I agree there was a weak cold front over the south west of Perth, but the isobar was still 1012 hardly low or very low. That is a high pressure system of 1016 over shark bay in your image not a cold front as you said in your post above. It is clearly shown in my map of 17th June. I'm not sure if your image is of the same day, although similar. It is basic Yr 10 geography. I'm just trying to put the correct facts out there are make sure they do not get distorted.
Metic you have been quoting of random 7 m swells and NW winds off Cape Naturaliste way off of lower south west of WA. That is incompatible winds and swell size as reported for Perth metropolitan on the dates around JC's disappearance
Sorry PD, high pressure systems are anti clockwise, but the weather does move west to east as a system. All the coloured maps you posted metic clearly show a very low pressure system or very very low around 41 or 42 degrees South, so half way to Antarctica around 17th June 1988. That takes about 6 days to arrive in Perth on Friday 24th June.
Source West Australian Sat 18th June 1988
Saturday 18[SUP]th[/SUP] June 1988: Morning showers. Outlook fine. Temp 14 20. A high pressure ridge was located across the centre of the continent and was producing fine clear conditions with easterly winds in the northern half.
Extended forecast
As the high pressure ridge moves further southwards a return to fine conditions in inland areas should result by this afternoon. Coastal regions should experience isolated showers early this morning. Another weak front should pass near the southwest corner tomorrow, but showers associated with this system should be confined to the far southwest coast.
Sunday 19[SUP]th[/SUP] June 1988: Temp min 13.6 at 8.50 pm and max 20.6 at 11.45 am.
Monday 20[SUP]th[/SUP] June 1988: Temp min 10.7 at 7.30 am and max 18.4 at 2,25 pm. SW winds at 10 to 15 knots easing to 10 knots by late morning.
Tuesday 21[SUP]st[/SUP] June 1988: Forecast Perth fine and cool. North East winds 5 to 12 knots. Seas should be 0.5 m on a swell to 2.5 m. Temp 8 19 degrees.
Extended forecast: With a high pressure cell establishing itself over the southern half, fine conditions should persist over the State until late tomorrow. A front should approach the coast tomorrow night and cross the lower west coast on Thursday.
Wednesday 22[SUP]nd[/SUP] June 1988: Forecast Fine. Outlook showers developing. Temp 10 20.
Fine and sunny conditions prevailed through the northern half, while the southern half experienced similar conditions at 4.00pm yesterday. A high pressure system was located over the Eucla and is presently bringing fine weather to almost the whole state. These conditions should persist except for the extreme SW corner where isolated showers are forecast. With clear skies and light winds inland areas should be in for another cold night with local frosts in the southern half. The seasonal fine weather should persist in the northern half.
Source: The West Australian June 17th - 22nd June 1988.