Details
Sea-surface temperature data for January 2005 show positive anomalies across much of the equatorial Pacific, including a region where anomalies exceed +1°C between 160°E and 160°W. However smaller patches of positive anomalies in this range evident further east during December dissipated during January, with a weak cooling trend observed during the month. Weak negative anomalies along the coast of Ecuador reappeared during January, while in the far west, small patches of weak anomalies emerged near Papua New Guinea. In general, there was a weak cooling across the tropical Pacific during January with the strongest cooling occurring in the eastern parts.
The latest weekly data show that during the past fortnight, all five indices fell by approximately 0.1 to 0.2°C, in response to enhanced Trade Winds across the tropical Pacific. The one exception was NINO2 that fell by almost 0.6°C to a value of –0.37°C. NINOs 3.4 and 4 remain near El Niño thresholds, at +0.55 and +0.93°C, respectively. Most indices have shown a downward trend now for several weeks, some since November 2004.
The 7-day SST anomaly map shows patches of positive anomalies ranging from +1 to +2°C in the central and western Pacific, with a large area spanning south of the equator around the dateline. The area along the equator recording anomalies in the +1 to +2°C range has steadily contracted since the beginning of the year, while weak negative anomalies have also developed in the far eastern Pacific and along the South American coast during the past week. This cooling trend observed across the tropical Pacific has resulted from enhanced Trade Winds recorded across much of the tropical Pacific, particularly near the dateline.
Subsurface data for January show that positive anomalies across much of the Pacific between the surface and the thermocline (approximately 100 m depth) continue to weaken. The highest anomalies are in the central Pacific where they just exceed 2°C above average. Negative anomalies have intensified in the vicinity of the thermocline across almost the entire Pacific, suggesting the thermocline is currently shallower than usual (the thermocline usually deepens during an El Niño phase). Temperatures dropped more than 2.5°C below average just west of the dateline, and around 2°C below average in the eastern Pacific. This cooling trend, observed across the Pacific in both the surface and subsurface resulted from enhanced Trade Winds prompting upwelling along the equator. The TOGA TAO subsurface data for the 5 days ending 31st January show positive anomalies across much of the tropical Pacific, mostly in the layer above the thermocline, with negative anomalies at greater depths. The highest anomalies, approaching +3°C are situated on the thermocline near 175°W.
An archive of past SST and sub-surface temperature charts is available.
In terms of the developments in the atmosphere, the Southern Oscillation Index (SOI) for January was the first positive value for seven months. A slightly above average monthly MSLP value in Tahiti and near average in Darwin produced a January SOI of +2, rising 10 points from the December value of –8 (see SOI graph, SOI table).
During El Niño episodes, there is a sustained weakening of the Trade Winds across much of the tropical Pacific but a return to near-average values as El Niño decays. During January, Trade Winds were stronger than average across much of the Pacific, particularly around the dateline. Weak westerly anomalies were recorded in the central to eastern Pacific for a brief period towards the end of the month, but had minimal impact on ocean temperatures. This period of enhanced Trade Winds that began towards the end of December (earlier in the far western Pacific) has caused a cooling trend in both surface and subsurface waters in the tropical Pacific. The surface wind pattern in recent months is characteristic of neutral ENSO conditions. The TAO/TRITON map (small image above), for the five days ending 31st January, shows that the Trade Winds have been stronger than average in the central and eastern Pacific, but weaker than normal west of the dateline.
Cloudiness near the dateline in the central Pacific is another important indicator of El Niño, as it normally increases during these episodes with a return to near-average values during the decay phase. Since May, cloud amounts have oscillated around the climatological mean, with short periods of both below and above average cloudiness around the dateline. This pattern continued during January, with enhanced convection being recorded in the first and last weeks and suppressed convection in the middle weeks.
Over the past six months a pattern of suppressed convection over the Maritime Continent and increased cloud just west of the dateline is similar to what occurs during an El Niño event. However, the recent pattern is displaced further west than in a typical El Niño scenario and recent cloud amounts near the dateline have been near average. Below average cloud amounts over the central to eastern Pacific are also not indicative of a warm (El Niño) pattern.
In the latest survey of international computer models, an 8 to 4 majority favoured neutral temperature patterns in June 2005. By September 2005, only 3 of 8 available models predict the development of warm (El Niño) conditions. Most models indicate central Pacific temperatures to remain on the warm side of average over the next 5 to 8 months, which, even without the occurrence of a clearly define El Niño may impact on Australian climate patterns. The current risk assessment for El Niño conditions developing this year is roughly the same as what would normally be expected early in the year. However March to June is known as the "predictability" barrier and model skill is at its lowest predicting across this span of months.
In Brief
Sea surface temperatures across much of the tropical Pacific have cooled since the beginning of the year, particularly in the eastern Pacific, indicating a return to a neutral (as opposed to borderline warm-neutral) ENSO pattern.
Subsurface data for January shows that there has been a general cooling across the basin since December.
The SOI for January was +2, the first positive monthly value since May 2004.
Trade Winds in the tropical Pacific were mostly near, to above average during January.
Cloudiness around the dateline continues to fluctuate about the long-term average.
Eight of twelve computer models predict neutral eastern Pacific conditions in June 2005.
If it is no already on a full neutral stage it is very close to do so as maybe there still is a very weak el nino but in a phasing out stage.But let's see what CPC=Climate Prediction Center) in their update next week say.But surely the grafic above shows west of SouthAmerica it is cooling at el nino 1-2 and el nino 3 is not warmer than 2 months ago.Only el nino 3-4 and 4 the warmest anomalies are found but they are nothing more than +1.0c.
