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Global Guide to Tropical Cyclone Forecasting:
Chapter 9: Ready Reckoner

9.5 USEFUL TROPICAL CYCLONE PARAMETERS

9.5.1 Tropical Cyclone Severity Scales

The Saffir Simpson Hurricane Scale (Simpson and Riehl, 1981) was developed to provide a sliding scale of damage potential for hurricanes, including that arising from storm surge. A similar scale, though adapted for local conditions is used in Australia. Global adoption of such scales is strongly recommended.

Hurricane or Severe Tropical Cyclone  Maximum Sustained Winds
Saffir-Simpson Australian Scale
Level (1-min mean, kt) (10 min mean, km h-1)
1 64-83 63-90
2 84-96 91-125
3 97-113 126-165
4 114-135 166-225
5 >135 >225

Some of the tables from the main text are also listed on the following pages for convenience.

9.5.2 Gust Factors

Table 4.2: Gust factors defined by the ratio of peak 2-s wind to the mean wind at 10 m elevation for various exposures and averaging times and in wind speeds of at least hurricane force. Parentheses give an indication of the range in gust factors. From Atkinson (1974), Spillane and Dexter (1976) and Padya (1976).

  OCEAN FLAT GRASSLAND WOODS/CITY

1-min Mean

 1.25 (1.17-1.29) 1.35 (1.29-1.45) 1.65 (1.61-1.77)

10-min Mean

 1.41 (1.37-1.51) 1.56 (1.51-1.70) 2.14 (1.89-2.14)

10-min Mean over Ocean

 1.41   1.31 1.11

 

9.5.3 Dvorak Intensity Relationship

Table 2.1: Empirical relationship between the current intensity number (CI), the Maximum sustained 1-min Wind Speed (MWS, kt), and the central pressure (hPa) in tropical cyclones. The central pressure values for the western North Pacific are from Shewchuck and Weir (1980).
  Central Pressure
CI MWS (kt) (Atlantic) (NW Pacific)
0.0 <25    
0.5 25    
1 25    
1.5 25    
2 30 1009 1000
2.5 35 1005 997
3 45 1000 991
3.5 55 994 984
4 65 987 976
4.5 77 979 966
5 90 970 954
5.5 102 960 941
6 115 948 927
6.5 127 935 914
7 140 921 898
7.5 155 906 879
8 170 890 858

 

Contents Chapter 9.6


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