The well-known Cuban meteorologist Elier Pila has shared with his followers on Telegram some interesting details about the trajectory cone and the forecast models of a cyclonic system. This explanation is very useful to understand some aspects related to Tropical Depression number 9 of the current season, which could become a tropical cyclone with a possible trajectory over Cuba.
Below we share the text published by the specialist:
What happens to the cone? How is built?
The cone is a revised information made by specialists, in this case the National Hurricane Center, which does contain the forecast of this center and constitutes an official forecast.
It is based on a central path on which the cone is built. The 2/3 error in the forecasts in the last 5 years is taken as a base, for each one of the terms: 12, 24, 48 hours, as well as up to 5 days (120 hours). With that error, an imaginary circle centered on the predicted point is drawn and the edges of that circle are joined with the figure of the cone.
But here there is an important detail, we are talking about circles, a circumference means that there is a certain error with respect to that central point, but not only “sideways” but also forwards or backwards in the trajectory. Normally people do not see this detail, because these imaginary circles do not appear and only the outer edge of the cone is visible. This error takes into account the delay or advance that there may be with respect to the forecast and this is also very important.
The cone and its opening
The cone does not indicate the real uncertainty in the forecast, the opening of the cone will always be the same because it is based on a fixed error. It is also very important that, especially in the initial stages, where the cone is small, people only pay attention to whether the center (what is forecast) is going to pass through their area of interest. Even in a perfect forecast, dangerous phenomena related to wind, sea and rain will occur outside the cone area, even in areas very far from the center of circulation
Here is the importance of knowing something about these graphics because they are going to become more visible and common, especially when there are dangerous situations.
It is good to know them, because although they appear published in official information and explained by specialists in the media, many times they are also shared by people who are not specialists or do not fully know them, and any user can go to consult this information individual.
And in each of these cases it helps to have a better idea of what they are seeing. Always remind them that any decision to be made regarding this type of information should always be based on official information and not on any type of model forecast.
Other examples of ensemble-type models. The trajectory in black is the average, not the most likely or safe.