Movement of Tropical Systems

[WeatherWiseGuy]

Newbie question here. After reading some of the threads in here I have noticed that apparently there is some difference in the direction a tropical system may move dependent on whether it develops or not. Is this true? If so, could you please explain? Thanks!

[WindRunner]

I'm not an expert or anything, but I'd tell you that the difference in tracks once it develops is based on a couple of things. One, if a system develops, it is stronger and less likely to be affected by weak outside influences. Two, stronger systems are steered from different layers of the atmosphere, but it all comes down to the fact the models can handle a developed storm better than one that doesn't really exist yet, if it will at all.

[Ola]

Newbie question here. After reading some of the threads in here I have noticed that apparently there is some difference in the direction a tropical system may move dependent on whether it develops or not. Is this true? If so, could you please explain? Thanks!

Weak systems or undeveloped ones move in the direction of the lower levels of the winds sorrounding it.

When a system develops, it gets steered by the direction of winds higher up in the atmosphere, and the stronger a system gets, the higher up you go for wind direction basically. Cyclones move like a swirl in a river, they are steered by the direction of the water on the surface (higher up in the water).

For example, you always see the model output with BAMM and BAMD. The last letter of those mean M= medium and D= deep. Medium is where more weight will be put for direction of wind ie medium height/layer of the atmosphere, where deep is higher up when averaging the winds. If a system were to get really strong, you would look more at the BAMD for direction. Another thing you can deduce from those tracks is that if the BAMM and the BAMD have very different tracks, then there will probablly be shear in the area since that means that winds in different layers are going different directions. But if they are stacked on top of each other, then there is no shear in the area.

Just as a rule of thumb, the stronger a system is, the taller it gets, thus sterred by the higher level winds.