A tropical disturbance is any persistent area of thunderstorms that forecasters can track for several days in satellite pictures. When such a system develops a closed cyclonic circulation (south wind on the east side, east wind on the north, north wind on the west and, hardest to find, west winds south of the center) it becomes a depression and is numbered. When the maximum winds reach 35 kt, often with pressures still above 1000 mb, it becomes a tropical storm and receives a name. When it reaches 65 kt (74 mph) it is a hurricane. Hurricanes are classified by intensity into five categories:
Category | Pressure (hPa)
| Wind (mph) | Damage
| ONE | above 980 | 74 to 85 | Minimal
| TWO | 979 to 965 | 86 to 110 | Moderate
| THREE | 964 to 945 | 111 to 130 | Extensive
| FOUR | 944 to 920 | 131 to 155 | Extreme
| FIVE | below 920 | more than 155 | Catastrophic
| |