Are you, perhaps, unaware that these are in different units? 38.7C is 102F. The UK switched in the 60s to centigrade[0]. I'd also be suspicious of the accuracy and method of temperature collection in 1911.. the Met Office didn't start collecting data until 1914, and of the source accuracy.. Wikipedia[1] seems to suggest 98F (36.7C) and in another town. It certainly was extremely hot that August in 1911... especially without modern conveniences.
[0]: https://en.wikipedia.org/wiki/Metrication_in_the_United_King... [1]: https://en.wikipedia.org/wiki/1911_in_the_United_Kingdom