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Issued on 14 August 2018
Little change in the tropical Pacific; El Ni簽o remains possible in 2018
The El Niño–Southern Oscillation (ENSO) is currently neutral. While the tropical Pacific Ocean has cooled in the past month, most international climate models forecast warming to resume in the coming weeks, with El Niño development possible in the southern spring. Therefore, the Bureau's ENSO Outlook remains at El Niño WATCH. El Niño WATCH means there is approximately a 50% chance of El Niño forming in 2018; double the normal chance.
While the surface of the central to eastern tropical Pacific has cooled over the past month, the water below the surface of the western Pacific is warming again. Although atmospheric indicators such as the Southern Oscillation Index (SOI) remain neutral, tropical cyclones to the north of the equator are acting to increase the warmth in the Pacific by suppressing trade winds.
Most international climate models surveyed by the Bureau predict warming of the tropical Pacific is likely to recommence in the coming weeks. Most models suggest El Niño thresholds are likely to be reached by the end of the year, with the majority suggesting these thresholds could be met by mid to late spring.
El Niño during spring typically means below average rainfall in eastern and northern Australia while daytime temperatures are typically above average over southern Australia.
The Indian Ocean Dipole (IOD) is neutral. However, the ocean to the northwest of Australia remains cooler than normal, which is contributing to suppressed rainfall over southern and southeast Australia. Three of six international climate models suggest a short-lived positive IOD event may develop. A positive IOD during spring typically reduces rainfall in central and southern Australia, and can exacerbate any El Niño driven rainfall deficiencies.
The 30-day Southern Oscillation Index (SOI) to 12 August was −2.9, and the 90-day SOI was −1.9. These values are both well within the neutral ENSO range.
Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.
Sea surface temperatures (SSTs) are close to average in the eastern half of the tropical Pacific Ocean, and slightly above average in the western half, consistent with the current neutral state of ENSO. Waters in the central to eastern region have cooled compared to two weeks ago.
The latest values of the key NINO indices in the tropical Pacific for the week ending 12 August are: NINO3 0.0 °C, NINO3.4 +0.2 °C and NINO4 +0.6 °C. NINO3 and NINO3.4 have cooled compared to two weeks ago, while NINO4 has warmed.
Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than −0.8 °C typically indicate La Niña.
Around Australia, SSTs are generally near average, but weak warm SST anomalies exist around the eastern coastline. Cooler waters can be seen to the northwest of Australia, close to the eastern pole of the Indian Ocean Dipole.
Most of the eight surveyed international climate models predict warming of central equatorial Pacific sea surface temperatures (SSTs) is likely to resume over the coming months. Most models suggest El Niño thresholds are likely to be reached by the end of the year, with the majority suggesting these thresholds could be met by mid to late spring.
最近訪問日期: Mon Aug 20 2018 09:38:33 HKT
最近修訂日期: Mon Jul 11 2016