The forecast maximum temperatures in spring are nearly always too low in Penzance (as I believe, is often the case, in Wembury). In Penzance this discrepancy is biggest wih an offshore breeze, as little account seems to be taken of the wind direction. Today the discrepancy was accentuated by the frontal cloud arriving later than forecast.
So forecast on the MetO site for Sennen as at 12:40
The forecast temperatures were identical for Penzance, despite it being spring and the wind onshore at Sennen, offshore in Penzance. (This is a feature of the postcode forecasts which is up there with no allowance of salt spray in the visibility forecasts)
A quick look at the webcams suggested something different, so I went off for a walk at Sennen. Around 13:30
In practice the maximum was 13.3C in Penzance, reached around 14:00.
Clouded over now (15:30) but still bright with the sun visible.
Lucky we have webcams!
Graham
Penzance