Atmosphere And Weather

What causes a Hurricane



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"The Anatomy of a Hurricane"

If you are a current resident of Florida you are absolutely familiar with what a hurricane is. In fact currently were witnesses to history in this 2005 Hurricane Season. This season has been the most active and dangerous hurricane season ever. We've gone through all the named storms and a good beginning of the Greek alphabet.

Hurricanes are an amazing act of nature and product of weather. This year the National Hurricane Center and local meteorologists have been earning their pay and getting little sleep in tracking and predicting these awe inspiring storms.

Hurricanes follow along paths or tracks. "The storm can be thought of as being steered by the surrounding environmental flow throughout the depth of the troposphere. The movement of hurricanes has been likened to a leaf being carried along by the currents in a stream, except that for a hurricane the stream' has no set boundaries" (Lutgens and Tarbuck p328).

One of the currently used predicting techniques that the hurricane forecasters utilize is called the Dvorak technique. This methodology estimates the intensity of the cyclone through pictures. Forecasters use this method by looking at a "current satellite picture of a tropical cyclone, then matching the image versus a number of possible pattern types: Curved band Pattern, Shear Pattern, Eye Pattern, Central Dense Overcast Pattern, Embedded Center Pattern or Central Cold Cover Pattern. If infrared satellite imagery is available for Eye Patterns then the scheme utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops. The larger the difference, the more intense the tropical cyclone is estimated to be" (Hurricane Research Division, FAQ).

With this technique winds and centralized pressure are assumed to always be consistent. "However, since the winds are really determined by the pressure gradient, small tropical cyclones (like the Atlantic's Andrew in 1992, for example) can have stronger winds for a given central pressure than a larger tropical cyclone with the same central pressure. Thus caution is urged in not blindly forcing tropical cyclones to "fit" the above pressure- wind relationships" (Hurricane Research Division, FAQ).

Measuring winds and pressure properly are important because this system is used to determine the storms intensity and ultimate damage by being placed as a category 1 5 severity. In the past hurricane prediction for landfall was one to three days out. Today more pressure is being put on meteorologists to predict up to five days out because of the evacuation of residents from the target area. History has proven that accuracy in meteorology is imperative. As an example of what meteorology is trying to prevent we can look at the unprepared residents of Galveston, Texas in September 1900 when a massive hurricane struck with little to no warning taken the lives upwards of 8000 people.

When researchers present their predictions to the people they use a spaghetti model. This is a series of tracks for an incoming hurricane and the probabilities of landfall. Using this model there is a cone of predicted landfall error. First the "NHC runs the official track of each hurricane and that should be used to protect your life and property" (House). Then they list tracks according to early-cycle, late-cycle and global tracks. The end result is what you see on the 6:00pm news. The "NHC forecast tracks of the center can be in error; the average track forecast errors in recent years was used to construct the areas of uncertainty for the first 3 days and for days 4 and 5. The historical data indicate the entire 5-day path of the center of the tropical cyclone will remain within the outer uncertainty area about 60-70% of the time. There is also uncertainty in the NHC intensity forecasts" (Tropical Storm EPSILON).

One of the most instrumental developments in hurricane tracking/predicting technology is the invention of hurricane satellites. Before satellites were put in space, planes were the best and sometimes only source of information about a hurricane's position and intensity. However, "because the tropical and subtropical regions that spawn hurricanes consist of enormous areas of open ocean, conventional observations are limited" (Lutgens and Tarbuck p329) and meteorological satellites are required to cover such extensive areas. With the use of satellites weather patterns can be tracked long before the actual development of a cyclone. The only downfall of the satellite system is that "wind speed estimates can be off by tens of kilometers per hour and this makes it impossible to determine with accuracy detailed structural characteristics" (Lutgens and Tarbuck p329).

Even though we use satellites to predict and track weather patterns forecasters still rely on hurricane hunters or aircraft reconnaissance to physically go out into the hurricane and report back more accurate and detailed information from the heart of the storm. One group in charge of this amazing task is the "53rd Weather Reconnaissance Squadron, a component of the 403rd Wing located at Keesler Air Force Base in Biloxi, Miss. This is a one-of-a-kind organization. It is the only unit in the world flying hurricanes on a routine basis" (United States Air Force Reserve Fact Sheet).

While hurricanes will cease to threaten the United States; hurricane hunters, forecasters, and meteorologists alike will cease to charge on in the predicting and tracking of these marvelous and dangerous weather formations. However, looking back over the years at technology then and now you can see the production of more lives saved and better warning systems. Today we are witnesses to history that is both beautiful and terrible. Knowing there are people out there trying to make world a safer place can give us that much more peace of mind.



Bibliography

House, . "SCI FRI: The Hurricane Cone: Understanding Spaghetti Models." 21 Oct.
2005. Daily Kos. 29 Nov. 2005
.

"Hurricane Research Division, FAQ." National Hurricane Center. 2005. NOAA. 28
Nov. 2005 .

Lutgens and Tarbuck, . The Atmosphere. 9th ed. Upper Saddle River: Prentice Hall,
2004.

"Tropical Storm EPSILON." Tropical Prediction. 29 Nov. 2005. NWC. 29 Nov. 2005 .

"United States Air Force Reserve Fact Sheet." USAF Hurricane Hunters. Oct. 1999.
05 Dec. 2005 .

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