Rough guide= 15 days at 17 mean = 235 degrees.
A monthly mean of 18 requires 31x18 = 558 degrees.
Current deficit to 15th = 323 degrees.
This spread over remaining 16 days requires 20.2C per day everage.
Yesterday will have been below that but although today through Tuesday should easily exceed that and give us some to spare, beyond is still uncertain and no prolonged hot spell is in the models although hints of some more hot days here & there.
I reckon at this stage we will be looking at mid 17s at best, but of course I won't pretend to see beyond Wednesday.