Monthly climate
Climate developments in June 2008
Outgoing Long-wave Radiation anomalies for June 2008. (Click for enlargement and detail)
The South Pacific Convergence Zone (SPCZ) extended southeast from Papua New Guinea to Fiji and Niue and across to the Southern Cook Islands and Austral Islands, with an overall displaced position southwest of normal. A region of suppressed convection that was persistent along the Equator during the austral spring and summer has contracted, but still extends from Western Kiribati to Eastern Kiribati including Tuvalu, Tokelau, and the Northern Cook Islands. An area of suppressed convection emerged to the southwest of the SPCZ and encapsulated New Caledonia for a majority the month.
Rainfall was well above average in most of Fiji, Samoa, Tonga, and northern Vanuatu due to a southwest-displaced SPCZ. New high monthly rainfall totals were recorded at Faleolo and Apia, Samoa, with 242 mm and 470 mm (260% and 353% of normal, respectively), as well as at Lakeba, Fiji, with a record high of 574 mm (736% of normal). Many stations in Fiji had high monthly rainfall totals ranging from 150 – 250% of normal, with more than 100 mm falling in a 24-hour period at several locations from 11 - 16 June. Heavy sustained rainfall also caused flooding in Samoa on 7 June and 15 June.
New Caledonia was located outside of the SPCZ during June, and experienced record monthly low rainfall at many locations and a global station mean of –21% of normal precipitation. Record low rainfall was also recorded at Norfolk Island (30 mm, 20% of normal), and near-record low rainfall also occurred at Townsville, Australia (0.8 mm). A near-record monthly low rainfall total was also recorded at Penrhyn in the Northern Cook Islands (22 mm) and in southern Vanuatu at Aneityum (83 mm).
Near or below normal rainfall fell over much of French Polynesia and Tuamotu, which have received below average precipitation for much of the past year. French Polynesia reports a 20% rainfall deficit overall, and dry conditions in the Marquesas and the Tuamotu Archipelago, with only Tahiti receiving near-normal rainfall for the month.
| Country | Location | Rainfall (mm) | % of average | Comments |
|---|---|---|---|---|
| Samoa | Faleolo | 242 | 260 | Record high |
| Samoa | Apia | 470 | 353 | Record high |
| Fiji | Lakeba | 574 | 736 | Record high |
| Fiji | Vunisea | 421 | 334 | Record high |
| New Caledonia | Koumac | 3 | 5 | Record low |
| Cook Islands | Penrhyn | 22 | 15 | Near-record low |
Soil moisture in June 2008
Estimated soil moisture conditions at the end of June 2008, 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, but 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.
French Polynesia reports there are still important soil moisture deficits in the Tuamotu and Marquesas Islands. Nadi (Fiji) projects dry soil moisture conditions which is in contrast to many other stations that received high rainfall in June. Soils continued to be moist (at field capacity) for the time of year at Port Vila (Vanuatu) and Hanan Airport (Niue).
El Niño/Southern Oscillation (ENSO)
Sea surface temperature anomalies (°C) for June 2008. (Click for enlargement)
Mean sea surface temperatures (°C) for June 2008. (Click for enlargement)
During June, La Niña conditions continued to weaken in the equatorial Pacific. Overall the tropical Pacific temperatures are close to neutral, although some remnants of La Niña persist east of the Date Line. A warm water tongue off the coast of Ecuador has strenghtened since last month.
Across the equatorial Pacific, ocean surface temperature anomalies have continued to ease from previous months. The NINO3 anomaly increased during June to +0.5 °C (3-month mean +0.2 °C), and is a continuation of the progressive warming from –1.5 °C in February 2008. NINO4 remains below normal at –0.5 °C in June (3-month mean around –0.7 °C), but this negative anomaly continues to weaken at the surface does not extend below 100 m. A positive sub-surface temperature anomaly persists west of the Date Line and is weakening, and the positive anomaly has intensified near South America above 100 m.
The near-Equatorial trade winds are slightly enhanced in the central equatorial Pacific and near normal elsewhere. Convection was largely suppressed along the equatorial regions from the eastern Pacific through to Indonesia. The SPCZ was active from near Fiji towards the Southern Cook Islands. The Southern Oscillation Index (SOI), also shifted to a slightly positive value in June, and is +0.4 (3-month mean +0.1). The TRMM ENSO precipitation index was around –1.2 at the end of June (weakening from a strong La Niña value of –2 in April). The Madden - Julien Oscillation is very weak at present.
OLR anomalies show a coherent but weak region of suppressed convection extending from 170 °E across the date line toward the Northern Cook and Marquesas Islands. The area of relatively enhanced convection last month along the SPCZ is more consolidated in a narrow band across Fiji, Niue, and Tonga. In the past month the region to the east of the Date Line around the equator had the most visible OLR changes. Overall, the SPCZ is still displaced to the southwest of its normal position.
All dynamic and statistical climate models bar one (NASA-NSIPP) indicate ENSO neutral conditions during July–September, and continuing neutral through to March 2009. The NCEP discussion of 5 June indicates a transition from La Niña to ENSO-neutral conditions during June–July. The IRI summary of 18 June gives a 75% chance of a return to ENSO-neutral conditions in the June to August period, and the probability of returning to La Niña only 15%. The Australian weekly tropical summary of 27 May suggests ENSO-neutral conditions nowexist, and will persist through the austral spring.
Forecast validation: April to June 2008
A La Niña-like pattern was expected, with a large region of suppressed convection forecast along the equatorial Pacific from Western to Eastern Kiribati, including the Solomon Islands, Tuvalu, the Northern Cook Islands, the Tuamotu archipelago, the Marquesas, and the Society Islands. Average rainfall was forecast for Papua New Guinea, Samoa, the Southern Cook Islands, and Pitcairn Island. Enhanced convection was forecast from Vanuatu through to the AustralIslands of French Polynesia, including New Caledonia, Fiji, Tonga, and Niue, with above average rainfall expected.
The rainfall outlook for the April – June 2008 period was very similar to what was forecast, the ‘hit’ rate being 69%, 15% higher than average. Rainfall totals were underestimated slightly for the northern fringe of French Polynesia, and higher than anticipated rainfall occurred in Samoa.