I have a question...

[Anonymous]

I like using the "mb voricity" models at this page.
http://met.psu.edu/tropical/tcgengifs/
Which mb (850,350, ect) would indicate a surface spin? Not something at the upper levels.

[Derecho]

For following waves, storm formation or TDs, yep, the vorticity plots are MUCH better than surface pressure.

None of the vorticity plots on any of the models are actually AT the surface.

Just select the one with the "highest" mb, (950mb, 850 mb) and you'll see a representation of vorticity JUST ABOVE the surface.....this is where many tropical waves have most of their spin, even when there is nothing at the surface.

200 mb is the top of the troposphere.

[Rainband]

Thanks Derecho

[MWatkins]

I like using the "mb voricity" models at this page.
http://met.psu.edu/tropical/tcgengifs/
Which mb (850,350, ect) would indicate a surface spin? Not something at the upper levels.

Derecho covered this pretty well so i'll only add some detail.

I always use the 950MB plots to determine the location of tropical systems in the models (or close to that...NOGAPS resolves down to 850, UKMET and the CMC get to 925MB). You have to be careful with that because the GFS/AVN spins up suspicious looking vort maxes in th ITCZ all the time...especially after 96 hours. But if you use that plot along with the surface pressure contours...you're in good shape.

Remember that 950MB is still at least 500 meters above the surface (in the standard ocean pressure backgound it's closer to 512 meters)...you may have a closed low at 950 and still not have one at the surface. I think my math is right there...

To pinpoint mid and upper lows...take a look at the plots starting at 300MB and work downward to see how deep a system is.

Here's the GFS run in t+24 hours. Note the upper low located in the Bahamas at 300MB:

http://bricker.met.psu.edu/trop-cgi/avn ... hour=024hr

Note that by the time you get down to the mid-layer (500mb) it doesn't even reflect in the vorticity fields:

http://bricker.met.psu.edu/trop-cgi/avn ... hour=024hr

And by the time you overlay the surface pressure map (and you an also look at 950MB vort fields too) this is a shallow upper low that has relatively high surface pressure...no threat to work down to the surface:

http://bricker.met.psu.edu/trop-cgi/avn ... hour=024hr

Check out that huge middle lattitude system in eastern Canada. Now that's a deep layer system (although of course not tropical).

Hope this helps...

MW