After looking at the weather for the time robyn disappeared i think that theres no way she tried to swim out in those conditions .
The stats for the 8th and 9th are extreme .
On the 8th it rained copious amounts all day .
Windy sou westerly winds and a big swell running .
Both days very low temperatures .
"Coldest day10.9 °C at Bickley on the 8th"
"Coldest night-0.5 °C at Karnet on the 9th"
"Strongest wind gust89 km/h at Rottnest Island on the 8th"
http://www.bom.gov.au/climate/.../wa/archive/201508.perth.shtml
I think if robyn went to city beach and got out of her car and was alone then her disappearance did not happen in the ocean .
Can you imagine near zero degrees overnight and raining all day on the 8th and 9th .
She goes swimming and isnt washed ashore ?
I think that could only mean she swam out a long way but thats a navy seal type feat in such extreme conditions and big waves .
If her death in the ocean occured close to shore , eg the groyne,
she most likely would be found during the searches in the days after by the large scale search that police carried out.
The winds were favorable (being onshore on the 10th.)
This is an archived forecast from the windguru website that supports all the bom.gov info and my weather analysis .
Circled is 4m swell (from the moment RS went missing and sustaining all day )
Major cloud cover every day around the time also.