Kimba Wong, Evan Jensen and Natasha Hinrichsen, Bureau of Meteorology( DSS _ HPR _ East _ NSWACT _ Mgr @ bom. gov. au)

River rising over road at Taree. Credit: Yucalyptus / CC0

In May 2025, widespread flooding occurred across parts of New South Wales, particularly in the Hunter and Mid North Coast regions.

The floods claimed four lives, damaged homes, disrupted transport supply chains, and significantly impacted agriculture.

At the heart of this event was a slow-moving east coast trough that drew in tropical moisture, triggering prolonged heavy rainfall over several days.

Here, we take a closer look at this weather system and discuss how such events may evolve in the future.

The trough formation

On 19 May, the trough developed along the New South Wales coast and remained quasi-stationary over the eastern part of the state for four days due to the presence of a blocking highpressure system near New Zealand.

The trough continuously drew in moist easterly winds off the Tasman Sea and further interacted with cooler upper-level air to produce heavy, sustained rainfall.

On 22 May, a low-pressure system developed within the trough, which then moved south on 23 May, causing the rain to shift to the Illawarra, South Coast, and Southern and Central Tablelands before clearing offshore( Figure 1).

Record-breaking rainfall

Large areas of the Hunter and Mid North Coast districts recorded weekly rainfall totals exceeding 200 mm. Cumulative rainfall totals for 19 to 23 May 2025 exceeded 500 mm for some sites( Figure 2).

Eight rain gauge sites across the Hunter and Mid North Coast broke their annual daily rainfall records on 20 May 2025, with three of those sites breaking these records again the following day.

The extreme rainfall overwhelmed catchments already affected by a wetter-than-average autumn, with eastern catchments, particularly in the Hunter and Mid North Coast, experiencing widespread flooding. Record flood levels were observed along the Manning River, particularly at Taree, where river levels reached approximately 6.32 metres, surpassing the March 1929 record by 0.35 metres. Major flooding also occurred along the