Before you can plan and prepare for a hurricane, you really need to have a basic working knowledge of exactly what it is you are up against. People think they know by what they have seen on TV and have read about in books. The reality is often far different. Our first lesson in hurricane preparedness will deal with the hazards that all hurricanes pose. Remember, all hurricanes are dangerous and all have the potential for great loss of life given the right conditions. It is also important to remember that all hurricanes are NOT the same and that each must be taken seriously. Hurricanes are the strongest form of what is termed a tropical cyclone. This term is the general definition given to all tropical depressions, tropical storms and hurricanes- no matter the category. Most hurricanes begin their lives as rather tranquil but typically organized weather disturbances over the tropical regions of our oceans. All tropical cyclones need warm ocean water to survive. The minimum temperature is around 80 degrees F but this can vary depending on several complicated factors. For our learning process here, we'll stick to the typical 80 degree threshold. A good many hurricanes get their start from tropical waves of low atmospheric pressure that travel from east to west across the Atlantic Ocean. These impulses of energy begin over Africa as strong thunderstorm complexes with a surface low often associated with them. Once these waves of low pressure reach the Atlantic, they have a small chance of developing. Some develop close to the coast of Africa and track westward for several days before turning north. It is when that turn takes place that determines who gets hit by hurricanes and who does not. Most tropical waves will fizzle out or become absorbed within other weather systems- never amounting to anything more than a blob of clouds. For those that do develop, their chances of becoming a hurricane depends on several key additional factors. We know by now that hurricanes need at least 80 degree water temperatures to thrive. In addition to the warm ocean water, a developing hurricane needs the following set of ingredients to not only be in place, but also to persist over more than just a few hours. The longer these favorable conditions are present, the stronger a hurricane can become: Light winds in the atmosphere with height This is also known as low vertical wind shear. A hurricane must have deep thunderstorms, or convection, in order to lower the air pressure. The air that is rising needs to do so as vertical as possible. If strong winds in the middle and upper levels of the atmosphere blow too strong then these thunderstorms get pushed or blown off and away from the developing center (see diagram). Think of it like when you blow out a birthday candle- if you blow hard enough, the flame is extinguished. If the shear is too strong, a tropical cyclone will never have a chance to become a hurricane. On the other hand, very light vertical shear allows for extremely efficient thunderstorm growth and thus a tropical storm can strengthen quickly in to a hurricane and so forth. This was the case over and over again during the historic 2005 hurricane season as conditions in the upper atmosphere were ideal for hurricanes like Dennis, Katrina, Rita and Wilma to form and become record-setting events. Moist, unstable air in the mid-levels Nothing seems to stop a growing hurricane quicker than dry air. We say "dry" since it is relative to the super-juicy air that creates hurricanes in the first place. Hurricanes need air that is rich with moisture and thus stored heat energy. When a weather system injects air with lower dewpoints and humidity in to a hurricane, it saps the intensity and in a hurry. Another example of this is your bathroom. Take a steamed up mirror and turn on the hair-drier. That air is warmer and drier than the air that created the steam-bath on your mirror. This drier air evaporates the moisture that has collected on the glass- clearing it up. While the relationship is not perfect, this is similar to what happens when dry air becomes involved with a tropical cyclone of any strength. This dry air can come from many sources: Africa (also associated with dust outbreaks- click here for excellent example), land masses that border the oceans, upper level weather systems and air masses that come south out of Canada. No matter the source, dry air and hurricanes do not mix and the dry air seems to win out more often than not. Outflow established at upper levels A hurricane is a heat engine. Warm, moist air spirals in from the outer rain bands towards the eye. Within the core, the air rises rapidly and gets thrown out at the top near the stratosphere. This exhaust is called outflow. If this process is effecient enough, it couples with the explosive thunderstorm development and creates a chain-reaction that ultimately leads to a powerful hurricane. There are many ways to establish these outflow channels, as they are often called, but if they get cut off or strong winds impede this process, a hurricane can literally choke and weaken. Outflow is mentioned extensively on the National Hurricane Center Forecast Discussions. It's quite simple: the better the outflow is established, the more potential exists for the hurricane to intensify. Even if all of these necessary ingredients are in place, we do not always get a hurricane from the tropical disturbances that dot the Atlantic each year. There are other less understood factors that ultimately lead to the development of the these powerful weather systems. Once we do have a hurricane on the map, a system of tracking tools is available for nearly constant information to flow concerning the track and intensity. This begins with advanced weather satellites that provide our first line of defense against an impending hurricane threat. Hurricane Tracking Satellites are indeed our early warning mechanisms for detecting hurricanes before they are ever a threat to land. Geostationary satellites, part of the GOES series, provide imagery several times per hour over the main hurricane and other tropical cyclone regions of the Atlantic and Pacific. For monitoring potential seedling storms over Africa, we utilize the Meteosat satellite to track tropical waves before they move in to the Atlantic. The most common satellite views are visible and infrared. A visible satellite image is almost exactly what it sounds like- a real view from space as if you were there taking the photo yourself. These images work well during the daylight hours for obvious reasons. Visible satellite imagery can help to detect a poorly defined center in a weak or developing tropical cyclone and can provide spectacular views of the menacing eye of a well formed, intense hurricane. An infrared (IR) satellite image shows us degrees of heat, so to speak. There are a variety of colors used to distinguish between the warmer areas of the satellite picture and the colder areas. As a rule of thumb, the higher the clouds are in the atmosphere, the colder they will be. IR satellite imagery shows us these temperatures very well. Why is cloud height and temperature important? Because the taller the tropical thunderstorms (also known as convection) reach in to the atmosphere, the stronger the updrafts or upward motion is. This intense convection is a tell-tale sign of a strong or strenthening tropical cyclone.