Volume 1 Number 37
September 13, 2004



Chart A

Chart B
This is an experimental product

Chart C



Studying storms and getting information to the public is a 24/7 task this time of year as Ivan is approaching the Gulf of Mexico.

The Tropical Prediction Center (TPC) is a component of the National Centers for Environmental Prediction (NCEP) located at Florida International University in Miami, Florida. The TPC mission is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards. Through international agreement, the TPC has responsibility within the World Meteorological Organization to generate and coordinate tropical cyclone analysis and forecast products for twenty-four countries in the Americas, Caribbean, and for the waters of the North Atlantic Ocean, Caribbean Sea, Gulf of Mexico, and the eastern North Pacific Ocean. TPC products are distributed through a close working relationship with the media and emergency management communities.

The TPC collaborates with universities, government research laboratories, international tropical weather centers, the private sector and other National Weather Service components to maintain its leading edge in tropical meteorology through coordinated operations, research, training and forecast development techniques.

Chart A shows an approximate representation of coastal areas under a hurricane warning (red), hurricane watch (pink), tropical storm warning (blue) and tropical storm watch (yellow). The orange circle indicates the current position of the center of the tropical cyclone. The black line and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The letter inside the dot indicates the NHC's forecast intensity for that time.  

NHC forecast tracks of the center can be in error; the average track forecast errors in recent years were used to construct the areas of uncertainty for the first 3 days (solid white area) and for days 4 and 5 (white stippled area). 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. The intensity forecast chart and table below provide intensity forecast and intensity forecast uncertainty information.

It is also important to realize tropical cyclones are not a point. Their effects can span many hundreds of miles from the center. The area experiencing hurricane force (one-minute average wind speeds of at least 74 mph) and tropical storm force (one-minute average wind speeds of 39-73 mph) winds can extend well beyond the white areas shown enclosing the most likely track area of the center. The distribution of hurricane and tropical storm force winds in this tropical cyclone can be seen in the Cumulative Wind Distribution graphic displayed below.

Chart B shows the probability, in percent, that the center of the tropical cyclone will pass within 75 statute miles of a location during the 72 hours beginning at the time indicated in the caption. The caption also provides the name of the tropical cyclone and the advisory number from which the probabilities were generated. Contour levels shown are 10%, 20%, 50% and 100%.

Chart C shows how the size of the storm has changed, and the areas potentially affected so far by sustained winds of tropical storm force (in orange) and hurricane force (in red). The display is based on the wind radii contained in the set of Forecast/Advisories indicated at the top of the figure. Users are reminded that the Forecast/Advisory wind radii represent the maximum possible extent of a given wind speed within particular quadrants around the tropical cyclone. As a result, not all locations falling within the orange or red swaths will have experienced sustained tropical storm or hurricane force winds, respectively.