... there is TS in the actual weather, then alternate/holding fuel is required.
This idea doesn't work. Consider taking off from A for a long flight to B. Whilst loading fuel at A, a perusal of the forecast for B shows that there are no operational requirements at B. So, no alternate/holding fuel is loaded.
Then, during the long flight, and now 10 minutes away from B, the METAR for B suddenly mentions TS. Is it now the case that you need to be carrying alternate/holding fuel?
Of course not. The legal requirements were fully met before departing from A.
This must also be the case if an amended TAF for B (now forecasting TS) was issued 10 minutes out.
Can't find a current Aus TAF with VC, but here is the current one from Pago Pago ...
It must be the case for that place that they always use VCTS and never TS in their forecasts. This is probably more efficient than what we do here in Australia (i.e one code for Pago Pago, while we have two: TS and VCTS).
I'm pretty sure I've seen VCSH on a Aus TAF before though?
This would mean that the BOM have the forecasting accuracy to discern whether the thunderstorms are going to be within 5 miles (TS) or outside that (VCTS).
I don't believe they have that accuracy at the moment, which is why I say that in Australia, you will only see VCTS on a METAR or the report portion of a TTF - and being the
report portion means it is not the
forecast portion, which means the alternate/holding rules don't apply.