Slide 10 of 29
For a model to resolve a perturbation, it has to be at least three grid points in amplitude (slightly above the level of “noise”).
Garbage-in; Garbage-out: This term is not intended to downplay the capabilities of Numerical Weather Prediction. It is however intended to emphasize the limitation of data analysis on areas where reliable data is not available for model initialization, as is the case over the open waters of the Tropical Atlantic. In the absence of data, the analysis is only as good as the previous forecast. Thus, if a model forecasts a wave over the Tropical Atlantic, the true nature, or existence, of that wave will not be determined by the numerical model until that perturbation reaches a reliable data source. This is until the wave reaches the Eastern Caribbean where RAOBS and surface observations are routinely available.
Although higher resolution satellite imagery is now available, cloud-drift vector estimates still carry errors large enough to force modelers to give little weight to this information when generating the initial analysis. This is unless the satellite data is also supported by nearby RAOBS and/or pilot reports, which are close to none over the Tropical Atlantic. During the analysis process pilot reports carry more weight than satellite derived data… which underscores the importance of PIREPS.