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05/09/2023, 5:15 am EDT

Australia Season 1-3 Ahead Outlook: +IOD/El Nino ahead promise an evolving dry bias to Australia climate for the second half of 2023.  

Highlight: +IOD/El Nino ahead promise an evolving dry bias to Australia climate for the second half of 2023.   Executive Summary: The Australia season 1-3 ahead forecast is updated and valid for meteorological winter 2023 through next summer. The primary catalyst to forecast results are an evolving positive phase Indian Ocean dipole and El Nino each forecast to initiate during the next 3-6 weeks. The +IOD/El Nino combination motivates a dry bias to the Australia climate following a period of wet climate due to La Nina of the past several years. Drought evolution for next summer is likely. Climate: A major shift in the ocean system is forecast for the middle third of 2023. The long-standing (2020-23) La Nina episode is fading. Nino34 SSTA is on the El Nino threshold. A transient convection phase of the Madden Julian oscillation (MJO) driven by a westerly wind burst (WWB) across the tropical Pacific should push ENSO into El Nino onset during June. El Nino is forecast to strengthen during the second half of 2023 although intensity forecasts vary (Fig. 1). Meanwhile, waters northeast and east of Australia remain somewhat warmer than normal. The warm waters are associated with a marine heat wave responsible in-part for all kinds of weather extremes from Australia to New Zealand this past summer season. The marine heat wave is semi-permanent and likely to last through 2023 (Fig. 2). In the tropical Indian Ocean, a weak negative phase of the Indian Ocean dipole (-IOD) is present now. However, the Australia Bureau of Meteorology is forecasting a moderate-to-strong +IOD to emerge over the next 1-3 months peaking during Q3/2023 before weakening later this year (Fig. 3). Entering the cold season, Australia soil moisture conditions indicate mostly wet signatures across the western half of the continent with dryness either side of the New South Wales/Queensland border (Fig. 4). The trend into El Nino and +IOD suggests a drier climate ahead for Australia. Fig. 1: A collection of all dynamic and statistical Nino34 SSTA forecasts reveal El Nino ahead with unclear intensity.   Fig. 2: International multi-model ensemble (IMME) global SSTA forecast for September 2023.   Fig. 3: The Australia Bureau of Meteorology projection of the Indian Ocean dipole for 2023.    Fig. 4: The Australia Bureau of Meteorology soil moisture analysis for April 2023.   Forecast methodology: The Australia season 1-3 ahead climate forecast is based on a constructed analog uniquely designed by Climate Impact Company. The constructed analog is primarily a regional SSTA-based analog of past similar conditions and projecting climate forward based on the forecast of those SSTA regimes. JUN/JUL/AUG 2023: During meteorological winter 2023, the prevailing upper air pattern based on the constructed analog forecast, features a persistent weak upper trough over the +IOD-cooled waters west and northwest of Australia, the semi-permanent upper-level ridge east of Australia with core near New Zealand and motivated by the New Zealand marine heat wave, and an amplified upper ridge south-southeast of Australia. The southern annular mode (SAM) often referred to as the Antarctic oscillation (AAO) is in the positive phase as a stronger than normal polar vortex is evident. The sensible weather forecast indicates that on average Southern Australia is cooler than normal for upcoming winter. The positioning of the persistent upper air features implies coldest risk is across the Interior South. Conversely, Northern Australia is not at risk of cooler air masses and a warmer than normal winter season is expected. The precipitation forecast is normally dry with drier than normal signatures on the East and Southeast Australia Coast. A +IOD/El Nino climate should bias the precipitation pattern drier than normal. The outlook is not as cool as the previous forecast. Fig. 5-6: The Climate Impact Company constructed analog temperature and precipitation anomaly climate forecasts for JUN/JUL/AUG 2023.  SEP/OCT/NOV 2023: During meteorological spring 2023, the constructed analog forecast projects a large upper-level high-pressure ridge across ocean waters just south of Australia. The vigorous wintertime Antarctic polar vortex is not as strong. El Nino is intact although the strength of this feature is uncertain. +IOD peak intensity occurs during early spring. The +IOD/El Nino combination biases the Australia climate drier than normal, possibly more so than indicated by the climate forecast. Springtime is also generally warmer than normal across the Interior East and Southeast plus Southwest Australia zones. The forecast is not as warm as the previous outlook. Fig. 7-8: The Climate Impact Company constructed analog temperature and precipitation anomaly climate forecasts for SEP/OCT/NOV 2023.  DEC/JAN/FEB 2023-24: The summer 2023-24 forecast is likely hotter and drier than normal. The risk of developing drought is HIGH! During next summer, a full-tilt El Nino is favored. The +IOD pattern fades, but El Nino could motivate widespread dryness (depending on intensity). The sensible forecast is not as hot as the previous outlook although drier across the northern half of the continent. A weak or failed monsoon is possible. Fig. 9-10: The Climate Impact Company constructed analog temperature and precipitation anomaly climate forecasts for DEC/JAN/FEB 2023-24.