The International Tornado Intensity Scale
Tornado Intensity  Description Of Tornado & Windspeeds  Description Of Damage (for guidance only) 

T0 
Light Tornado 17  24 m s1 (39  54 mi h1) 

T1 
Mild Tornado 25  32 m s1 (55  72 mi h1) 

T2 
Moderate Tornado 33  41 m s1 (73  92 mi h1) 

T3 
Strong Tornado 42  51 m s1 (93  114 mi h1) 

T4 
Severe Tornado 52  61 m s1 (115  136 mi h1) 

T5 
Intense Tornado 62  72 m s1 (137  160 mi h1) 

T6 
ModeratelyDevastating Tornado 73  83 m s1 (161  186 mi h1) 

T7 
StronglyDevastating Tornado 84  95 m s1 (187  212 mi h1) 

T8 
SeverelyDevastating Tornado 96  107 m s1 (213  240 mi h1) 

T9 
IntenselyDevastating Tornado 108  120 m s1 (241  269 mi h1) 

T10 
Super Tornado 121  134 m s1 (270  299 mi h1) 

Tornadoes of strength T0, T1, T2, T3 are termed weak tornadoes. Because the Tornado Scale is openended, it can be extended beyond T10 using the formulae below where v = wind velocity, T = Tornado Intensity number, and B = Beaufort Force number. v = 2.365 (T+4)^1.5 metres per second v = 8.511 (T+4)^1.5 kilometres per hour. v = 5.289 (T+4)^1.5 miles per hour v = 4.596 (T+4)^1.5 knots. Thus, B = 2 (T + 4) and T = (B/2 – 4). About the T Scale Dr. G. Terence Meaden devised The International Tornado Intensity Scale in 1972 to categorize wind speeds of tornadoes. The scale is directly related to the Beaufort Scale and is the only true tornado intensity scale with a sound scientific base. For information on the origins of the Tscale and how it was
devised visit the Tscale Origin
page. The scale allows a tornado's wind speed to be determined by various means:
Few anemometers have survived even the weakest tornado to record a peak gust and few engineering studies of tornado damage have been made. Furthermore not many observers have been close enough for Doppler measurement. Consequently most ratings are derived from the least accurate method of a nonengineering based study of damage. Nevertheless, it is important to note that the International Tornado Intensity Scale based on sound scientific formulae allows tornadic winds to be rated even if a tornado has no opportunity to cause damage (as when crossing open countryside for instance). Thus the TORRO SCALE is a true tornado wind speed intensity scale rather than purely a damage scale. The T Scale is precise. It is wellsuited for the more accurate methods of tornadic wind speed determination and also for rating weak tornadoes which account for the vast majority of global events. It is relatively easy for a basic nonengineering study of damage to produce a reasonably accurate rating of damage caused by a weak tornado because the wind speeds are relatively low. Conversely, rating strong tornadoes becomes harder and the precise nature of the scale makes the accurate rating of violent tornadoes by viewing the damage caused particularly difficult. To reduce this, adjacent points on the scale can be grouped together – thus T56 is acceptable as a rating. A tornado is only rated T0 if it passes over vulnerable objects, which are not damaged (leaving aside the more accurate methods of determining wind speeds in this instance). If a tornado is known to have occurred but details of damage or other rating information are not forthcoming, then the tornado is not given an intensity rating. Whenever information is available to provide an intensity rating, the qualifying value is the one corresponding to the tornado at its most intense. Care is given to the rating of slowmoving tornadoes, because they will create more intense damage than a fastermoving tornado of the same wind speed. In such cases, if there is no other information available to give an intensity rating, the scale number to be used will be lower than what usually corresponds to the observed damage. As a true wind speed scale, the T–SCALE can be applied to determine any wind speed, whether the wind is tornadic or not. 