Climate developments in June 2007
Outgoing Long-wave Radiation anomalies for June 2007. (Click for enlargement and detail)
The South Pacific Convergence Zone (SPCZ) extended from southern Papua New Guinea east towards Tuvalu and the Date Line, with little activity east of the Date Line. Convergence was substantially enhanced over the north and east of Australia, extending southeast across the Tasman Sea to the region south of New Caledonia due to the development of at least three significant depressions off the eastern Australia seaboard during the month. Another region of enhanced convergence affected the Southern Cook Islands and the Austral Islands. An elongated region of suppressed convection occurred along the equator from northern Papua New Guinea, across the Date Line, and east to South America. Another region of suppressed convection existed over Fiji, extending towards Vanuatu and Tonga.
Rainfall was at least 125% of normal in parts of Southern French Polynesia. High rainfall totalling 225 mm within 24 hours occurred at Koumac, in New Caledonia, towards the end of June. This was the wettest June on record over the tropical part of Australia, in more than 100 years of measurement. June rainfall was 50% or less of normal over much of Fiji, and also below normal over much of Western Kiribati, Wallis and Futuna, central and southern Tonga, and parts of northern and central French Polynesia.
June mean air temperatures were above average in most Southwest Pacific islands located between 14° and 25°S. Anomalies were largest in New Caledonia, where temperatures were more than 2.0 °C above average at many locations and it was the warmest June on record for about 60% of recording sites. Temperatures were 1.0 °C or more above average in parts of Vanuatu, Fiji, Niue, the Southern Cook Islands, and southern French Polynesia, and at least 0.5 °C above average in Vanuatu, Tuvalu and Tonga. Several Fijian locations recorded their highest June extreme maximum air temperature on record.
Tropical Southwest Pacific mean sea-level pressures were generally below average in the tropical Southwest Pacific from Papua New Guinea to the region just east of the Date Line, as well as in the Tasman Sea equatorial surface easterlies occurred in 87% of observations at Tarawa, an increase of 20% from that of May.
| Country | Location | Rainfall (mm) | Difference from average(°C) |
|---|---|---|---|
| New Caledonia | Noumea | 23.3 | +2.1 |
| Fiji | Nadi Airport | 25.6 | +1.4 |
| Niue | Hanan Airport | 24.7 | +1.5 |
| Cook Islands | Rarotonga Airport | 24.3 | +1.3 |
| French Polynesia | Rapa | 20.7 | +1.6 |
Soil moisture in June 2007
Estimated soil moisture conditions at the end of June 2007, using monthly rainfall data. (Click for enlargement)
Estimates of soil moisture shown in the map (right) are based on monthly rainfall for one station in each country. Currently there are not many sites in the water balance model. It is planned to include more stations in the future.
The information displayed is based on a simple water balance technique to determine soil moisture levels. Addition of moisture to available water already in the soil comes from rainfall, and losses via evapotranspiration. Monthly rainfall and evapotranspiration are used to determine the soil moisture level and its changes.
Please note that these soil moisture calculations are made at the end of the month. For practical purposes, generalisations were made about the available water capacity of the soils at each site.
At the end of June 2007, Apia and Rarotongan soils were at field capacity while Nadi soils were dry.
El Niño/Southern Oscillation (ENSO)
Sea surface temperature anomalies (°C) for June 2007. (Click for enlargement)
Conditions in the tropical Pacific are currently neutral, although they are suggestive of a slow La Niña development.
The pattern of sea surface temperature (SSTs) anomalies resembles conditions typical of La Niña, with colder than average waters in the far eastern Pacific and slightly warmer than average waters in the western Pacific. SSTs remain slightly above normal to the west of the Date Line, and then below average SSTs extend from 130°W to the South American coast. Surface temperatures have changed only slowly over the past three months.
The NINO3 anomaly was –0.3°C in June (no change from May, and an AMJ average of –0.2), while the NINO4 anomaly was +0.5°C in June (up from +0.3°C in May, and an April–June mean around +0.4°C).
The Southern Oscillation Index (SOI) has risen in the last month to +0.4, and so is now more in phase with the oceanic part of ENSO than in earlier months.
Subsurface data for June shows a slight weakening of the negative anomaly in the top 150 metres between the Date Line and the South American coast. There has been the appearance of a small "warm-blob" at 110°W (and depth of 50 m), probably in response to a prominent westerly wind burst along the Pacific equator during May. However, during June the trade winds picked up and are now stronger than is usual for this time of year.
OLR and tropical rainfall anomalies for June indicate suppressed convection along the equator in the Pacific. The ENSO Precipitation Index of –1.13 (May value was –0.40) indicates a strengthening of a (weak) cold ENSO event. The global sea surface height (SSH) anomaly continues to show a classic La Niña pattern with lower SSH anomalies from the Date Line east, surrounded by a horseshoe of higher SSH anomalies in the western Pacific. The magnitude of SSH in June has slightly decreased since last month. The Madden-Julian Oscillation is presently weak with its centre of activity to the west of the Date Line.
The dynamical models show a transition to La Niña conditions over the next 3 months, with this persisting for the remainder of the year before a return to neutral conditions early in 2008, whilst the statistical models project neutral ENSO states for the next 6–9 months. No model indicates warm conditions during the remainder of the year. Historically, the next few months are a favourable period for La Niña development. The NCEP synopsis suggests a transition from ENSO-neutral to La Niña conditions is possible within the next 1–3 months, while the IRI synthesis gives a probability of 55% for a La Niña by November. The probability of El Niño conditions re-emerging during the forecast period remains at or below 5%.
Forecast validation: April to June 2007
Suppressed convection and below average rainfall was expected over Eastern Kiribati, with near or below average rainfall in Western Kiribati. Enhanced convection with above average rainfall was forecast for the Tuamotu Islands, with near or above average rainfall in the Society, and Marquesas Islands, the Cook Islands, Pitcairn Island, Wallis and Futuna, Tokelau, and Samoa, and also in the Solomon Islands and Vanuatu. Near average rainfall was expected elsewhere in the region.
A region of weakly enhanced convection and above average rainfall extended south from the Samoa to include Tonga (which was wetter than expected), while suppressed convection and below average rainfall occurred in the equatorial region about and east of the Date Line. Rainfall was also below average (and lower than expected) in the Northern Cook Islands, and parts of Central and Southern French Polynesia. The ‘hit’ rate for the April–June 2007 rainfall outlook was about 65%.