 In a developing cyclone , the technique takes advantage of the fact that cyclones of similar intensity tend to have certain characteristic features , and as they strengthen , they tend to change in appearance in a predictable manner . The structure and organization of the tropical cyclone are tracked over 24 hours to determine if the storm has weakened , maintained its intensity , or strengthened . Various central cloud and banding features are compared with <unk> that show typical storm patterns and their associated intensity . If infrared satellite imagery is available for a cyclone with a visible eye pattern , then the technique utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops to determine intensity ( colder cloud tops generally indicate a more intense storm ) . In each case a " T @-@ number " ( an abbreviation for Tropical Number ) and a Current <unk> ( <unk> ) value are assigned to the storm . These measurements range between 1 ( minimum intensity ) and 8 ( maximum intensity ) . The T @-@ number and <unk> value are the same except for weakening storms , in which case the <unk> is higher . For weakening systems , the <unk> is held as the tropical cyclone intensity for 12 hours , though research from the National Hurricane Center indicates that six hours is more reasonable . The table at right shows the approximate surface wind speed and sea level pressure that corresponds to a given T @-@ number . The amount a tropical cyclone can change in strength per 24 ‑ hour period is limited to 2 @.@ 5 T @-@ numbers per day . 
