From: Weather Nation
by Meteorologist Craig Setzer
At WeatherNation we believe discussions are healthy. Sometimes the best ideas are born from exchanging opinions.
Today, guest blogger WFOR CBS4 Meteorologist Craig Setzer offers his thoughts on “the 5 day cone”. We would love to hear what you think.
Take it away, Craig:
From time to time I get on a little rant about the weather or some facet of it. Today I’m happy to rant about “the 5 day cone”. Some call it the “uncertainty cone”, others call it the “cone of fear”, whatever you call it, I think it has outlived its usefulness. Or at a minimum, it needs to be replaced with something more descriptive of the true effects from a tropical cyclone.
First, let’s talk about what the cone is. It is a polygon, representing the track forecast error for the previous 5 years, where two thirds of the time the center of a tropical cyclone is expected to remain. That’s right, about 33% of the time, the center may move outside of the cone during the five day forecast time frame. The National Hurricane Center has improved their track forecasting skill, and reduced the error in forecast points tremendously since the 1990s when the cone first started getting used. The size of the cone is now half of what it was two decades ago. But the cone only tells us one thing, where the center of the tropical depression, tropical storm, or hurricane should be. The cone tells us nothing about the size of the storm, the intensity of the storm, the hurricane specialist’s confidence of his track forecast, or where the worst weather will be. Too often people see the cone as a line that separates tropical storm verses breezy showers and that’s simply not the case.
|Source: CIMMS, Univ of Wisconsin|
Tropical storm Karen is a perfect example of the failure of the cone. The storm is highly asymmetric (lopsided), with heavy thunderstorms and the strongest winds 100 miles or more east of the center of circulation. That’s right, the worst weather is not anywhere near the cone. The weather in and near the cone is partly cloudy and fairly breezy. And because the shear is expected to remain high enough to keep the cyclone highly lopsided, the worst weather may not ever be inside of the cone.
So what do we replace the cone with? The National Hurricane Center has been generating Wind Speed Probability (WSP) graphics for some time now. These graphics incorporate the storms wind field, strength, and uncertainty. They more accurately represent the areas that could experience the worst of the weather from a tropical storm or hurricane. And these colored risk areas change based on the storm’s forecast size and intensity, unlike the cone which is always the same size, no matter what the storm is doing or how big it gets.
The time of the cone has passed. The public should be weaned off this archaic graphic and given something more representative of what their true threat is from a tropical cyclone.