Likewise I had even considered flying over to Bilbao for totality, but at that point the eclipse would be on the horizon (unique in itself), and too could be a washout.

It's free, not premium, here:

https://www.theweatheroutlook.com/twodata/eumetsat.aspx?view=geocolour®ion=es 

Here in Edinburgh, it's usually always cloudy or overcast at the time when there is a major astronomical event which is worth seeing but I suppose the law of average tells us my luck in that regard has to change at some point in time.

I'm lucky enough to be on holiday on the Isles of Scilly next week so am looking forward to a decent view. I was there for the eclipse in 1999 as well and the clouds parted at just the right time so we got a phenomenal show.

What I would say is that although the partial eclipse is special the true awe and wonder moment (imho) only really comes with totality. 

I remember watching the shadow race across the sea towards us, all the gulls flying up in confusion to roost, the chill that came with the darkness and then the lighthouses flashing on and the stars coming out.

It truly felt like the end of the world. My overriding memory though was the unexpected feeling of relief when the sun reappeared - quite a primeval experience. 

It's definitely somthing that I'd like to witness again in my lifetime. 

Still, it's definitely significant. I remember the large partial eclipse in March 2015 and so it will be comparable to that. At the height of it, it will feel noticeably cooler and feel a bit like a dull December day.

How is inter island travel? I was hoping to do a bit of Island hopping but not sure if it's feasible on a day trip. I've yet to decide whether I'll do a boat day trip or helicopter in and out, that said, on a day trip is it possible to do more than the main island?

I had pondered whether it was feasible to sail out to the totality line, but it's a lot further than I thought. As it stands I'll probably watch the eclipse from Land's end, stay overnight in Penzance and day trip to Scilly the next day before making my way back.

On topic, Looking reasonably positive for now on BBC Weather, but cloud looks dangerously close

Inter Island travel is very easy - there are regular trips and none of the journeys take more than 20 minutes so it's definitely possible to visit one of the Off islands on a day trip.

If you can push the metaphorical boat out to the cost of a helicopter trip then it's well worth it as you'll really maximise time over there. I'd consider flying into Tresco rather than the main island of St Mary's and then popping across to Bryher as that'll give you a real flavour of the islands. Depending on which day you go you should even be able to walk to Bryher from Tresco at low tide and then boat back.

I've booked the helicopter. I was considering Tresco but wanted to do St Mary's if I only had the choice of 1. Indeed, the Eclipse means it's going to be a low spring tide. It's saying that it'll be walkable at noon. Although landing at St Mary's at 11:53 might make it difficult to get over to Tresco (then Bryher) in time. We'll see.

For a 17:35 helicopter back, how soon would I have to be back at the airport?