September 2026 Long Range Forecast

Introduction This long range weather forecast outlines the expected evolution of major weather patterns across Australia during September 2026. The focus of this outlook is on identifying rainfall phases, temperature tendencies, key risk windows and structural pattern transitions rather than short term or daily detail. September represents a transitional month as Australia moves from late winter frontal dominance toward early spring instability and thunderstorm driven rainfall. Outcomes this month are expected to be corridor based and event dependent rather than uniformly wet or dry nationwide. Seasonal and climatological positioning September sits within the winter to spring transition phase. Climatologically, this period is characterised by: - Gradually declining winter frontal rainfall across southwest WA - Progressive frontal passages across southern Australia - Increasing northwest heat transport ahead of mid latitude systems - Emerging thunderstorm corridors across SA, VIC, NSW and QLD - Limited sustained tropical moisture influence across the north and northeast Rainfall during September typically becomes increasingly dependent on the timing and structure of individual systems rather than persistent broad wet phases. Typical conditions reference Under average September conditions: - Southwest WA remains exposed to frontal systems but rainfall efficiency declines compared to winter - Southern SA and VIC experience intermittent fronts and windy conditions - Inland Australia begins warming under strengthening northwest flow - Storm activity increases across eastern and southeastern districts - The NT and northeast QLD remain largely pre wet season, with rainfall sporadic and instability driven This provides the baseline reference for forecast departures.

Climate context Large scale climate guidance provides background context only and does not determine individual events. Long range anomaly guidance for September 2026 broadly suggests: - A tendency toward below average rainfall for southwest WA and parts of the southern coastal belt - Near average conditions across much of southern Australia - Near to locally above average potential across eastern VIC and eastern NSW where storm corridors activate - A weak positive signal across parts of the northwest and central interior - Mostly neutral conditions across the northeast These signals are interpreted in alignment with the forecast sequencing below and seasonal behaviour. Key drivers and pattern setup September 2026 is driven by a structured progression: - A late August primary wet window spilling into early September - A high pressure dominated reset phase with wind as the primary feature - Rebuilding frontal and low pressure activity mid month - Late month upper trough amplification potential with northwest cloudband influence Rainfall distribution this month is expected to be delivered through defined windows rather than continuous activity. Forecast overview Overall rainfall distribution for September 2026 favours: - Below average rainfall across southwest WA - Near to slightly below average rainfall across parts of the southern coastal belt of SA and southern VIC where frontal rainfall may be progressive - Near average rainfall overall across much of southern Australia - Near to locally above average rainfall across eastern VIC, eastern NSW and southeast QLD within storm corridors - Near average to slightly above average rainfall across parts of the northwest and central interior, conditional on late month cloudband development - Near average rainfall across northeast QLD - Near average to slightly above average rainfall across central and eastern NT where upper trough interaction late month may promote scattered storm development - Near average rainfall across the eastern interior of QLD and NSW overall, with outcomes dependent on storm alignment rather than persistent moisture Temperature tendencies: - Near to below average during frontal passages and southern wind phases - Above average inland during northwest flow periods, particularly across WA, SA, NT and western QLD - Increasingly warm across the central and eastern interior late month ahead of the major cycle - Moderated temperatures along the east coast during southeast wind phases