He said this month was set to become one of the wettest June's on record.
Look, Mr BBC man, that's a possessive apostrophe. The June's what? Its days, its nights, its weather?
If you can reverse the word order and use the word 'of', you need an apostrophe, immediately after the word in question.
The book of the boy = the boy's book.
The curls of the girls = the girls' curls.
The (what?) of the June = what passes for literacy at the BBC.
I learned this in, I think, Junior 2 at the age of about 8. Point is, so did the other 29 in the class I was in. And many of them were not Mastermind contenders by any means. The teacher taught it, we practised it, we got it right. And I still know it half a century later. It ain't hard, folks.
I think what has happened here is that the writer has written 'Junes' (quite correctly) and then thought that it looked odd, and added an apostrophe because, well, because. Words that end in vowels sometimes do this to people, although it's usually things like 'radio's' as a plural of 'radio', which look a little odd on their own. I think it comes from a fear of getting it wrong, which is OK for a ten-year-old, but laughable in a professional employee in the media. The correct form, 'radios' looks a bit like it ought to be pronounced 'rad-ee-oss', and I can sort-of forgive this one. Similarly with decades, where a lot of people write 1960's. Not necessary, but understandable. But 'June's'? Pfft.
SIMPLE RULE 2:
A straightforward plural does not need an apostrophe. More than one boy, 'boys'. More than one scenario, 'scenarios'. More than one June, 'Junes'.
Really sorry about the flooding, folks. Bucko has some 'live' photos that bring the message home.