It is an attractive question, and my rendering would be something like this:

a relatively long fulte solo that culminate in the highest note to end in catharsis

I have a feeling that I am still not getting the right words, but hey, your English should be better than mine! Basically, components you need are:

- This solo ends in the highest note. Usually there is THE highest possible pitch that a flute can produce, and the text is saying that the solo ends in that single note played in forte, so I would use a singular, "note."
- To produce the highest note, the player needs to blow with much pressure on his/her lips and abdomen. This is one aspect of "tsuyoku" refers to. "Hukikiru" also means that the player uses up his/her strength to do it. So, having some refernce to physical energy would be good.
- From the listener's point of view, the highest note is usually loud and ear-piercing sound that strongly calls for your emotional reaction. This is another aspect of "tsuyoku."
- As the tension builds up with higher notes, it climaxes.
- Then lastly, after hearig the highest note, listeners will feel some relief from the tension.

I play shinobue flute maily with my taiko group, and higher notes are mainly used for matsuri bayashi kind of pieces. Another Japanese flute, Noh-kan, has extremely powerful high pitch sounds. This is one thing I would like to learn if I were living in Japan. Is this piece played with a European flute or a Japanese one?