Lead Balloon
If the “Heavy Rain” means that the runway is contaminated, ie >3mm of standing water on >25% of the runway, FlySmart would be used prior to dispatch with forecast conditions and Medium-Poor braking, medium auto brake idle reverse x 1.15.
If “Heavy Rain” means the runway is wet, 1.92 x LDR dry would be used.
In both cases a landing performance would be calculated inflight using FlySmart with actual conditions, the actual landing weight, medium-poor braking if using idle reverse, medium auto brake x 1.15. If too short, recalculate with full reverse. If still too short recalculate with manual braking. Finally if still to short divert to your alternate. Where I fly we always carry an alternate but in the Australian context, an alternate probably should have been planned for based on the info you’ve provided.
I had a flight a few years ago into Perth with an A350-900. Forecast for Perth was a Tempo TS and rain with wind straight down RWY21 at 30kts. We don’t use 06/24 unless operationally required due to the shorter LDA. Also we normally plan Perth as an Island Reserve (2 hours holding Fuel) due to limited available alternates but on this night Dispatch planned Adelaide as an alternate due to WX. During the flight WX forecasts for Perth started to deteriorate with heavy rain, TS and winds straight across RWY 03/21 at up to 50kts. ATC had closed this RWY but in addition it was above the max Xwind for the A350. Rwy 24 was the only choice but with Medium-Poor braking and idle reverse, the Rwy was too short. I recalculated with full reverse and the numbers worked, just. I recalculated again with manual braking which gave me more fat. Based on the numbers we were going to have to exit Rwy 24 at the end via V but in the end was able to exit via A.
The point I’m making is that if on the day, the numbers don’t work make sure you have a plan B, preferably an alternate.