The weather has collapsed horrifically, with the Emperor at or approaching peak season (depending on whether you're at an early- or later-flying site...). Few eggs will have been laid yet.
The butterflies get decimated, in the modern sense of the term (such that one in ten survive), by gales, especially nocturnal gales and in particular the males (the females tend to roost lower down). The wind during the night of June 28th-29th will have done untold damage.
The big hope is that there are still a number of pupae to hatch, even at the earlier-flying sites.
This could be a longer than usual flight season, as some early-developing larvae pupated around May 21st whilst some late ones didn't pupate until mid-June, after the ten day cold period in early June.
Whatever, it is now clear that 2020 is not the annus mirabilis for the Purple Emperor that I and others had so eagerly anticipated.... Numbers at Knepp and the nearby woodlands have been decidedly disappointing (and Knepp is heavily prone to wind damage, being a more exposed site).
However, whereas other butterflies have bad seasons, there is no such thing as a bad Purple Emperor season. Keep going, to the end, and beyond!
Here's a couple getting plastered on oak sap at Knepp, from June 26th -