Uncertainty is a fundamental characteristic of tropical cyclone forecasting. The current track forecast of the center of Tropical Storm Ernesto and the uncertainty associated with that forecast is represented by the familiar track cone.
The most likely scenario as of 5 p.m. Thursday is for the center of the tropical cyclone to be somewhere in the northwest Caribbean Sea in five days. The more reliable computer models are in fairly good agreement with this, which gives the forecasters pretty good confidence in the track forecast at this time.
There is not as much confidence in the intensity forecast. The current intensity forecast from the National Hurricane Center (NHC) calls for Ernesto to gradually strengthen into a Category 1 hurricane in five days. The best individual intensity model that the NHC had access to last year is currently forecasting a Category 2 hurricane at day five. The Hurricane Weather and Research Forecasting model that NOAA is developing, specifically to improve intensity forecasting, is calling for a Category 1 hurricane in five days. Most other intensity models are calling for various tropical storm intensities.
NHC handles the uncertainty in intensity by issuing probabilities for the maximum sustained winds of the tropical cyclone within various intensity ranges at specific times during the next five days. See the table below for an example.
The NHC forecasters have verified not only their official forecasts but also the computer model forecasts as well for many years. They have been very honest in talking about the need for improved guidance on intensity forecasting. Only time will tell which models will have the best intensity forecasts on Ernesto, but it looks like we are a long way from having any reasonable agreement among the models.