Tropical Cyclones are among nature's most powerful and destructive phenomena. If you live in an area prone to tropical cycles you need to be prepared. Even areas well away from the coastline can be threatened by destructive winds, tornadoes and flooding from these storms. How great is the danger? For 1970-2010, the average numbers per year were as follows: 11 tropical storms, 6 of which became hurricanes. Over a typical 2-year period, the U.S. coastline is struck by an average of 3 hurricanes, 1 of which is classified as a major hurricane.
While hurricanes pose the greatest threat to life and property, tropical storms and depressions can be devastating. Floods from heavy rains and severe weather, such as tornadoes, can cause extensive damage and loss of life. For example, Tropical Storm Allison produced over 40 inches of rain the the Houston area in 2001, causing about $5 billion in damage and taking the lives of 41 people.
Tropical cyclones forming between 5 and 30 degrees North latitude typically move toward the west. Sometimes the winds in the middle and upper levels of the atmosphere change and steer the cyclone toward the north and northwest. When tropical cyclones reach latitude near 30 degrees North, they open move northeast. Hurricane seasons and their peaks for Florida are from June 1 to November 30 with the peak being in mid-August to late October.
The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane's sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. Category 1 and 2 storms are still dangerous, however, and require preventative measures.
Storm surge and large waves produced by hurricanes pose the greatest threat to life and property along the coast.
STORM SURGE is an abnormal rise of water generated by a storm's winds. Storm surge can reach heights well over 20 feet and can span hundreds of miles of coastline. In the northern hemisphere, the hemisphere, the highest sure values typically occur in the right front quadrant of a hurricane coincident with onshore flow; in the southern hemisphere, the left front quadrant. More intense and larger hurricanes produce higher surge. In addition, shallower offshore waters contribute to higher storm surge inundation. Storm surge is by far the greatest threat to life and property along the immediate coast.
STORM TIDE is the water level rise during a storm due to the combination of storm surge and the astronomical tide. For example, if a hurricane moves ashore at a high tide of 2 feet, a 15 food surge would be added to the high tide, creating a storm tide of 7 feet. The combination of high winds and storm tide topped with battering waves can be deadly and cause tremendous property damage along an area of coastline hundreds of miles wide.
The destructive power of storm surge and large battering waves can result in loss of life, buildings, destroyed, beach and dune erosion and road and bridge damage along the coast. Storm surge can travel several miles inland. In estuaries and bayous, salt water intrusion endangers public health and the environment.
Hurricanes and tropical storms can also produce tornadoes. These tornadoes most often occur in thunderstorms embedded in rain bands well away form the center of the hurricane; however, they can also occur near the eyewall. Usually, tornadoes produced by tropical cyclones are relatively weak and short-lived, but they pose a significant threat.
Hurricane-force winds, 74 mph or more, can destroy buildings and mobile homes. Debris, such as signs, roofing material, siding and small items left outside become flying missiles during hurricanes. Winds can stay above hurricane strength well inland. In 2004, Hurricane Charley made landfall at Punta Gorda on the southwest Florida coast and produced major damage well inland across central Florida with gusts of more than 100 mph.
Tropical cyclones often produce widespread, torrential rains in exceeds of 6 inches, which may result in deadly and destructive floods. In fact, flooding is the major threat from tropical cyclones for people living inland. Flash flooding, defined as a rapid rise in water levels, can occur quickly due to intense rainfall. Longer term flooding on rivers and streams can persist for several days after the storm.
Rainfall amounts are not directly related to the strength of tropical cyclones but rather to the speed and size of the storm, as well as the geography of the area. Slower moving and larger storms produce more rainfall. In addition, mountainous terrain enhances rainfall from a tropical cyclone.
The strong winds of a tropical cyclone can cause dangerous waves that pose a significant hazard to mariners and coastal residents and visitors. When the wave break along the coast, they can produce deadly rip currents--even at large distances from the storm.
Rip currents are channeled currents of water flowing away from shore, usually extending past the line of breaking waves, that can pull even the strongest swimmers away from shore. In 2008, despite the fact that Hurricane Bertha was more than 1,000 miles offshore, the storm resulted in rip currents that killed three people along the New Jersey coast and required 1,500 lifeguard rescues in Ocean City, Maryland, over a 1 week period.
In 2009, all six deaths in the United States directly attributable to tropical cyclones occurred as the result of drowning from large waves or strong rip currents.
The National Weather Service (NWS) continuously broadcasts warning, watches, forecasts and non-weather related hazard information on NOAA Weather Radio All Hazards (NWR). The average range of the 1000+NWR transmitters is 40 miles, depending on topography. For the best performing NWR receivers, NWS suggests you look at devices certified to Public Alert (TM) standards.
These radios meet specific technical standards and come with many features such as Specific Area Message Encoding (SAME), a battery backup, both audio and visual alarms, selective programming for the types of hazards you want to be warned for, and the ability to activate external alarm devices for people with disabilities. Similar to a smoke detector, a NWR can wake you up in the middle of the night to alert you of a dangerous situation.