TROPICAL CYCLONE HAZARDS
By Kerry N. Mallory, AE5JY
The Four Primary Weapons of a Tropical Cyclone are:
- Storm Surge
- Rain/Freshwater Flooding
- Tornadoes/Downbursts/Straight Line Winds
Tropical Depressions have maximum sustained winds of 38mph or less.
Tropical Storms maximum sustained winds are 39-73mph.
Hurricanes maximum sustained winds are 74mph or greater.
Tropical Storm force winds can be felt hundreds of miles from the Eye of a Hurricane and can cause significant damage to trees and roofs. Wind can cause damage to power lines and are the primary cause of power outages and interruptions as a storm approaches.
Saffir-Simpson Hurricane Wind Scale
Category Wind (mph) Potential Damage
1 74-95 Very dangerous winds will provide some damage
2 96-110 Extremely dangerous winds will cause extensive damage
3 111-129 Devastating damage will occur
4 130-156 Catastrophic damage will occur
5 >156 Catastrophic damage will occur
An abnormal rise in sea level accompanying a hurricane or other intense storm and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge can cause coastline and inland flooding as well as significant damage to homes and businesses. Large Tropical Storms or Hurricanes in the Gulf of Mexico can meander for several days in the Gulf before proceeding to make landfall. They have the ability to significantly increase Storm Surge by the inherent design of The Gulf of Mexico.
Unlike the Atlantic, which allows Storm Surge to dissipate further down the coastline, the Gulf of Mexico focuses more storm surge into affected areas. Storm surge is also responsible for an increase in dangerous rip tides making coastal waters extremely dangerous for swimmers. Storm Surge can affect other areas well outside the immediate coastal area as the water surge can travel up rivers and tributaries causing widespread flooding.
Rain and Freshwater Flooding
Rain can accumulate extremely fast in a slow moving storm. In June of 2001, Tropical Storm (TS) Allison
dropped 38.6 inches of rain in the Houston area over a 6 day period. TS Allison killed 41 people, 27 of which drowned. Although TS Allison is most often remembered for the widespread flooding and devastation it brought to Harris County/Houston, Areas of LA, MS, and GA experienced rainfall amounts of 10+ inches and extensive flood damage as well. Remember a Tropical Storm or a Hurricane is NOT just a point on a map.
Tornadoes/Downbursts/Straight Line Winds
Tornadoes, Downbursts and Straight Line wind are typical characteristics of Tropical Cyclones. Even a tropical depression can bring high gusty winds and possibly a few tornadoes. Tornadoes can form far away from the eye of a Tropical Storm or Hurricane. Always pay close attention to how far tropical storm winds extend from the center or the eye of approaching Tropical Storm or Hurricane.
Downbursts are caused by divergence aloft and a column of sinking air that, once it impacts the ground, can send out straight line winds that exceed 165mph. Often the damage caused by a downburst can resemble damage caused by tornadoes and experts often have to examine the damage pattern to discern the difference. Downbursts are much more frequent than tornadoes. For every 1 Tornado there are about 10 downburst damage reports. Always pay close attention to local weather reports. Doppler radar is able to look inside the thunderstorm and see the relative movement of air from reflections off of rain drops in the moving air giving the Meterologist indications of vorticity to help identify Tornadoes. Downbursts are not so easily detected which makes them deadlier in many cases than tornadoes for which speed and direction can be determined.
Know the Enemy. Make no mistake about it Tropical Storm and Hurricanes are Your Enemy.
They have an arsenal of weapons (Hazards);
Tornadoes/Downbursts/Straight Line Winds
Understand these Hazards and what they are capable of doing. Develop a good plan to mitigate the damage and protect your family.
Be Prepared so you won’t be caught off guard when tropical cyclones or hurricanes strike.
Weather Related Links
This is a good, primary list of links for weather information but there are literally hundreds of excellent weather related links online.
That concludes tonight’s training. Are there any questions, comments or suggested additions to this material?
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