Folks,
Except as detailed by our mate Bloggsie, (and one other area) Australia is about the only country I know where a PPL or higher licensed pilot is NOT automatically an approved weather observer, and the (un) reason is so very Australian.
Back in late '60's or early '70's there was an industrial fight between whichever union covered the bulk of weather observers and BoM and DCA, ie: the Commonwealth.
One of the outcomes was (much to us "drivers airframe" surprise) regulatory change from an industrial agreement that pilots ceased to be met observers. It was never anything to do with "safety", but try telling that to a current generation FOI.
The other "exception" was (is?) where there is an M on a position, where you can broadcast a full Airep, and last time I noticed, if you want to report anything elsewhere, you must use the magic words "---- Airep SPECIAL".
In the discussions on TS in the vicinity, again the last time I looked, as the forecast applies to a 5nm radiius, vicinity was defined in the ICAO books 5 to 10 miles, so legally TS in the vicinity (between 5 and 10 miles) does not mean an alternate must be carried.
Of course, what might be prudent is another thing altogether.
Tootle pip!!
PS: Re. European or US "alternate always required", in general, their alternate criteria are lower than here, often a lot lower, and possible alternates are commonly a long spit away, not Australian distances. The US has a provision where the alternate fuel is not required, but I am not going to try and quote it from memory, but essentially the destination must be forecast VMC for quite a time span around your ETA.