STORM2K

Question:

Are the steeing winds for huricanes at 500 mb? I know that's the level for mid-latitude cyclones, but my met classes haven't really touched on tropical systems.

M

For weaker systems, I tend to use 925-850 mb. For stronger ones, 200-250-300 mb. Mean steering layer though is 500 mb, and models tend to do best at the 500 mb level.

Steering winds will tend to vary with the vertical development of the system.

If you take a look at CIMSS here:

http://cimss.ssec.wisc.edu/tropic/real- ... s-dlm.html

You'll see that there are varying vertical slices of the atmosphere that steer torpical cyclones...notice how the lower the pressure, the lower the steering level int he atmosphere is?

That being said, looking at 500 MB or some other mid-level surrogate (I think WXMAN57 was using 400-7-- MB today) is a great general surrogate for steering winds, especially in situatioans where you are dealing with deep layered ridges and troughs.

Thanks guys! You know, the more i learn about forecasting the more I realize that I have a heck of a lot more to learn!

That's very interesting about the pressure and steering winds. Is that the same with midlatitude cyclone? I.e steering winds decrease in height according to pressure of the central "core"?

M

Mid latitude cyclones are different beasts altogether. they form becasue of horizontal differences in temperature (baroclinic zones) and divergence aloft (usually from troughs aloft and jet streak dyanmics).

Because a mid latitude low is advecting warm and cold air around it, it ends up modifying both the surface baroclinic zone and eventually even the patterns aloft. As it does, it is going to create/enhance pressure falls where the greatest divergence aloft is moving. Where the pressure falls are the greatest, the low will go.

this is a hard concept to get across in a paragraph..but suffice to say that a mid-latitude low is not as "steered" as a tropical cyclone is. Rather, it kind of recreates itself as it moves towards the areas of greatest divergence aloft.

As you can see, Tropical Cyclones are a lot different. Mid Latitude lows control their fate quite a bit more, while mid latitude cyclones are more like corks in a stream (an often used analogy).