Phil that bump that was a lot worse has now changed and got better.
The way I see it is that bump changes the wind direction a bit making it more difficult for the thermal effect to work.
I figure the wind is traveling sort of parallel to the lines except that it is also trying to get from the high to the low so I then add roughly another 30 to 40 degrees to the lines.
So on the old fridays synoptic the majority of the morning wind for WA was traveling in a SE direction except for that bump over Perth which made the angle more Easterly say EESE
I then figure that this direction is harder for the thermal wind to push against creating a weaker breeze than predicted.
I also think the pressure readings taken from the various locations can vary from how many locations the readings are taken from and then the synoptic pattern is then roughly plotted out eg a map based on 100 different readings would be less accurate than one based on 1000 pressure readings.
This isn't fridays map just one i quickly grabbed this am