Sept the city thermal starts to die off so it's more about frontal systems and what's happening in the Straight. You should look to YVR TAF as your first go to for forecasting outside of summer https://wtfbc.ca/taf.php?station=CYVR
Keep in mind it's forecasting the wind at the airport, not at Spanish Banks.
Yesterday's wind was very strong - typically 16 knots but gusting over 30, with the peak gust hitting 40 knots. At 2:00 I went out on my foil with 6 m kite and after half an hour I got tired of being intermittently overpowered and came in.
I'm not sure that is representative of September in general.
Today had nice steady wind in mid afternoon. Many kiters were out. I have kited or winged at Spanish Banks 7 days so far this month and it's only Sept 10th. CG
Today was rather gusty but there were several of us out kiting. For the record I have had 17 days on the water at Spanish Banks this September either kiting or winging ..all on hydrofoils. October is typically good too but it gets a bit cooler of course..