Bogus GFS Model Forecasts of Atlantic Tropical Cyclone Genesis

[knocker]

 

There are no tropical cyclone threat areas in the Atlantic to discuss today, and none of the reliable models for forecasting tropical cyclone genesis is predicting development over the coming five days. However, the 00Z Friday run of the GFS model predicts that a low pressure area will develop over the Western Caribbean by Wednesday, and push northwards into the Gulf of Mexico and become a tropical storm late in the week. The GFS has been fixated on variations of this idea in all of its runs for the past five days--though the timing of when the predicted storm will form has bounced around from 5 - 11 days into the future. Should we be concerned? A 2013 study by a group of scientists led by Florida State's Daniel Halperin found that we have three models that can make decent forecasts of the genesis of new tropical cyclones in the Atlantic: the GFS, European (ECMWF), and UKMET models. The study only evaluated the model skill for forecasts out to four days in the future, and the forecast skill declined markedly for three- and four-day forecasts. In the current scenario, we are talking about forecasts made much further into the future, which are bound to be low-skill. In addition, the study found that the GFS model had a high incidence of false alarms for tropical cyclone genesis forecasts in the Caribbean (50%). The other two reliable models for predicting tropical cyclone genesis (European and UKMET) had no hint of a low pressure area developing in the Western Caribbean on Wednesday in their 00Z Friday runs. One additional model to consider: the 00Z Friday run of the NAVGEM model is supporting the GFS's idea of a low pressure area forming in the Western Caribbean by Wednesday. The predecessor to this model, the NOGAPS model, was evaluated in the Florida State study, but performed poorly in making tropical cyclone genesis forecasts. However, when two or more models make the same genesis forecast, the odds of the event actually occurring are increased considerably, the study found.

 

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