5.4 El Niño 

El Niño conditions have been neutral across the Pacific Ocean during the third quarter of 2017, but a La Niña event is likely to occur in late 2017. Figure 5.10 illustrates the behavior of the standard Southern Oscillation Index (SOI) of the Australian Bureau of Meteorology (BOM) from October 2016 to October 2017. Sustained positive values of the SOI above +7 typically indicate La Niña while sustained negative values below −7 typically indicate El Niño. Values between about +7 and −7 generally indicate neutral conditions. During the current season, SOI increased from -10.4 in June directly to +8.1 in July, then decreased to 3.3 in August; however, it increased again to +6.9 in September and to +9.1 in October. The sustained large positive value indicates a La Niña might be coming. In the coming months, CropWatch will continue to monitor the condition of La Niña.

Figure 5.10. Monthly SOI-BOM time series for October 2016 to October 2017

Source: http://www.bom.gov.au/climate/current/soi2.shtml

As shown in figure 5.11, the sea surface temperature in the so called "Niño 3.4 region" in the central tropical Pacific Ocean, which is sensitive to El Niño events, is 0.5°C cooler than its 1981-2010 average, according to NOAA monitoring. BOM and NOAA agree that this overall cooler condition indicates that a La Niña event might occur in late 2017, but that it might not be so strong. 

Figure 5.11. Sea surface temperature anomalies, October, 2017

Source: https://www.climate.gov/sites/default/files/ENSO-NovEDD-Fig2_SSTA_map_large.jpg