Feature article
Tropical Cyclones
Only three tropical cyclones so far
Three tropical cyclones have occurred so far this season. The season although relatively quiet has not been benign due to the devastation caused in northern Tonga by 'Waka' early in January. The usual period of peak tropical cyclone occurrence for the Southwest Pacific continues, with an average of two tropical cyclones in February and two in March for the whole region, in seasons similar to the present. On average, the highest frequencies have occurred over the Coral Sea east to Fiji, including Vanuatu and New Caledonia. The March issue of the ICU will provide an update on tropical cyclone information.
The Southwest Pacific Climate in 2001
By Stuart Burgess and Dr Jim Salinger, NIWA
The year 2001 was one of contrasts across the Southwest Pacific. Important drivers of the annual pattern were the fading of La Niña to neutral ENSO conditions, the strength of the trade winds and the distribution of warm and cool SST anomalies.
The Southwest Pacific tropical cyclone season of 2000/01 was the least active since that of 1994/95. It had the latest start for any season in at least 30 years. There were only five cyclones overall, with four occurring in just a few weeks between 20 February and 5 March. Fortunately none resulted in severe damage or loss of life.
A noticeable shift from below to above average SSTs occurred from June onwards over Kiribati, with a return to neutral ENSO conditions. Mean air temperatures were 0.3 to 0.5°C above normal for the year in New Caledonia, Fiji, Tuvalu, Tonga, and parts of Vanuatu, and near average elsewhere.
The La Niña impact on rainfall distribution was evident in the annual OLR anomaly pattern (see figure), even after a return to neutral ENSO conditions, as enhanced trade winds east of the dateline kept the SPCZ further south and west than usual for much of the year.
Below average rainfall was recorded in the central equatorial region (Western and central Kiribati, Tuvalu, Tokelau, and the Northern Cooks), where the first half of the year was very dry. SSTs were below average in the areas where below average rainfall occurred. Annual rainfall was less than 75% of average in some of these areas. Rainfall was also below average in the southwest Coral Sea and along the Queensland coast of Australia.
Areas of enhanced rainfall and below average outgoing longwave radiation occurred in the west, from Papua New Guinea to Tonga including the Solomons, and parts of Vanuatu and Fiji, with totals exceeding120% of average on some islands. SSTs were above average in these areas. Rainfall was also above average over northern New Zealand.
Outgoing long-wave radiation and rainfall anomalies for 2001
Outgoing Long-wave Radiation (OLR) anomalies, in Wm-2 are represented by hatched areas, and rainfall percentage of average, shown by numbers. High radiation levels (yellow) are typically associated with clearer skies and lower rainfall, while cloudy conditions lower the OLR (blue) and typically mean higher rainfalls.