Climate developments in January 2010

Climate developments in January 2010

Enhanced convection along a partially northeast displaced South Pacific Convergence Zone (SPCZ) were seen to the south of the Tuamotu Archipelago this past month. Likewise, convection along the Equator generated significant rainfall in Western Kiribati, Eastern Kiribati, and Nauru. Suppressed convection existed in the central portion of the southwest Pacific, particularly around Vanuatu, Fiji, Tonga and in the Marquesas. The regional circulation in January was characterised by more frequent low pressure in the eastern sector of French Polynesia, and and higher than normal pressure to the north and east of New Zealand and over eastern Australia. This pattern resulted in more frequent southeasterly anomalies across the much of southwest Pacific.

Very high rainfall was recorded at stations in French Polynesia, northern Australia, parts of Papua New Guinea, and Western Kiribati this past month, either due to convection associated with the Intertropical Convergence Zone (ITCZ), SPCZ, or monsoonal trough. In Eastern Kiribati, 781mm (724% of normal) of rain fell during January, a record high. It is the seventh month in a row with considerable rainfall at Tarawa (>190 % of normal). In Papua New Guinea, more than one meter of rainfall was recorded at Hoskins, due to monsoon trough activity, and infrastructure including roads and bridges were destroyed by flooding. High rainfall in French Polynesia was also contributed to movement of the SPCZ over the region during the month. TC Oli, which formed very late in January, and a northeast-displaced subtropical limb of the SPCZ contributed to high totals in Gambier and Bora Bora.

Many regional rainfall developments were characterised by drier than normal conditions for island groups in the central part of the southwest Pacific due to the continuation of El Niño during January. Well below normal rainfall occurred over most of Vanuatu, New Caledonia, and especially Fiji last month. Particularly dry conditions were observed in the Austral Islands and Marquesas with as low as 15% of normal rainfall recorded in that area.

Warm conditions also affected all of French Polynesia during January, with anomalies of more than +1.5°C in Tahiti. Temperatures wera also above average in southeastern Australia during January.

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 January 2010 position of the South Pacific Convergence Zone (SPCZ) was northeast of normal to and particularly active south of the Tuamotu Archipelago. The average SPCZ position 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.