Discussion: The drought condition across Australia worsened significantly during May. The Bureau of Meteorology/Australia soil moisture anomaly analysis for May indicates very much below average soil moisture exists across all but northeast Australia entering the meteorological winter season (Fig. 1). The lowest soil moisture on record is present in parts of southwest Western Australia.
Fig. 1: The Bureau of Meteorology/Australia soil moisture anomaly analysis for May 2018 is indicated.
During May anomalous rainfall observations indicate below to much below normal amount across southwestern and eastern Australia (Fig. 2). The strongest dry anomalies were on the southwest coast of Western Australia and throughout the east coast of the continent.
Fig. 2: The Bureau of Meteorology/Australia rainfall anomaly analysis for May 2018 is indicated.
Will the drought worsen? Previously, forecasts of a negative phase Indian Ocean Dipole while weak La Nina lingered offered hope of wetter than normal climate during the winter season for parts of the continent easing drought in many areas. However, recent trends indicate the IOD pattern is neutral and El Nino southern oscillation (ENSO) is heading toward El Nino.
The concern is the increasingly impressive warming in the central and eastern subsurface equatorial Pacific Ocean (Fig. 3). The warming is advancing eastward about to reach the northwest coast of South America. The amount of warming indicated, the warmer trend and the eastern shift of the warmth strongly indicates El Nino will form during the next 1-3 months.
Fig. 3: The NOAA/CPC analysis of subsurface temperature anomalies in the equatorial Pacific Ocean indicates strong warming shifting east across the Pacific.
The last 4 El Nino episodes to develop following neutral ENSO or weak La Nina during the second half of the year occurred in 2009, 2006, 2004 and 2002. On average the second half of each analog year was very dry across eastern Australia (Fig. 4). Similar conditions are likely for the second half of 2018 causing a robust drought to worsen.
Fig. 4: The past 4 years when early year observed neutral or cool ENSO transitioning into El Nino the second half of the year and their precipitation anomalies (for JUL-DEC).