disoswam
Structural
- Jun 15, 2011
- 16
Am I understanding this right? 200mph Saffir/Simpson = 220mph ASCE7-10 (extrapolating C26.5-2 since all speeds over land are 1.1x Saffir) = 248mph ASCE7-10 (using the Durst Curve 60sec water = 1.25; 3 sec Exp C = 1.55).
Hurricane Patricia became the most powerful tropical cyclone ever measured in the Western Hemisphere on Friday morning as its maximum sustained winds reached an unprecedented 200 mph (320 kph) over water as reported by The Weather Channel and NOAA.
C26.5.1 The wind speeds used in the Saffir/Simpson Hurricane Scale are defined in terms of a sustained wind speed with a 1-min averaging time at 33 ft (10 m) over open water. The ASCE 7 standard by comparison uses a 3-s gust speed at 33 ft (10 m) above ground in Exposure C (defined as the Basic Wind Speed, and shown in the wind speed map, Fig. 26.5-1). An approximate relationship between the wind speeds in ASCE 7 and the Saffir/Simpson scale is shown in Table C26.5-2. The table provides the sustained wind speeds of the Saffir/Simpson scale over water, equivalent intensity gust wind speeds over water, and equivalent intensity gust wind speeds over land. The gust wind speeds over water use a gust factor taking into account basically the same sea surface roughness wind speed >30m/s. For a storm of a given intensity, Table C26.5-2 takes into consideration both the reduction in wind speed as the storm moves from over water to over land due to changes in surface roughness and also the change in the gust factor as the storm moves from over water to over land [Ref. ASCE7-5, C6-22]. It should be noted that the sustained wind speed over water in Table C26.5-2 cannot be converted to a peak gust wind speed using the Durst Curve from Fig. C26.5-1, which is only valid for wind blowing over open terrain (Exposure C).
Hurricane Patricia became the most powerful tropical cyclone ever measured in the Western Hemisphere on Friday morning as its maximum sustained winds reached an unprecedented 200 mph (320 kph) over water as reported by The Weather Channel and NOAA.
C26.5.1 The wind speeds used in the Saffir/Simpson Hurricane Scale are defined in terms of a sustained wind speed with a 1-min averaging time at 33 ft (10 m) over open water. The ASCE 7 standard by comparison uses a 3-s gust speed at 33 ft (10 m) above ground in Exposure C (defined as the Basic Wind Speed, and shown in the wind speed map, Fig. 26.5-1). An approximate relationship between the wind speeds in ASCE 7 and the Saffir/Simpson scale is shown in Table C26.5-2. The table provides the sustained wind speeds of the Saffir/Simpson scale over water, equivalent intensity gust wind speeds over water, and equivalent intensity gust wind speeds over land. The gust wind speeds over water use a gust factor taking into account basically the same sea surface roughness wind speed >30m/s. For a storm of a given intensity, Table C26.5-2 takes into consideration both the reduction in wind speed as the storm moves from over water to over land due to changes in surface roughness and also the change in the gust factor as the storm moves from over water to over land [Ref. ASCE7-5, C6-22]. It should be noted that the sustained wind speed over water in Table C26.5-2 cannot be converted to a peak gust wind speed using the Durst Curve from Fig. C26.5-1, which is only valid for wind blowing over open terrain (Exposure C).
