You know what, I don't measure the temperature with a wet thermometer & a dry thermometer in a louvred box that sits in the ideal location & then split the difference. Instead I have a digital thermometer in the bow. Being a steel narrowboat that is soaking up the heat from the sun & then radiating it back out, in a marina with a whole bunch of other steel narrowboats doing exactly the same thing, sheltered from the wind, therefore giving me a higher temp than what the met office would say. Presumably that also means the side of the boat facing the sun wasn't too hot to touch for more than 5 seconds either. Maybe it also means the river wasn't frozen last year.
I just say the temp that the digital thermometer reads, after all I'm not doing scientific research so it really doesn't matter.
I guess this didn't happen last July either seeing as the highest recorded temp was 35.3°C in July last year in Kent, try telling it to the guy that was down in the engine hole!