POST-TROPICAL CYCLONE TAMMY

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Wind Speed Probabilities	Arrival Time of Winds	Wind History	Warnings/Cone Interactive Map	Warnings/Cone Static Images	Warnings and Surface Wind

Hurricane Wind Speed Probability 0 12 24 36 48 60 72 84 96 108 120 hours Loop

50-knot Wind Speed Probability 0 12 24 36 48 60 72 84 96 108 120 hours Loop

Tropical Storm Wind Speed Probability 0 12 24 36 48 60 72 84 96 108 120 hours Loop

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Download 120-h GIS data: 5 km .shp  0.5 degree .shp

About this product:

Note: The time of the tropical cyclone's center location at the bottom of the graphic will be 3 hours earlier than the time of the current advisory. The forecast cycle for each advisory begins 3 hours prior to the issuance of the advisory products.

These graphics show probabilities of sustained (1-minute average) surface wind speeds equal to or exceeding 50 kt (58 mph). These wind speed probability graphics are based on the official National Hurricane Center (NHC) track, intensity, and wind radii forecasts, and on NHC forecast error statistics for those forecast variables during recent years. Each graphic provides cumulative probabilities that wind speeds of at least 58 mph will occur during cumulative time periods at each specific point on the map. The cumulative periods begin at the start of the forecast period and extend through the entire 5-day forecast period at cumulative 12-hour intervals (i.e., 0-12 h, 0-24 h, 0-36 h, ... , 0-120 h). An individual graphic is produced for each cumulative interval, and the capability to zoom and animate through the periods is provided. To assess the overall risk of experiencing winds of at least 58 mph at any location, the 120-h graphics are recommended.

These probabilities will be updated by the NHC with each advisory package for all active tropical cyclones in the Atlantic and eastern North Pacific basins. While separate graphics are focused on each individual tropical cyclone, probabilities resulting from more than one active tropical cyclone may be seen on each graphic.

It is important for users to realize that wind speed probabilities that might seem relatively small at their location might still be quite significant, since they indicate that there is a chance that a damaging or even extreme event could occur that warrants preparations to protect lives and property.

Additionally, these probability products are available on the National Weather Service's National Digital Forecast Database (NDFD) graphical tropical webpage.

Coastal Watches/Warnings and Forecast Cone for Storm Center

Forecast Length*	Forecast Track Line	Initial Wind Field
Full Forecast 3 days	On Off	On Off

* If the storm is forecast to dissipate within 3 days, the "Full Forecast" and "3 day" graphic will be identical

Click Here for a 5-day Cone Printer Friendly Graphic

How to use the cone graphic (video):

About this product:

This graphic 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, when selected, and dots show the National Hurricane Center (NHC) forecast track of the center at the times indicated. The dot indicating the forecast center location will be black if the cyclone is forecast to be tropical and will be white with a black outline if the cyclone is forecast to be extratropical. If only an L is displayed, then the system is forecast to be a remnant low. The letter inside the dot indicates the NHC's forecast intensity for that time:

D: Tropical Depression – wind speed less than 39 MPH
S: Tropical Storm – wind speed between 39 MPH and 73 MPH
H: Hurricane – wind speed between 74 MPH and 110 MPH
M: Major Hurricane – wind speed greater than 110 MPH

NHC tropical cyclone forecast tracks can be in error. This forecast uncertainty is conveyed by the track forecast "cone", the solid white and stippled white areas in the graphic. The solid white area depicts the track forecast uncertainty for days 1-3 of the forecast, while the stippled area depicts the uncertainty on days 4-5. Historical data indicate that the entire 5-day path of the center of the tropical cyclone will remain within the cone about 60-70% of the time. To form the cone, a set of imaginary circles are placed along the forecast track at the 12, 24, 36, 48, 72, 96, and 120 h positions, where the size of each circle is set so that it encloses 67% of the previous five years official forecast errors. The cone is then formed by smoothly connecting the area swept out by the set of circles.

It is also important to realize that a tropical cyclone is 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 Wind History graphic linked above.

Considering the combined forecast uncertainties in track, intensity, and size, the chances that any particular location will experience winds of 34 kt (tropical storm force), 50 kt, or 64 kt (hurricane force) from this tropical cyclone are presented in tabular form for selected locations and forecast positions. This information is also presented in graphical form for the 34 kt, 50 kt, and 64 kt thresholds.

Note:  A detailed definition of the NHC track forecast cone is also available.