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Institute for Crisis, Disaster, and Risk Management Crisis and Emergency Management Newsletter Website |
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October
2008
Volume
15
- Number 1 |
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Tracking the Path of a Hurricane by Cynthia Tara Ferguson The National Hurricane Center (NHC) has been issuing hurricane predictions since 1954. The NHC forecast models assist in the prediction of future hurricane events. Tracking both the path and the intensity of a hurricane involves utilizing more than just one hurricane forecast model. In reality, the National Hurricane Center (NHC) makes use of a variety of models. These forecast models, derived from mathematical computations, can be run using several types of computers, super-computers and computer programs. There are five basic types of models: Statistical, Statistical-Dynamical, Dynamical, Ensemble and Trajectory. Some models are considered Early Models, while others are categorized as Late Models. The difference between the two is whether they are available to the forecaster during the contemporary forecast cycle. During hurricane forecasts, weather channels frequently show sets of colored lines on the weather screen, which are collectively called a “spaghetti model”. Each colored line has a set of initials attached to it, which represents the particular model making the tracking and/or intensity prediction. Statistical models make predictions using relationships between storm-specific information. This information includes: location and time of year, and the behavior of historical storms. Statistical models are among the quickest to run and are typically available to forecasters within minutes of initialization. One example of this model type is the Climatology and Persistence Model (CLIPER5), which can provide up to a 5 day forecast. Dynamical models solve the physical equations of motion governing the atmosphere. Examples of this type of model include: the U.S. National Weather Service Global Forecast System (GFS) and the Navy Operational Global Atmospheric Prediction System (NOGAPS). Statistical- Dynamical models are based on historical relationships between storm behavior and storm-specific details such as location and date use both dynamical and statistical techniques. Examples of this type of model include: NHC91 (Pacific) /NHC98 (Atlantic) Models and the Statistical Hurricane Intensity Prediction Scheme (SHIPS). Ensemble forecasts are based on a combination of forecasts from a number of models which are often called “Consensus Models”. These models are not true forecast models, but compilations of forecasts from other models. The most commonly used consensus forecasts used by the NHC are the GUNA, CONU and the FSSE. Trajectory models project the path of a tropical cyclone (TC) based on the prevailing flow derived from a separate dynamical model. An example of a Trajectory model is the Beta and Advection Model (BAM). Spaghetti forecast models also utilize the input of personnel who have years of professional training and experience in order to make the best predictions of hurricane trajectories. The National Hurricane Center (NHC) official forecasts generally have smaller errors than other individual models because a given NHC forecast does not rely solely on any one individual model (i.e. "model of the day" or "best model"). Instead the NHC forecasts utilize all available model guidance as well as forecaster experience. Because of this, users should consult the official forecast products issued by the NHC and local National Weather Service Forecast Offices, and also understand that forecasts include a certain degree of uncertainty. NHC provides forecasts based on probability, which can assist with evaluating forecast uncertainty. In addition, the NHC provides detailed information on the accuracy of its previous forecasts with a yearly verification report. Useful Websites: Atlantic Oceanographic and Meteorological Laboratory (Hurricane Research Division): http://www.aoml.noaa.gov/hrd/abouthrd.htm References Landsea, C. and Laurent, A. (2008) Hurricane tracker debuts in time to study Gustav. Government Executive.com. Retrieved on 21 September, 2008 from: http://www.govexec.com/dailyfed/0908/090408l1.htm
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