Marine Heatwaves Fueling Historic Australia Rains in 2025

Climate Impact Company Climate Research

Issued: Friday May 23, 2025

Highlight: Marine heat waves fueling historic Australia rains in 2025.

Fig. 1-3: Rainfall amount for May so far and the rainfall anomalies for 2025 so far across Australia plus the 6-month temperature deciles across Australia.

Discussion: Another devastating flood has struck Australia centered on the northern coast of New South Wales where “incessant rain cut off entire towns, swept away livestock and destroyed homes” according to a Reuters report. So far in May, this area has received 600-800 MM (23-31 inches) of rainfall (Fig. 1). The extreme rainfall on the New South Wales Coast is another example of the many flooding rainfall events of 2025 so far across much of Queensland and eastern New South Wales (Fig. 2). While historic rainfall has affected these areas, much of Australia observed extreme heat during the recently ended warm season including the hottest NOV-APR 6-month period on record for most of Southern Australia (Fig. 3). The climate extremes are explained, in a large way, by the ongoing presence of very warm marine heatwaves (MHW) off the Australia West and South Coast and stretching from in between Australia and New Zealand eastward well past the Dateline (Fig. 4). The MHW off the West Coast of Australia developed last October and the MHW east and southeast of Australia intensified dramatically last December. The influence of the anomalous warm ocean also warmed the atmosphere as implied by the titanic upper-level high-pressure ridge southeast of New Zealand (Fig. 5) ridging northwestward into Southern Australia (causing the record heat). Compensating for the immense high-pressure area is persistent low pressure on the Queensland Coast fueling the historic wet climate. The anomalous warm ocean is linked to the warming of the atmosphere and strengthening subtropical high pressure which when extending over a land mass can cause extreme heat. Conversely, MHW’s also increase the amount of low-level atmosphere moisture that when entrained by storms (synoptic scale or tropical cyclones) leads to excessive rainfall and flooding. A large increase in MHW’s during the past decade appears to be a leading contributor to global ocean temperature rise and Australia is a location directly affected by the attendant climate produced by MHW’s.

Fig. 4-5: The 90-day global SSTA analysis identifying marine heatwaves near Australia plus the 500 MB anomalies across Australia and vicinity for 2025 so far.