How are we do this?
How much warmer than average and for how long?

Can I suggest:
Max daily temp 2 degrees C above average any time in the autumn
months of Sep. to Nov.
and for more than one day.

The average (over last 10 years) max for Wembury for the last week of
September
is 17.5C.
So I will be looking for 19.5C.

The forecast discombobulated upper trough, cutting off the N. Atlantic
air, and giving a SE wind is the business, and is likely to easily
give max temps of 20C or more.

The last time we had such conditions around here in the last week of
September
was in 1985.
Plymouth Mt Batten recorded
26 Sep 21.2C
27 Sep 21.4C
28 Sep 20.3C
29 Sep 20.7C
30 Sep 21.0C

Indian Summers have occurred in Wembury in the third week of Sep.
1998
and Sep. 2006 with a max in excess of 20C for 3 or 4 days in a row.

Len Wood
Wembury, SW Devon , 83 m asl