hurricanes and tornados

Factual Questions
1

Are there limiting factors in the speed and duration of hurricanes and tornados. I have heard of tornados in the 300 mph range. Is that a max?
Is a cat 5 the max for a hurricane or do we need changes. How long can they last?

2

http://www.nhc.noaa.gov/aboutsshs.shtml

Basically, hurricane categories are based on wind speed and storm surge, although wind speed is the primary. A cat 5 has wind speeds over over 155 mph and the national weather service site says only 3 cat 5’s have hit US land since they started keeping records. (though wasn’t Katrina a cat 5? maybe that number should be 4) Since there’s no upper limit on what defines a cat 5, it would seem that no changes are needed.

http://www.charmeck.org/Departments/Emergency+Management/Hazards/Natural+Disasters/Tornado+Categories.htm

Tornados are also classed by windspeed, from F0 to F6. According to that site an F6 has never happened and is refered to as an Inconceivable tornado as it’s expected to not ever happen. F6 wind speeds are 319-379 MPH. It would seem that 300 is probably considered the upper limit for tornados.

3

A tornado probaly has more limiting factors. Hurricanes can ‘get lucky’ and ‘live’ in almost idle positions, over ideal waters, with no shear(sheer?) or steering winds.

Cat 5: Storms that hit Cat 5 don’t stay there that long. The conditions are so unfavorable that life at Cat 5 is often less than one day.

Cat 5 landfall, the catch 22: As storms get close to landfall, they are in less-than-ideal conditions, so it is unlikely that a Cat 5 would make landfall. However, as I have ranted in the Pit more than once over the ratings:

When reporters note that a storm has ‘weakened’, your roof, the trees, structures and miscellaneous buildings don’t care if the 170 MPH winds are now 160! They are coming apart, up, off – whatver. -end rant.

At Cat 4 thru 5, plus the stronger Cat 3 storms, it’s all one group of bigazz killers. Some Cat 3 storms are more dangerous than 4’s because they cover a larger area, and the duration of the winds is greater, or because the eastern side strikes first, etc, etc.

We are fixated on categories, and often times the fixation has misled people as all they hear about are storms ‘weakening’. Yeah, they usually do, but it hardly matters - end rant

4

Katrina was a Category 5 at one point, but dropped to Category 4 before actually hitting the US.

5

Thanks. I didn’t remember the exact timeline on that.