How bout all the above?
In something like the HH GFS run wave spacing is close enough to almost work together (northern stream and southern streams phase). As I suggested earlier, the northern stream (NS) energy is diving in on the back side feeding the coastal storm cold air.
The pattern depicted is not progressive (fast), and the SLP off the coast takes its good ol time coming up the coast and gives time for that NS energy to catch up and "dives in" on the back and bombs out off the coast. IF that would happen, thats called a capture/phase as one system feeds into the other (NS dives into SS (SLP off coast).
The excitement is seeing all pieces of the puzzle getting close to working in concert w/ one another. I'll not go much deeper than that cause thats the pros job, but hopefully my info in weenie terms helps to understand the elevated excitement.
Thats how I see it and if any disagree or have better disco to offer....share away.
All that said, Eskimos right, its a long ways out, and there's a bunch of good and bad runs likely to follow...so keep expectations reasonable. It's also been a long time since something like this has shown up inside 240 hours, so a tad of excitement is totally warranted IMO. I'm keeping a casual eye on it, and wont dive this deep on every run...too far out.