The BAMS model

[NickD2011]

Why does the BAMS model always show an extremely unlikely solution? For Irene the BAMS showed it going out to sea every run even when it was close to making landfall in NC. For Katia the BAMS shows it aiming directly for NJ.

[dan88]

The BAM suite of models (BAMS/BAMM/BAMD) each assume a specific depth to the system (shallow, mid, and deep, respectively) for the initial location. As a general rule, the weaker the cyclone, the closer to the surface (more shallow) the flow it follows, as strong cyclones are very deep systems have their movement guided by a much deeper flow then a naked swirl near the surface. The BAMS, no matter how deep the cyclone is in reality, assumes that it will be affected solely by the low level flow, basicly it assumes that the system is not much more than a naked swirl. Because of this, when you have a deep cyclone, the BAMS may give very different results, because the steering flow for a weak and strong system may be quite different. The reverse is true for the BAMD, when you have a depression, or an exposed circulation, the BAMS will likely be much closer to reality than the BAMS, because a developing weak system will be influenced by a much smaller layer of the atmosphere.

This is not to say though that the BAMS on a strong system is useless. While it is true that it does not have much use in determining track, it does help figure out other things, when looking at the BAM suite as a whole. For example, in a low shear environment, there will be relatively small differences in steering regardless of the height, and this can often be seen with all 3 BAM models showing nearly the same track. With a deep, low shear flow, you generally have a nearly uniform wind at all heights. On the other hand, if you have all three ending up in very different places, this is often a signal that there will be significant amounts of shear.

[k***]

They are just old and relatively simplistic models that can't compete with the sophistication of newer ones.