Spent last night anchored in Shark Bay behind Cape Upstart just north of Bowen.

We experienced winds sustained above 30knts but gusting over 40, highest was 44Knts.

No models had it forecast, nothing on any local forecasts either. It lasted about 4 or 5 hours and then at 2130 it just switched off. Within a half hour we had 10knts from the opposite direction. What would cause that kind of intensity and then just stop.

That is bizarre, I'll be scared to anchor there on the way back now.

Yes it was SE, the cape itself is quite tall with steep hills but something bigger than katabatic winds was happening. It had been between 10 and 20 knts all day but as we were coming past the cape I decided to put a second reef in before we gybed as the wind and sea were building. Nothing alarming was just being cautious as 2 days before we got caught in a squall between islands with some nasty wind on tide conditions and that was still fresh in the memory.
It was starting to gust up to 30 before we got behing the cape, anyway we anchored and just thought glad we got in before the wind blew up. Did the normal stuff tidying up lines and zipping sails in bags etc. I caught a Spotty Mackeral on the way so had to fillet that, I set up the railblaza bait/filleting board on the push put but then decided the fish would blow away if I put it there so ended doing on my knees on deck. Threw the frame overboard and it just took off downwind as soon as it cleared the lifelines.

So we had dinner, spotty macks are delicious, didnt think to much about the wind. 30 knts gusts are not uncommon on anchor but it just kept building. I had left the plotter on so we could see our anchored position and the gusts. The 30knt gusts went mid 30s than high 30s than we started seeing 40s and it wasnt dropping below 30. A couple of anxious hours. We were getting ready to do anchor watches, I went and lay down at 9.00 and said to my partner wake me at 10. About 9.15 it just started winding down, by 9.30 it was done. I went on deck at 10.00 and we had a 10knt northerly.

That's my story, and my tip is if your deciding what anchor to get, go for the biggest you can fit.

Sydney southerly busters are like that. You can set up for a nice BBQ in bay with gentle northeaster then suddenly theres a 15 minute southerly gale with rain and hail. Get some warning though, big dark clouds approaching.