Cook Islands + 6 more

Pacific Cyclone and Precipitation Outlook 2010-2011

Originally published


*The Pacific region is currently experiencing the weather phenomenon La Niña, which is projected to continue into February - April 2011. La Niña typically affects the distribution of rain and tropical cyclones across the region. Map 1 shows the areas with higher and lower precipitation in Asia and the Pacific during La Niña, in boreal summers (June to August) and boreal winters (December to February).

*Above normal rainfall is expected for Fiji, Papua New Guinea, New Caledonia, Vanuatu, Niue, Tonga and the Southern Cook Islands for the coming three month period. Near (or above) average rainfall is forecast for Wallis & Futuna, Samoa, and the Austral Islands. Near normal rainfall is forecast for the Society Islands and the Solomon Islands. Below average rainfall is predicted for Western and Eastern Kiribati, Tuvalu, Tokelau, the Tuamotu islands and Northern Cook Islands. Map 2 illustrates which countries may face a heightened risk of flood or drought.

*The expectation is that normal or above normal tropical cyclone activity will occur for most islands west of the International Date Line in the southwest Pacific during the November 2010 - April 2011 season. Projections show an increased risk of tropical cyclones over the Coral Sea and to the southwest of Fiji, particularly for Papua New Guinea, the Solomon Islands, Vanuatu, and New Caledonia.

*While risk is generally reduced for islands to the east of the International Date Line during La Niña, historical cyclone tracks indicate that tropical cyclones can affect parts of southwest French Polynesia, including the Society and Austral Islands, and the Cook Islands during La Niña. Map 3 gives an historical overview of tropical storm tracks in the southwest Pacific, highlighting tropical storm tracks in past La Niña years.

*Nine to 12 named tropical cyclones are expected over the coming season for the southwest Pacific. Southwest Pacific tropical cyclones are grouped into classes ranging from 1 to 5, with 5 being the most dangerous. For the coming season, three cyclones are forecast to reach at least Category 3, and one system is expected to reach at least Category 4, with mean wind speeds of at least 64 knots or 118 km/h.

Background on La Nina

Since June 2009, the Pacific region has been experiencing a weather phenomenon called La Niña. This current La Niña has been rated as moderate -strong, and is projected to impact tropical cyclone development and trajectory, as well as rainfall distribution across the Pacific Region. Historically, during La Nina, tropical cyclones are concentrated to the west of the International Dateline. Map 4 shows the typical changes in precipitation and tropical storm patterns through-out the Southwest Pacific cyclone season (on a month-by-month basis from November to February), based on historical data.

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