From storm to study: Insights on resilience from Tropical Cyclone Alfred

Tropical Cyclone Alfred (TC Alfred) approached south-east Queensland as a category 2 event with gust wind speeds estimated at 155 kilometres per hour. It stalled on approach and caused strong winds for around three days in southeast Queensland and north-east New South Wales (NSW). It also weakened and eventually crossed the coast in the north of Moreton Bay as an ex-tropical cyclone on the evening of 8 March 2025.

Maximum three second gust wind speeds around 100 kilometres per hour were experienced across the impacted zone from Redcliffe to Cape Byron. These lower than originally forecast wind gusts were not high enough to lift debris off the ground to become wind-borne. Even branches landed close to the tree from which they fell. The lack of wind-borne debris meant that few windows were broken. If the winds were 20 kilometres per hour higher, then the winds would have started to lift more roof tiles, pick up trampolines, garden sheds and rubbish bins and cause fallen branches to fly further. The low wind pressures and the lack of wind-borne debris contributed significantly to the low levels of structural damage in the area.

In these ways, the weakening of TC Alfred just prior to landfall meant that the large population in south-east Queensland and north-east NSW ‘dodged a bullet’. Had the wind been closer to the 140 to 155 kilometres per hour gust wind speed that the Bureau was forecasting for this category 2 system, the level of structural damage could have been very different.

The peak gust measured was 82 per cent of the design serviceability wind speed and 55 per cent of the design ultimate wind speed for importance level two buildings.

Even at the relatively low wind speeds in the event, some buildings in poorer condition were structurally damaged and wind-driven rainwater entered many buildings. The low incidence of structural damage meant that for the majority of buildings, rainwater ingress was through an undamaged building envelope. Water entered through closed windows and masonry blockwork at wind speeds less than the serviceability wind speed. Weatherproofing systems of buildings need to improve to strengthen community resilience.

Some issues associated with tall residential buildings were observed. In addition to the weatherproofing, there were issues with pedestal-mounted pavers on balconies, windows at or near ground level and differential pressures within buildings which prevented occupants from opening their apartment entrance doors. The event also highlighted the dependence of these buildings on power and the need to have reliable backup power sources for essential services such as operation of sump pumps, lifts, fire equipment and emergency lighting. Several aspects for improvement are noted:

• messaging for future tropical cyclones in this area
• selection of corrosion-resistant materials for hidden structural elements
• weatherproofing for buildings
• fastening balcony pavers
• resilience measures for tall buildings.