25 (Photo by Cecil Shillingford) Researched by Franklyn Michael Supplementary Associate, CARICAD A CYCLONE, DISTURBANCE, HURRICANE “A tropical cyclone is a generic term for a lowpressure system that formed over tropical waters (25°S to 25°N) with thunderstorm activity near the center of its closed, cyclonic winds. Tropical cyclones derive their energy from vertical temperature differences, are symmetrical, and have a warm core. If it lacks a closed circulation, it is called a tropical disturbance. If it has a closed circulation but under 39 mph (34 knots, or 17 metres per second) maximum sustained surface winds, it is called a tropical depression. When winds exceed that threshold, it becomes a tropical storm and is given a name. Once winds exceed 74 mph (64 knots, 33 metres per second) it will be designated a hurricane (in the Atlantic or East Pacific Oceans) or a typhoon (in the northern West Pacific).” Tropical Disturbances -> Tropical Depressions -> Tropical Storms -> Hurricane or Typhoon. SOURCE: National Oceanographic and Atmospheric Administration References: Holland, G.J. (1993): “Ready Reckoner” – Chapter 9, Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland Neumann, C.J. (1993): “Global Overview” – Chapter 1″ Global Guide to Tropical Cyclone Forecasting, WMO/TC-No. 560, Report No. TCP-31, World Meteorological Organization; Geneva, Switzerland UTC TIME, GMT, Z TIME “What is UTC time?”, or “what is GMT time?”, or “What is Z time?”, the answer is they are time schemes. Universal Time Coordinated (UTC) used to be Greenwich Mean Time and Zulu Time (Z). This is the time at the Prime Meridian given in hours and minutes on a 24-hour clock. Most satellite pictures will give the time code next to the time taken with a UTC, GMT, or Z, but they are the same time zone. The conversion table for local times can be found below. On most satellite pictures and radar images the time will be given. If it’s not in local time then it will usually be given as UTC, GMT, or Z time. To convert this to your local time it is necessary to subtract the appropriate number of hours for the Western Hemisphere or add the correct number of hours for the Eastern Hemisphere. And don’t forget the extra hour adjustment for Daylight Savings Time or Winter Time over Standard Time for your zone. Local Time Zone Atlantic Daylight Time (ADT) Atlantic Standard Time (AST) Eastern Daylight Time (EDT) Time Adjustment (hours) -3 -4 SOURCE: National Oceanographic and Atmospheric Administration A STORM SURGE Along the coast, storm surge is often the greatest threat to life and property from a hurricane. In the past, large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina (2005) is a prime example of the damage and devastation that can be caused by surge. At least 1,500 people lost their lives during Katrina and many of those deaths occurred directly, or indirectly, as a result of storm surge. Storm Surge vs. Storm Tide Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases. (Credit: National Oceanic and Atmospheric Administration - NOAA) Storm Surge vs. Storm Tide Factors Impacting Surge — Storm surge is produced by water being pushed toward the shore by the force of the winds moving cyclonically around the storm. The impact on surge of the low pressure associated with intense storms is minimal in comparison to the • Continues on next page
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