Sometimes people ask why the National Hurricane Center only discusses tropical cyclone development out to two days when computer models are run for much longer time periods. Let’s look at a couple of examples.
One of the consistently best computer models for forecasting tropical cyclone tracks is from the European Center for Medium Range Weather Forecasts (ECMWF). We will take a look at what this specific model has done with the strong tropical wave currently over the eastern Caribbean Sea.
The above figure is a ten day forecast from the ECMWF model run initialized at 00Z on June 21st (8 pm EDT June 20th). This particular model run showed significant development of the tropical wave. Note the very strong low pressure system near the Mississippi/Alabama coast.
This figure is a ten day forecast from the same ECMWF model but initialized 12 hours later at 12Z on June 21st (8 am EDT June 21st). Note the very weak low pressure system over the western Gulf of Mexico near the Texas/Mexico border that also developed from the tropical wave currently over the eastern Caribbean.
This is a tremendous difference in the ten day forecasts from these two back-to-back model runs. There is no denying that computer models are much improved in recent years, but these two examples clearly show there is a lot of room for improvement at the longer time periods.