Where were all the migrant warblers?

31st August 2018 – bright and sunny SE2 then S3/4
The sea provided 320 Sandwich Tern, 30 Common Scoter and a Shag.
Grounded Migrants
Sightings were sparse with just 5 Wheatear and single Garden Warbler, Blackcap, Sedge Warbler, Willow Warbler, Whitethroat and Goldcrest logged.
Diurnal Migration
In contrast the skies were far more productive with observations (0700-1100) producing totals of 1250 Meadow Pipit, 1000 Swallow, 100 Tree Sparrow, 100 Pied Wagtail, 62 Sand Martin, 41 Goldfinch, 32 Linnet, 11 House Martin, 6 Grey Wagtail and a Tree Pipit.
Wildfowl and Waders
Waders included 6000 Oystercatcher, 1300 Redshank, 350 Turnstone, 10 Black-tailed Godwit and 10 Greenshank.
Perhaps the worst August total ever recorded by the observatory was typified with the lack of warblers trapped with just two Willow Warbler ringed. Only 69 birds of seven species were handled during the month, individual species totals were as follows (retaps in brackets) House Sparrow 49, (1), Goldfinch 8, (1), Greenfinch 5, Willow Warbler 2, Blackbird 1, Blue Tit 1 and Coal Tit (1). 637/30, 156/15, 7/5.
A Pinion-streaked Snout was the highlight of the overnight attraction.