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jfribrg
2008-Sep-05, 02:05 AM
I was wondering where the definition of hurricane came from. The definition is a tropical rotating storm with wind speeds of at least 74 miles per hour, or 64 knots. These are not round numbers (in base 10 anyway), so I'm not sure why 74 mph and not 75 or 73 mph. I wonder if it has anything to do with the minimal speed in which an eyewall can form or something like that. I did a web search, and found many sites that explained the saffir-simpson scale, but nothing explaining why 64 knots. Any ideas?

Jim
2008-Sep-05, 02:42 AM
No particular reason, it's just a qualitative measure from the Saffir-Simpson scale.

http://www.ihc.fiu.edu/about_us/about_hurricanes.htm

Ivan Viehoff
2008-Sep-05, 09:14 AM
Not Bob Simpson (of Saffir Simpson) but George Simpson.

And we should also blame Sir Francis Beaufort, an Irish admiral, who invented the Beaufort wind scale. George Simpson modernised it to relate Beaufort force numbers to particular wind speeds.

A hurricane is force 12 on the Beaufort Scale, the highest on Beaufort's original scale, from the days when a dozen was a round number. So that is Beaufort's contribution.

The Wikipedia article shows Simpson's formula which relates Beaufort number to wind-speed, which modernised the Beaufort scale from 1946 onwards. This relates w (wind-speed in m/s at 10m above the ground) to B (Beaufort number) as follows:

w = 0.836 B^(3/2)

Beaufort force n, where n is an integer, is actually the range B=n-0.5 to B=n+0.5. So to get the minimum wind speed of a hurricane so you have to put B=11.5 into that formula to give you 32.6 m/s, which is the minimum wind-speed of Beaufort Force 12, a hurricane.

The Saffir Simpson hurricane scale is different from Beaufort, but has aligned its definition of a minimum hurricane to the Beaufort scale. Likewise the other hurricane scales Fujita and TORRO.

http://en.wikipedia.org/wiki/Beaufort_Wind_Scale

BigDon
2008-Sep-05, 04:57 PM
Nice condensing of the subject Ivan.

mugaliens
2008-Sep-05, 08:18 PM
Essentially, it is the wind velocity in which a man might be expected to walk on solid ground without being blown over. At any higher velocity, he would not be able to maintain his footing.

pumpkinpie
2008-Sep-05, 08:25 PM
Essentially, it is the wind velocity in which a man might be expected to walk on solid ground without being blown over. At any higher velocity, he would not be able to maintain his footing.

A woman would have no problem, though. ;)

JustAFriend
2008-Sep-05, 10:26 PM
Essentially, it is the wind velocity in which a man might be expected to walk on solid ground without being blown over. At any higher velocity, he would not be able to maintain his footing.

Let me fix that for you:

Essentially, it is the wind velocity in which a man might be expected to walk on solid ground in spite of being yelled at by his wife.

http://www.faithwebbin.net/images/features/nagging.jpg

:lol:

KaiYeves
2008-Sep-05, 11:17 PM
As for the etymology of the name, Hurikan was a Caribbean god of storms.

Lord Jubjub
2008-Sep-06, 12:10 AM
In terms of hurricane appearance, right around hurricane force is when an eye usually appears. The stadium effect usually is apparent around Cat 3.