Hi Francois,
May is not the best month, but you should still get some good sailing days, Broome is definitly not the spot for sailing but great for fishing..
We sail all year here. We had
21 days sailing last March,
14 days in April,
7 days in May,
12 days in June,
8 in July etc..
Just to give you an idea... May is not the good month but still !
email me if you want... I will help you

good wind