Earlier today following a US Air Force Reserve Hurricane Hunter reconnaissance flight into Hurricane Jimena off the southwestern tip of the Baja Peninsula, the National Hurricane Center in Miami, FL announced that Jimena was a strong category 4  hurricane on the Saffir-Simpson Intensity Scale with winds at 155 mph.  That brings it very close to the threshold of a category 5 hurricane (160 mph sustained winds at the surface) and that it was the strongest tropical cyclone anywhere in the world for the entire 2009 tropical season thus far.

The statement “strongest tropical cyclone” may be confusing for some, since Tropical Cyclone Hamish was rated as a category 5 storm by Australia’s Bureau of Meteorology (BOM) earlier this year.  So how could a category 4 cyclone be stronger than a category 5 cyclone?  It can’t – unless each storm was rated on a different intensity scale, which is the case with Tropical Cyclone Hamish and Hurricane Jimena.

The National Hurricane Center uses the Saffir-Simpson Hurricane Intensity Scale to rate tropical cyclones, and the BOM uses what is called “The Australian Region Tropical Cyclone Intensity Scale”.   Here are how the two stack up side-by-side:

For you Americans who have read this far, you can easily see by just the KM/H wind speeds that a category 5 storm on the Australian Scale is a category 3 storm on the Saffir-Simpson scale used by NHC.  So by American standards Tropical Cyclone Hamish was a “major” hurricane (cateogry 3 or higher on the Saffir-Simpson scale), but far from being what would be considered as a Category 5  if it were to be rated by the NHC.

Tags: forecasting, hurricane