Modified Saffir-Simpson Scale Effective May 2012

[toxictwister00]

http://www.nhc.noaa.gov/news/20120301_pis_sshws.php

Effective May 15, 2012, to resolve these rounding issues,
Category 4 on the SSHWS will be broadened by one mph at each end
of the range, yielding a new range of 130-156 mph.  This will
also result in a minor modification of the Category 3 and 5 wind
speed thresholds. The SSHWS will change as follows:
 
From:
 
Category 3: 111-130 mph (96-113 kt, 178-209 km/h)
Category 4: 131-155 mph (114-135 kt, 210-249 km/h)
Category 5: 156 mph or higher (136 kt or higher, 250 km/h or
            higher)
 
To:
 
Category 3: 111-129 mph (96-112 kt, 178-208 km/h)
Category 4: 130-156 mph (113-136 kt, 209-251 km/h)
Category 5: 157 mph or higher (137 kt or higher, 252 km/h or
            higher)
 
There will be no change to the wind speeds currently assigned to
Categories 1 and 2.
 
With this change, a 115-kt Category 4 hurricane will have its
intensity properly converted to mph and rounded to the nearest 5
mph (130 mph) and remain within the Category 4 mph range.

[TWCCraig]

Interesting 

[Zach]

They're modifying it again? They just modified it 2 years ago to become the Saffir-Simpson Hurricane Wind Scale

[phw115wvwx]

It's just a minor tweak so that taking a hurricane's wind speed to the nearest 5 kt, converting it to mph, and then rounding to the nearest 5 mph doesn't cause a contradiction of a hurricane's classification.  If you had a 115-kt hurricane (defined to be Category 4), which converts to 132.3 mph, you would end up rounding down to a 130 mph hurricane (Category 3 on the older scale, Category 4 with this tweak).  See it now?  If you're wondering, the above converting and rounding with wind speeds is how NHC handles all tropical cyclones.

The name change earlier that Zach mentioned was just to emphasize that this scale only classifies hurricanes by winds alone.  We found through studies of recent landfalls that the magnitude of the hurricane's winds don't always correlate with the intensity of other hazards like storm surge.

[Lightning]

Will this change help the winds in a major hurricane to be more consistent with its minimum central pressure? For example, Hurricane Katrina was a category 3 storm with winds of 125 mph, however, its pressure, 920 milibars, which is consistent with a category 4 hurricane (nearly a 5).

[phw115wvwx]

Will this change help the winds in a major hurricane to be more consistent with its minimum central pressure? For example, Hurricane Katrina was a category 3 storm with winds of 125 mph, however, its pressure, 920 milibars, which is consistent with a category 4 hurricane (nearly a 5).

It has nothing to do with pressure or anything else.  This scale only uses wind speeds to classify hurricanes, which is why it was renamed from the Saffir-Simpson Scale to the Saffir-Simpson Hurricane Wind Scale.