. For this season, the Southern Cook Islands and Samoa may experience 2-3 named cyclones, which is higher than average for those islands.
New Zealand should also be vigilant. During some analogue seasons used in the preparation of this outlook, multiple ex-tropical cyclones passed within 550 km of the country (including one during the early season prior to February). Significant wind, waves and rainfall are possible from these systems. Their effects can be spread over a larger area, particularly if the ex-tropical cyclone interacts with separate weather systems in the middle latitudes.
Tropical cyclone activity is expected to be slightly reduced for some countries during this season, especially for some islands west of the International Date Line. However, these islands typically experience multiple cyclones per year, and activity for those areas is still expected. All communities, regardless of changes in TC risk, should remain vigilant and be aware if the regional climate situation (including ENSO) changes. As with most years, activity is expected to increase during the second half of the season, from February-April. Early season activity is expected to be near normal.
NIWA, MetService, MeteoFrance, BoM, NOAA and Pacific Island National Meteorological Services will all continue to track the progression of ENSO and TC activity, with an update to this guidance in January 2019 if needed.
It does not take a direct hit or a severe cyclone to cause significant damage or life-threatening weather. When dangerous weather is forecast, please heed the advice of your local civil defence or disaster management offices.
New Zealand’s National Institute of Water & Atmospheric Research (NIWA) and Meteorological Service of New Zealand (MetService) along with contributions from 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.
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, Wallis, Futuna and New Caledonia, please contact MeteoFrance regional offices for information about how this guidance should be interpreted.