Stewart, could these values be in km/h rather than knots? 100km/h and 80km/h are 54 knots and 43 knots respectively, which are reasonable values for a severe storm (although still dangerously extreme if you're out sailing).

According to Bureau of Meteorology data, the maximum recorded three-second wind gust in the Perth area was 43.2 m/s (84 knots) on 20th August 1963. This was at the City West recording station which had a height above datum of 58m and a mast height of 22m. One would assume the gust speed at water level was somewhat less.

Statistical work by Geoscience Australia predicts that a 100 knot gust in the Perth area is a once in 500 year event:


Similarly, a 80 knot gust in the Perth Area has a predicted frequency of once in 50 years:


Source: Geoscience Australia: SEVERE WIND HAZARD ASSESSMENT IN METROPOLITAN PERTH (Large PDF)