Hurricane Isabel is the strongest Category 5 in 15 years.
It was Hurricane Gilbert (Sep 8-20, 1988) which topped 160 mph for six hours only but remained a category 5 for 18 hours. Press: 888 MB
Andrew's (Aug 16-28, 1992) speed topped 150 mph and lasted six hours only but remained a category 5 for 12 hours. Lowest pressure was 992MB.
Hurricane Mitch (Oct 22 - Nov 9, 1998) wind speed was 155 mph and last 12 hours at that top speed. It remained a Category 5 for 30 hours!! Press: 905 MB
This is an edited message in response to all the responses below
The source which I used for my information was UNISYS. If the speeds are listed in knots then Mitch would have topped 178 mph.
The official record for Mitch (http://www.nhc.noaa.gov/1998mitch.html) shows a top speed of 155 KTS which means that in fact Isabel is no where near as strong as Andrew, Gilbert, or Mitch as I had earlier indicated.
Please accept my apologies. I did not set out to intentionally mislead.
ANDREW:
http://weather.unisys.com/hurricane/atl ... index.html
GILBERT:
http://weather.unisys.com/hurricane/atl ... index.html
MITCH:
http://weather.unisys.com/hurricane/atl ... index.html