Sub-seasonal prediction of the extreme weather conditions associated with the northeastern Australia floods in February 2019

• DOI: 10.5194/egusphere-egu2020-2785
• Publication Date: 2020-03-09T14:34:22Z
• Authors: Tim Cowan; Matthew Wheeler; Morwenna Griffiths; Catherine de Burg...; Matthew Hawcroft
• Keywords: Anticyclone; Coastal flood

<p>In late January to early February 2019, wide-spread flooding, strong winds and relatively cold temperatures over the north-eastern Australian state of Queensland led loss an estimated 625,000 cattle 48,000 sheep. The system that caused these impacts was a quasi-stationary monsoon depression lasted close 10 days, bringing weekly rainfall totals above 1000 mm in some locations, maximum 8–12°C below average, sustained wind speeds 30-40 km/h. same weather event inundation damage more than 3000 homes eastern coastal city Townsville with insurance cost $1.2 billion AUD (https://www.afr.com/companies/financial-services/insurers-reveal-townsville-flood-cost-warn-region-is-unprofitable-20190804-p52do5). Observations reanalysis confirm active Madden-Julian Oscillation pulse stalled western Pacific during period flooding. To south, blocking anticyclone northern Tasman Sea promoted onshore easterly flow, it, low apparent (Cowan et al. 2019).</p><p>In days before event, Bureau Meteorology issued monthly outlook for which provided little indication upcoming extreme event. At time there 50% chance El Niño developing boreal spring, meaning tendency towards warmer drier conditions across northeast. Here we show forecasts from Bureau's newly developed dynamical subseasonal-to-seasonal (S2S) prediction – Community Climate Earth-System Simulator Seasonal version 1 (ACCESS-S1) weekly-averaged were skilful. ACCESS-S1 99-member ensemble forecast doubling probability week prior floods, along increased probabilities extremely high winds. Ensemble-mean amounts, however, considerably underestimated by ACCESS-S1, even initialised at start peak flooding week. This is consistent other state-of-the-art S2S systems. Yet one individual member managed 85% magnitude most heavily impacted region northwest 2 forecast. suggests current systems like are capable getting predicting record-breaking events least week's lead-time. It also appears accurate beyond two weeks (i.e., 3 forecast) floods difficult achieve.</p><p>Reference:</p><p>Cowan (2019): Forecasting rainfall, temperatures, associated Weather Extremes, <strong>26</strong>, 100232, https://doi.org/10.1016/j.wace.2019.100232.</p>