Take a look. Camborne 22% at 15:00. Remarkably it was 69% at 11:00, but only 25% an hour later. Somewhat higher at Cardinham - nearer 40%.
The sharp drop in humidity shows up well here at John Chappell's Land's End site.
http://www.landsendweather.info/met/mainframe.htm
Also notice the strong & very gusty winds associated with the arrival of the low humidity.
Unbroken warm sunshine - but some very interesting variations.
Graham
Penzance