Climate developments in January 2006
A large area of suppressed convection, characteristic of weak La Niña conditions, continued to affect the central equatorial Pacific extending from Nauru to Eastern Kiribati and the Northern Cook Islands.
The SPCZ was quite active, extending from the Solomon Islands towards the Cook Islands, resulting in above average rainfall over parts of American Samoa and Northern Tonga. Near the Date Line, the SPCZ was located further south than average. In the west it merged with a large and active area of enhanced convection, associated with the monsoon trough, which affected Indonesia, Papua New Guinea, and northern Australia.
Rainfall was at least 125% of average in parts of Fiji, Samoa, southern Tuvalu, and Tonga, as well as parts of New Caledonia. January rainfall was less than 50% of average in the north of Western Kiribati and northern Tuvalu.
In French Polynesia, Tahiti-Faaa recorded 18 days with thunderstorms during the month, their highest on record for January. In Fiji, Rotuma Island recorded 28 days of rain.
Mean air temperatures were at least 1 °C above average in southern Tonga and southern French Polynesia. They were near average in New Caledonia.
Tropical Southwest Pacific mean sea-level pressures tended below average over much of the tropical Pacific within about 10° both north and south of the equator, extending west across Papua New Guinea. This was a marked change from past months when pressures were below average east of the Date Line.
Equatorial surface easterlies were very persistent along the equator, occurring in about 99% of observations at Tarawa.
| Country | Location | Monthly Rainfall (mm) | % of average | Comments |
|---|---|---|---|---|
| Fiji | Rotuma | 954 | 269 | Record high |
| New Caledonia | Ouanaham | 368 | 204 | Well above average |
| New Zealand | Raoul Island | 30 | 23 | Well below average |
Currently, the equatorial Pacific Ocean is showing characteristics of a weak La Niña. This development is unprecedented for this time of the year, and is likely to be short-lived, based on some global diagnostic models.
The region of largest negative sea surface temperature (SST) anomalies migrated from near the South American coast towards the central Pacific in January, associated with enhanced trade winds and suppressed convection centred near the Date Line. Convection is enhanced over northern Australia and Indonesia. The NINO3 SST anomaly rose to about 0.4 °C for January (-0.7 °C in December, -0.5 °C for November-January) and NINO4 fell to -0.3 °C (+0.2 °C in December, +0.1 °C for November-January). A cold subsurface temperature anomaly centred near 140° W strengthened during the month, but remained stationary. The Southern Oscillation Index (SOI) rose above +1 in January, from a neutral value in December (-0.1). The 3-month mean SOI is still in the neutral range. A moderate Madden-Julian Oscillation event moved through the western Pacific during the last week of January.
One in three models show La Niña conditions for February-April, all trending back towards neutral conditions by mid-year. The latest NCEP/CPC statement (9 February) suggests La Niña conditions expected to continue for next 3 to 6 months, while the IRICP summary gives a 50% chance of La Niña in the next few months, reducing to 25% (climatology) by mid-year.
The current conditions continue but may ease by southern hemisphere winter 2006.