Monthly climate

Climate developments in October 2005

Outgoing Long-wave Radiation anomalies for October 2005. (Click for enlargement and detail)

An area of enhanced convection affected Papua New Guinea and also the northeast of Australia. The SPCZ extended from the region near the Solomon Islands towards Samoa and the Southern Cook Islands. The Inter-tropical Convergence Zone (ITCZ) was well north of the equator. Suppressed convection existed from Vanuatu east to Pitcairn Island, including Fiji, Tuvalu, Wallis and Futuna, Samoa, Tokelau, the Northern Cook Islands, and the Society Islands of French Polynesia.

Rainfall was more than 200% of average in the east of Fiji’s main island (where more than 135 mm occurred on 29th October) and parts of Tonga, and at least 125% of average in Niue and parts of southern French Polynesia. October rainfall was less than 75% of average in central French Polynesia, and less than 50% of normal throughout much of Vanuatu and New Caledonia.

Mean air temperatures were more than 1.0 °C above average in the Southern Cook Islands, about 1 °C above average in Western Kiribati, Tuvalu, and much of central and southern French Polynesia, and at least 0.5 °C above average in Fiji, Wallis and Futuna, and northern Tonga. In contrast, they were about 0.5 °C below average in Vanuatu.

Tropical Southwest Pacific mean sea level pressures continued below average, within about 10° north and south of the equator, east of the Date Line. However, they were above average over much of French Polynesia. Equatorial surface easterlies were persistent along the equator, occurring in about 90% of observations at Tarawa.

Sea surface temperature anomalies (°C) for October 2005. (Click for enlargement)

Mean sea surface temperatures (°C) for October 2005. (Click for enlargement)

The tropical Pacific Ocean is in a neutral state (no El Niño or La Niña), although sea surface temperatures near the Date Line remain somewhat above average. The Southern Oscillation Index (SOI) was positive in October (+1.0), but the 3-month August-October average remained near zero (+0.1). The NINO4 sea surface temperature (SST) anomaly in October was about +0.6 °C, showing little change from September. The NINO3 SST anomaly remained small (+0.1°C), with negative anomalies near the South American coast. The cold subsurface temperature anomaly at about 100 m depth and 140 °W has also shown little change from September. Other indicators show typical climatological patterns, with no pronounced anomalies apparent in surface winds or convection (OLR).

Almost all available models indicate neutral conditions through to the end of autumn 2006. The Scripps/MPI dynamical model continues to develop a warm SST anomaly in the central Pacific, but this is not as pronounced in the latest model run as in the past three months. The latest US National Center for Environmental Prediction statement (6 October) is for neutral conditions over the next 3-6 months. The US International Research Institute for Climate Prediction summary gives a 95% chance of neutral conditions persisting through to the end of 2005, and only a 1% chance of La Niña in this time period.