Large hailstorms are significantly more likely in southeast Australia during La Nina periods than in El Nino ones, while shifts between the climate drivers affect event locations, forecaster Weatherwatch says.

It was previously assumed La Nina conditions might suppress hailstorms along the east coast, but the weather intelligence company says it has found activity often shifts slightly away from major population centres.

Weatherwatch drew on its HailTracker database to understand patterns driven by climatic cycles.

“Our data shows a clear trend: the likelihood of large hail events in southeastern Australia significantly increases during La Nina conditions compared to El Nino periods,” MD Anthony Cornelius said.

“We’ve also identified distinct hail corridors, which shift depending on the ENSO phase. Remarkably, a difference of just 30-40 km can mean a five to six times variation in hail risk annually.”

The ENSO (El Nino Southern Oscillation) describes the swings between La Nina and El Nino events.

Mr Cornelius says in La Nina years, Sydney’s hail corridor typically covers the western suburbs; in neutral ENSO years the corridor expands across the metropolitan region.

The insights can help insurers refine risk assessments, allowing for more precise predictions and targeted underwriting decisions before hail seasons, he says.

Hailstorms have led to catastrophic damage. The Sydney event in April 1999 caused insured losses of $1.7 billion based on original values, according to industry figures.

The Insurance Council of Australia has estimated losses would have reached $8.85 billion if the storm happened in 2023, adjusting for inflation and factors such as changes in property numbers and values.

Weatherwatch says it plans to expand its climatological database to cover additional perils such as floods and heatwaves.