Current state of the Pacific and Indian Ocean
Tropical Pacific Ocean remains ENSO-neutral
Issued on 17 February 2015 | Product Code IDCKGEWW00
Sea surface temperatures across the tropical Pacific Ocean are neutral, having eased away from near El Niño levels over the past two months. However several models suggest some renewed warming may occur beyond May.
The majority of El Niño–Southern Oscillation (ENSO) indicators are currently within neutral bounds. Including temperatures at and beneath the surface of the eastern tropical Pacific Ocean; cloudiness near the Date Line; trade wind strength; and tropical rainfall patterns. In contrast, the Southern Oscillation Index (SOI) is negative, though predominantly due to regional tropical weather patterns rather than broadscale shifts in pressure. It is likely the SOI will rise again in the coming week. It is typical for ENSO events to decay during the late summer to early autumn period, consistent with the recent shift away from near El Niño conditions.
Model outlooks made in the first quarter of the year tend to be less reliable than those made at other times. That said, all international models surveyed by the Bureau indicate tropical Pacific sea surface temperatures are likely to remain warm, but within the neutral range, until at least May. Beyond that time, outlooks favour warm-neutral or El Niño-like ocean temperatures.
Next update expected on 3 March 2015 | print version
- Weekly sea surface temperatures
The SST anomaly map for the week ending 15 February shows warm anomalies persist in the western-central tropical Pacific, with near normal ocean temperature observed across the eastern equatorial Pacific Ocean and in the Coral Sea. Anomalously warm ocean temperatures are observed in the eastern Indian Ocean. When compared with two weeks ago, the ocean has cooled slightly in the far west equatorial Pacific Ocean and Coral Sea and warmed in the Indian Ocean to the northwest of Australia.
- Monthly sea surface temperatures
The SST anomaly map for January shows warmer than average waters covering much of the western tropical Pacific Ocean. Warm anomalies also cover much of the northeast of the Pacific Basin and waters off Australia's east coast. Compared to December, the ocean has cooled across most of the central and eastern equatorial Pacific, particularly east of about 160°W where anomalies were generally near zero for January.
Baseline period 1961–1990. Index December January Temperature change NINO3 +0.8 +0.3 0.5 °C cooler NINO3.4 +0.8 +0.5 0.3 °C cooler NINO4 +1.0 +0.9 0.1 °C cooler
- 5-day sub-surface temperatures
The sub-surface temperature map for the 5 days ending 15 February shows temperatures are near average across most of the sub-surface of the equatorial Pacific, although a small area of weak warm anomalies are present just east of the Date Line at a depth of around 150 m.
- Monthly sub-surface temperatures
The four-month sequence of sub-surface temperature anomalies (to January) shows that a gradual cooling has occurred in the subsurface of the central and eastern equatorial Pacific Ocean over recent months. Water in much of the top 200 m of the eastern half of the equatorial sub-surface was cooler than average during the month of January, with anomalies reaching more than −3 °C in some areas. Weak warm anomalies are present in the top 100 m of the equatorial sub-surface around and west of the Date Line, and also below about 200 m in the same region.
- Southern Oscillation Index
The Southern Oscillation Index (SOI) has persisted around the threshold of neutral and El Niño values over the past fortnight with the latest 30-day SOI value to 15 February −9.5. The recent dip in values of the SOI is predominantly due to regional tropical weather patterns rather than broadscale shifts in pressure. It is common for tropical weather systems to cause transient fluctuations in the SOI during the first quarter of the year, especially if a tropical low or cyclone was to pass near either Darwin or Tahiti.
Sustained positive values of the SOI above +8 may indicate La Niña, while sustained negative values below −8 may indicate El Niño. Values of between about +8 and −8 generally indicate neutral conditions.
- Trade winds
Trade winds were generally near average over the tropical Pacific around and west of the Date Line, though tending weaker than average in some parts of the far western tropical Pacific during the 5 days ending 15 February (see map). Westerly wind anomalies in parts of the western tropical Pacific sometimes occur as a normal part of the breakdown of an El Niño. Over the remainder of the central and eastern tropical Pacific trade winds were near average.
During La Niña there is a sustained strengthening of the trade winds across much of the tropical Pacific, while during El Niño there is a sustained weakening of the trade winds.
- Cloudiness near the Date Line
Cloudiness near the Date Line has fluctuated between near normal and below average in recent weeks.
Cloudiness along the equator, near the Date Line, is an important indicator of ENSO conditions, as it typically increases (negative OLR anomalies) near and to the east of the Date Line during El Niño and decreases (positive OLR anomalies) during La Niña.
- Model outlooks
Most of the surveyed climate models forecast tropical Pacific Ocean sea surface temperatures to be above average, but remaining within the neutral range until at least May. By July, however, six of the eight models suggest a renewed warming, with the NINO3.4 index likely to reach El Niño thresholds. Forecasts spanning February to May (the traditional ENSO transition period) generally have lower accuracy than forecasts made at other times of year, therefore these forecasts should be treated with caution.
- Indian Ocean Dipole
The latest weekly value of the Indian Ocean Dipole (IOD) index to 8 February is −0.4 °C. Climate models surveyed in the model outlooks indicate a continuation of a neutral phase of the IOD in the coming months.
The IOD typically has little influence on Australian climate from December to April. During this time of year, establishment of negative or positive IOD patterns is largely inhibited by the development and position of the monsoon trough in the southern hemisphere.