...According to the BBC they are gonna need it:
Meteorologists have upgraded Cyclone Yasi to a category five storm, the most severe level. With winds of almost 300km/h (185mph), they are warning it poses an extremely serious threat to life and property, especially around the cities of Cairns and Townsville. People in low-lying areas especially are being urged to evacuate.
I've not been able to find an updated forecast that reflects the Category 5 designation. The last advisory listed at HurricaneZone.net has a time stamp of 0000UTC (10am Queensland time - it's 2:20pm now), and they still say "125 KT, GUSTS 150 KT" with a forecasted high of "130 KT, GUSTS 160 KT" which would mean a strong Cat 4 storm.
Now, it could be the Australians have other assets they can use when dangerous storms loom. The general practice in that part of the world is to rely on satellite images to pinpoint position and make a guesstimate of wind speed based upon the visual organization of the storm. However, I'm not seeing any reference to pressure readings, so it doesn't seem the upgrade is based upon instrumental measurements.
Either way this is a bad storm coming at a bad time for already weary Queenslanders.
Ah, here is the issue with the Cat 4 vs. Cat 5 designation. The Australians do not use the Saffir-Simpson scale as we do in the states. In Australia any storm over 107kt is classified as "Category 5" while a hurricane hitting the U.S. at 108kt would be called a strong Cat 3 storm. So a 130kt storm, like this one, would be a Cat 4 for us and a Cat 5 for Aussies. (Info gleaned from WUWT.)