Climate developments in October 2009
The South Pacific Convergence Zone (SPCZ) was contracted toward Papua New Guinea this month, and was poorly defined to the northwest of Fiji and east of the dateline. Overall, the displacement of the north-western, tropical portion of the SPCZ was further south and west than normal for October. However TRMM rainfall monitoring indicates the central and eastern sub-tropical components of the SPCZ are now shifting northeast. A small region of suppressed convection extended from near Samoa southeast to the Austral Islands. The regional circulation was characterised by lower than normal pressures over French Polynesia, and higher than normal pressures over Australia. This pattern is similar to what might normally be seen during El Niño in the Austral spring, and it brought southerly quadrant wind anomalies and negative temperature anomalies to many island countries last month.
Rainfall was well below average for many island nations in the southwest Pacific as a result of the atmospheric developments linked to El Niño. Most stations in New Caledonia received between 20–60% normal rainfall, and similar anomalies were observed nearby for the islands in the Tasman Sea. Many stations in Fiji reported dry conditions, with the exception of Rotuma in the far north which had very high monthly rainfall. A similar story was reported for Vanuatu, which had anomalies of 40–60% of normal in the southern and central part of the island group and well above normal rainfall in the north at Sola (516mm; 143% of normal). Wallis and Futuna, Tonga, and Niue also reported very dry conditions for the month.
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 results in higher rainfalls. The October 2009 position of the South Pacific Convergence Zone (SPCZ), as identified from OLR , is indicated by the solid green line. Overall, the SPCZ was contracted toward Papua New Guinea, and the sub-tropical portion has now started to swing north. The SPCZ was poorly defined in the OLR anomalies east of Vanuatu this month. The average position of the SPCZ is identified by the dashed green line.
