Transition

[Magpie]

summer simmers down
as September settles in
feel Her sublime touch

the cool approach of Autumn
when the Artist lifts Her brush

Hi Mark, this is good. I see it observes a 'tanka' structure in the sense of a syllable count but also in the way that the final couplet is a response to the 'haiku', as it were. I like this nod towards the format.

The alliteration in the first section is good. I feel like there should be an em dash before the third line.
The repetition of 'the' in the couplet could be eliminated and it might work better. The last line is perfect so the first line could be something like 'Autumn's cool approach... ' 'begins' but better a word choice. 
Just a couple of thoughts.

Cheers for the read.