The cost to insurers of the hailstorm that hit Sydney last December could eventually reach A$1.5bn ($1.1bn) to A$2.0bn once all claims are reported and paid, which would make it one of the top five most expensive weather events of the past 30 years and possibly the most damaging hail storm since the Sydney hailstorm in 1999, says Firetrail Investment, an investment management boutique.