Plymouth State Weather Center - Tropical Storm Criteria

Classification Criteria:

• Tropical Depression: Winds less than 34 knots or 39 mph and an organized circulation


• Tropical Storm: Winds 34-63 knots or 40-73 mph


• Hurricane: Winds greater than 63 knots or 73 mph

Saffir-Simpson Intensity Scale for Hurricanes used by the National Weather Service (NWS)

Starting with the 2011 hurricane season, the NWS began using only the wind speed criteria of the Saffir-Simpson Hurricane Scale, since surge specific categories could bring differing impacts due to local characteristics. The wind thresholds remain the same as the original sclae listed below. For more detailed information on this scale and surge forecasting, please refer to the following NWS pages:

• The Saffir-Simpson Hurricane Wind Scale (pdf)
• The Saffir-Simpson Hurricane Wind Scale Summary Table (pdf)
• Storm Surge Scales and Storm Surge Forecasting (pdf)

Original Saffir-Simpson Intensity Scale for Hurricanes

• Category 1
• Maximum Wind: 64-82 knots or 74-95 mph and/or


• Lowest Surface Pressure: above 979 mb or 28.91 in. Hg and/or


• Storm Surge: 4 to 5 feet above normal


• Category 2
• Maximum Wind: 83-95 knots or 96-110 mph and/or


• Lowest Surface Pressure: 965-979 mb or 28.50-28.91 in. Hg and/or


• Storm Surge: 6 to 8 feet above normal


• Category 3
• Maximum Wind: 96-113 knots or 111-130 mph and/or


• Lowest Surface Pressure: 945-964 mb or 27.91-28.47 in. Hg and/or


• Storm Surge: 9 to 12 feet above normal


• Category 4
• Maximum Wind: 114-135 knots or 131-155 mph and/or


• Lowest Surface Pressure: 920-944 mb or 27.17-27.88 in. Hg and/or


• Storm Surge: 13 to 18 feet above normal


• Category 5
• Maximum Wind: greater than 135 knots or 155 mph and/or


• Lowest Surface Pressure: below 920 mb or 27.17 in. Hg and/or


• Storm Surge: greater than 18 feet above normal