Both ECMWF and GFS have been, on and off, forecasting the end of the flat spell at around the 240hr mark for quite some time without this actually happening. However this morning ECMWF, GFS and a lot of the GFS ensemble runs are pointing to the high over Ireland starting to breaking down at around the 168hr mark. Considering that forecasts 168hr ahead are quite a lot more reliable than 240hr and the consensus between the longer range models I'm getting hopeful that the high may finally move off.
Unfortunately the most likely looking pressure set up once the high moves off is for a moderately deep area of low pressure to move across the top of the UK while high pressure builds back into mid Atlantic. So it looks like the flat spell could be followed by a heap of onshore shite and poor weather. If the high takes its time moving off there could be a window of opportunity for some swell to come in (probably from the ex-tropical Gabrielle low) before local winds turn bad.
However this new set up is not certain yet and something else is still quite possible.
I’d estimate that around 180hr ahead (16th Sep):
50% chance of the poor set up described above
25% chance of some other set up which could be better.
25% chance of the high being belligerent and hanging on in there over Ireland.