GRAND TURK, Turks and Caicos Islands; Monday, August 17th, 2009 – The Department of Disaster Management and Emergencies (DDME) would like to inform the general public on how a Hurricane, Tropical Disturbance, Tropical Depression and Tropical Storm is classified and how to understand the advisory categorization.
Hurricanes are tropical cyclones – storms that rotate counterclockwise with wind spends in excess of 74 miles per hour (MHP) or (64 knots). Most hurricanes form over warm seas near the equator. They are created when the sun heats the ocean surface, causing heated water vapor to rise, condense and form clouds. These clouds begin to spiral as the earth rotates. More air is pulled underneath and a large vortex is formed.
As the hurricane moves forward, its right front quadrant is typically where the most devastation occurs. Over land, hurricanes lose their strength, as the heated water that sustains it is no longer able to support it.
CLASSIFYING HURRICANES:
Tropical Disturbance: A rotary circulation in the upper atmosphere that produces little to no effect on the surface.
Tropical Depression: A low-pressure area hat produces some rotary circulation on the ocean’s surface. Tropical depressions sustain wind speeds of less than 39mph.
Tropical Storm: A low-pressure area with a distinct rotary circulation with wind speeds from 39-73 mph
Hurricane: A low-pressure area with a pronounced rotary circulation. Hurricane wind speeds are at least 74mph and can on rare occasions reach up to 200mph. Many hurricanes measure 300 miles across, but they have been known to span a 600-mile diameter.
CATEGORIZING A HURRICANE’S STRENGTH
The Saffir/Simpson Hurricane Scale is used internationally to determine a hurricane’s strength and predict the amount of damage it might cause. This is predicted as follows:
Category 1 Wind speed: 74-95 mph Minimal damage
Category 2 Wind speed: 96-110 mph Moderate damage
Category 3 Wind speed: 111-130 mph Major damage
Category 4 Wind speed: 131-155 Severe damage
Category 5 Wind speed: 156 + mph Catastrophic damage
UNDERSTANDING TROPICAL CYCLONE ADVISORY NOTICES
There are 3 types of advisory notices provided by the National Hurricane Centre, and they are as follows:
- Routine Advisory: Information regarding tropical cyclones (tropical depressions, tropical storms or hurricanes) is updated every 6 hours.
- Special Advisory: An unscheduled advisory given whenever there of a significant change in the status of the cyclone.
- Intermediate Advisory: A scheduled public advisory that provides updated information every 2 or 3 hours.
ADVISORIES
Advisories warn us of impending danger from severe weather. Here are the specific advisories to note during hurricane season.
Tropical Storm Watch: Wind speeds of 39-73 mph are expected within 36 hours.
Tropical Storm Warning: Wind speeds of 39-73 mph are expected within 24 hours.
Hurricane Watch: Wind speeds of 7 mph or higher are expected within 36 hours.
Hurricane Warning: Wind speeds of 74 mph or higher are expected within 24 hours.
The Department of Disaster Management and Emergencies will continue to monitor and update the publics of any all hurricane systems as the situation demands.
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