I think La Niña plays a bigger role for the whole season than this. Where I am (Vancouver, Canada), I expect below average temperatures and above average precipitation. The presence of a weak polar vortex signals a higher risk of at least one strong winter cold snap in North America, but we won’t know specifics until much further along in the season.
I still am of the opinion that the vortex is in the early stages of forming and will be disrupted over the next several weeks by anamolous high pressure in Alaska/Siberia (possibly shifting eastward into October). The ECMWF op analysis on this website shows the lowering absolute temp and lowering 10 mb heights in the North Pole region over the past two weeks or so. Additionally, the circular stratospheric wind pattern is slowly returning (since about 9/7) and modeled to increase in the coming weeks.
Obviously it is not as developed as it will be later next month or as developed as the South Pole polar vortex currently is. I am curious to see how long the “heat wave” in Siberia/Alaska (and possibly the Canadian Arctic next month) lasts. I just think this pattern in the early stages of development plus La Niña foster conditions for sudden stratospheric warming events later in the season.
Edit to add: Is it a good forecast? I think so but maybe it will be and maybe it won’t, that’s just the nature of things. I stand by it though.