News
BAMOS April 2021
7
Special Climate Statement
Extreme rainfall and flooding in eastern and central Australia in March 2021
Bureau of Meteorology
The Bureau ' s Special Climate Statements provide a detailed summary of significant weather and climate events . They are produced on an occasional basis for weather / climate events which are unusual in the context of the climatology of the affected region . Their purpose is to document major events . In doing so , they serve as a historical record , inform the public on the broader historical and climatological context for events , and give easy access to data and information which is in high demand from the media and the public .
Overview of the event
A major rain event affected significant areas of Australia in the second half of March 2021 . The highest rainfall totals occurred in eastern New South Wales , with almost the whole coastline and adjacent ranges receiving significant falls . Extensive heavy rainfall also occurred over large areas of the inland , particularly much of inland New South Wales and northern South Australia . Many catchments on the east coast experienced significant flooding , as did numerous inland rivers , especially in northern New South Wales and southern Queensland .
Moist easterly flow became established over coastal New South Wales on 17 March , associated with a strong , slow-moving high pressure system in the southern Tasman Sea between Tasmania and New Zealand .
This onshore flow persisted for nearly a week . Troughs formed near the coast from time to time , and a small low pressure system moved slowly south along the New South Wales coast on 19 and 20 March , reinforcing the easterly flow on its southern side . The low did not reach the intensity required to be formally classified as an East Coast Low . Some of the heaviest rain occurred during these two days .
Meanwhile , a separate area of low pressure formed over central Australia on 22 March , with a trough and associated north-west cloud band extending from the Kimberley in north Western Australia to the far south-west of Queensland . This occurred in spite of a relatively inactive monsoon and the Madden –
Julian Oscillation being well outside the Australian region . This consolidated over the following 24 hours into a low pressure system over inland areas of southern Queensland and northern New South Wales , which also reinforced north-easterly flow over south-eastern New South Wales . The low then moved south over inland New South Wales , reaching eastern Bass Strait early on 24 March . It continued to move slowly southwards , on a track just east of Tasmania , over the following 24 hours , before accelerating and leaving the Australian region later on 25 March .
Significant rain began along parts of the New South Wales coast on 17 and 18 March , with heavy falls in the Port Stephens area on 18 March . There was also significant thunderstorm activity in northern inland New South Wales and central Queensland during this period , with locally heavy falls . These are not considered as part of this event and are out of scope for this statement . The heaviest rain began on 19 March , focused on the Mid North Coast region , with significant falls covering much of the coast from the Illawarra northwards . Heavy falls extended south to the Sydney region on 21 and 22 March , and northwards to south-east Queensland on 22 and 23 March . The South Coast received regular rain during this period but had its heaviest falls on 24 March as a low approached it from inland . Eastern Victoria also received significant rain on 24 March , while in eastern Tasmania the heaviest rain was on 25 March as the low passed nearby . By 25 March rain had largely cleared from New South Wales , except for isolated , locally severe thunderstorm activity on parts of the South Coast that afternoon .
Widespread inland rain began on 21 March with significant falls in the Kimberley and the western Northern Territory . The heaviest rain shifted to central Australia on 22 March , with extensive falls in northern South Australia and the southern Northern Territory . As this rain area continued to move east , 23 March was a very wet day for most of inland New South Wales apart from the far south-west . The heaviest falls were in the far north of New South Wales , with significant rain also extending to border areas of Queensland . This area of rain cleared to eastern New South Wales on 24 March .