Climate developments in August 2009
Enhanced South Pacific Convergence Zone (SPCZ) anomalies were largely absent from the region last month. Localised pockets of enhanced rainfall occurred in the North Tasman Sea and near Pitcairn Island. The Solomon Islands and Western Kiribati also had enhanced rainfall during August, while northeastern Australia was very dry. Suppressed convection existed southeast of Western Kiribati last month near Tuvalu, Tokelau, and the Northern Cook Islands. The regional circulation in August was characterised by more frequent low pressure south of Fiji, a deep low pressure anomaly south of the Australian Bight, and higher than normal pressure to the east of New Zealand. This pattern resulted in more frequent easterly and southeasterly anomalies across the southwest Pacific, particularly in the northern Tuamotu Archipelago region and the Marquesas. Southerlies were more frequent near New Caledonia.
High rainfall was recorded in the Solomon Islands, some locations in Papua New Guinea, the northern half of Vanuatu, and in Western Kiribati during August. For Western Kiribati this is the third month in a row with considerable rainfall, for the western island group, with Butaritari receiving 263mm (172% of normal). Except for Kiritimati Island in Eastern Kiribati, most stations along the Equator in Kiribati received well above normal rainfall. In Fiji, near normal to below normal rainfall occurred for 60% of stations that reported. Similarly, Samoa had average to below average rainfall for the month, while most stations in New Caledonia and the southern half of Vanuatu received well below normal rainfall in August.
In August dry conditions occurred over the northern and southern portions of French Polynesia. Significant rainfall anomalies (40 – 70% of normal) was recoreded in the Marquesas and in the Austral Islands, respectively. Gambier was the only region that received above normal rainfall during the month.
Warmer than normal conditions occurred as a whole across French Polynesia during August, with +0.6°C to +1.4°C above normal temperatures recorded. A new monthly mean temperature was also recorded for August at Tahiti. Maximum and minimum temperatures were also near or above normal for many other locations across the south Pacific. In New Zealand, it was the warmest August since records began 155 years ago.
Outgoing Long-wave Radiation (OLR) anomalies, in Wm2 are represented by hatched areas. High radiation levels (yellow) are typically associated with clearer skies and lower rainfall, while cloudy conditions lower the OLR (blue) and typically result in higher rainfall. The August 2009 position of the South Pacific Convergence Zone (SPCZ) could not be determined by OLR anomalies. Based on TRMM analysis, it was less coherent compared to previous months. The average position of the SPCZ is identified by the dashed green line, which is based on mean January rainfall for the South Pacific. Mean sea level (MSL) pressure anomalies (in hPa) are shown as solid and dashed black lines.
