The 2015 El Niño is now well-established and continues to strengthen, Australian Bureau of Meteorology (BOM) reports today. International climate models surveyed by the BOM all indicate that El Niño will continue to strengthen, and persist into early 2016.

In the coming weeks, the central tropical Pacific Ocean (the NINO3.4 region) may exceed the peak values reached during the 2002 and 2009 El Niño events, but current anomalies remain well short of the 1982 and 1997 peaks, it said and added that peak values are normally recorded late in the year.

Trade winds remain weakened and are likely to contribute to more warming of the tropical Pacific Ocean. Other indicators such as cloudiness near the Date Line, the Southern Oscillation Index, and sub-surface temperatures in the tropical Pacific Ocean remain typical of an established El Niño.

Index Previous Current Temperature change

(2 weeks) NINO3 +2.0 +1.9 0.1 °C cooler NINO3.4 +1.6 +1.7 0.1 °C warmer NINO4 +1.2 +1.0 0.2 °C cooler

Baseline period 1961–1990. Image credit: BOM.

Over the past fortnight, sea surface temperature (SST) anomalies have decreased slightly in the eastern equatorial Pacific. Warm anomalies persist along the equator from the South American coastline to about 160°E. Anomalies for the week ending August 2 exceeded +2 °C across nearly all of the eastern equatorial Pacific and smaller areas of the central Pacific.

All five NINO indices again exceeded +1 °C this week.

Warm anomalies are present across most of the northern half of the Pacific basin, except for parts of the northwest. The eastern half of the northern Pacific is more than one degree warmer than average, and two degrees warmer than average in places. Warm anomalies are also present along parts of the east coast of Australia, in areas to Australia's west, and across much of the Indian Ocean.

The SST anomaly map for July 2015 shows positive anomalies extended from the South American coastline, across the equatorial Pacific, past the Date Line to around 160°E. Compared to June, the strength of these anomalies have increased in the eastern Pacific. Strong warm anomalies also persisted across much of the northeast of the Pacific Basin, with weak warm anomalies to Australia's east, and moderate to strong warm anomalies across much of the Indian Ocean.

NINO3 measured its warmest monthly anomaly since the 1997–98 El Niño, with an anomaly of +1.9 °C for July 2015, ahead of +1.7 °C in June 2015 and +1.6 °C December 2009. The July 2015 value of NINO3.4 was +1.5 °C.

In the coming weeks, the NINO3.4 region may exceed the peak anomaly values reached during the 2002 (+1.6 °C) and 2009 (+1.7 °C) El Niño. The current El Niño has already exceeded the 2006 peak of +1.2 °C, but current anomalies still remain well short of the 1982 and 1997 peaks (+2.8 °C and +2.7 °C respectively).

Index June July Temperature change NINO3 +1.6 +1.9 0.3 °C warmer NINO3.4 +1.3 +1.5 0.2 °C warmer NINO4 +1.1 +1.1 no change

Baseline period 1961–1990. Image credit: BOM.

The sub-surface temperature map for the 5 days ending August 2 shows temperatures are warmer than average in the top 100 m of the central to eastern equatorial Pacific and cooler than average below the surface of the ocean in the western equatorial Pacific. Water in far eastern Pacific sub-surface is very much warmer than average, with anomalies around 75 m depth reaching more than 6 °C warmer than average. Warm anomalies in the east-central Pacific are somewhat stronger than they were two weeks ago.

Cool anomalies in the western equatorial Pacific remain similar to what they were two weeks ago, with a broad area more than 2 °C cooler than average between around 100 m and 200 m depth.

The Southern Oscillation Index (SOI) has risen somewhat over the past two weeks, but remains firmly within negative values. The 30-day SOI value to August 2 was −14.4.

Trade winds for the 5 days ending 2 August show westerly anomalies were present over the western half of the equatorial Pacific. Trade winds were reversed (i.e. westerly winds) to the west of the Date Line.

Trade winds have been consistently weaker than average, and on occasion reversed in direction (i.e. westerly rather than easterly), since the start of 2015.

Cloudiness near the Date Line was above average during the second half of July and early August.

Cloudiness along the equator, near the Date Line, is an important indicator of ENSO, 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.

All eight of the surveyed international climate models indicate the central Pacific Ocean will warm further during the coming months. All surveyed models indicate that NINO3.4 will remain above El Niño thresholds until at least the end of 2015.

Source: BOM

Featured image: Super Typhoon "Soudelor" on August 4, 2015. Image credit: NASA Aqua/MODIS.