Feature article

The Southwest Pacific Climate in 2003

Stuart Burgess and Dr Jim Salinger, NIWA

The 2002/03 El Niño event, although decaying, had a significant impact in the Southwest Pacific. The event commenced in May 2002, had weakened by January 2003, and dissipated by April (Fig.1).This had a noticeable impact on the Southwest Pacific rainfall anomalies at the beginning of the year with above average rainfall over Eastern and Western Kiribati until it dissipated in April, and below average rainfall over much of New Caledonia and Fiji during the first few months of 2003. Southwest Pacific rainfall patterns were dominated by other features during the remainder of the year. The trade winds increased in strength from February, except for a westerly wind burst that occurred in October. Generally, higher than average sea surface temperature (SST) anomalies occurred throughout the region during 2003 (Fig. 2). Nine tropical cyclone occurrences, five of which were classified as major hurricanes, affected the region.

Both sea surface temperatures (SSTs) and mean air temperatures were at least 0.5°C above average throughout much of the tropical Southwest Pacific, especially along the equator from Nauru to the north of Rawaki Island, Eastern Kiribati where they were about 1.0°C above average. The year was one of the warmest on record for mean air temperatures in the Marquesas (+0.9°C above average at Hiva Hoa) and Tuamotu Islands (+0.7°C above average at Takaroa) of French Polynesia.

Above average air pressures in the Coral Sea suppressed convection in that area, including southern parts of the Solomon Islands, northern Vanuatu, and toward the Date Line.Suppressed convection also occurred in an extensive region along the equator from the Date Line east toward South America, including Eastern Kiribati and the Marquesas Islands (Fig. 3). The 2003 rainfall total at Willis Island (358 mm) was only 32% of average, and extremely low. Ono-i-Lau in Fiji recorded 1068 mm, 65% of average, with Hiva Hoa in the Marquesas Islands recording 751 mm, 62% of average, and one of the lowest annual rainfall totals on record.

Areas of enhanced convection affected the region north of Papua New Guinea, the Marshall Islands, and parts of southern French Polynesia. For the year, the South Pacific Convergence Zone (SPCZ) was generally further north and east than usual. However, its main area of activity was concentrated in areas east of the Date Line from February to May, moving to areas west of the Date Line from September to November. Rainfall was above average in parts of New Caledonia, Tonga, and the southern Cook Islands.

Fig 1: The Southern Oscillation Index (SOI). The coloured bars show monthly standard deviations (blue for positive, red for negative).

Fig 2: 2003 climate patterns. Sea Surface temperature (SST) anomalies (departure from average ,°C) . Yellow or orange areas represent warmer than average seas.

Fig 3: 2003 climate patterns. OLR anomalies. Yellow or orange represents suppressed convection.