A tropical wave or easterly wave defined as a cluster of clouds and thunderstorms moving through the tropics.
When the tropical wave develops a rotary, cyclonic circulation with sustained winds to 38 miles per hour.
Once winds within a tropical system reach 39 miles per hour and the distinct low-pressure area is well defined by a rotating circulation, the system is considered a tropical storm and is given a name.
A hurricane has sustained winds exceeding 74 miles per hour or greater, dangerously high water and rough seas. Hurricanes are categorized by severity using the Saffir-Simpson Hurricane Wind Scale:
Saffir-Simpson Hurricane Wind Scale
Category One Winds 74 to 95 miles per hour.
Category Two Winds 96 to 110 miles per hour.
Category Three Winds 111 to 129 miles per hour.
Category Four Winds 130 to 156 miles per hour.
Category Five Winds 157 miles per hour.
Actual storm surge values will vary considerably depending on coastal configurations and other factors.
Watches & Warnings
When a tropical storm or hurricane threatens, the National Hurricane Center will issue advisories based on the projected time until landfall of the storm.
A tropical storm or hurricane watch means that tropical storm or hurricane conditions pose a possible threat in a specified region within 36 hours. You should begin preliminary preparations. Stay tuned to local news or the weather channel for updates.
A tropical storm or hurricane warning means that tropical storm or hurricane conditions are expected in a specified region within 24 hours. All preparations should be completed. Stay tuned to local news or the weather channel for evacuation orders and additional instructions.
Municipal Emergency Operations Center Operating Conditions
Day-to-day operations to include normal training and exercises.
Disaster or emergency situation likely or imminent. Full or partial activation of the City of Charleston Municipal Emergency Operations Center.
Disaster or emergency situation in effect; full-fledged emergency response operations on-going; the highest state of emergency operations. Full activation of the City of Charleston Municipal Emergency Operations Center.