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General Discussion >> Hurricane Ask/Tell

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Allison
Weather Guru

Reged:
Posts: 134
Loc: Laredo, Texas

Dean and the ULL

#76765 - Fri Aug 17 2007 08:11 PM

My question relates to the potential interaction between Dean and the upper level low over the Bahamas.

Just about everything I know about hurricanes, I've learned from this board

, and I've read the posts on this issue, including Clark's blog entry earlier today.

Here's where I'm still confused:

Ridges push storms west; lows/troughs pull storms north -- I got that much, at least.

So if the ULL moves into the GOM ahead of Dean, why does the forecast pull Dean only moderately to the right and into TX/LA. In other words, why doesn't the low recurve Dean into Florida or the eastern GOM?

I suspect it has something to do with the intensity of the low v. the intensity of Dean, but if anyone can explain this in more detail, I'd appreciate it.

Second question -- if the ULL ends up having little or no affect on Dean, what will then be the primary steering mechanism?

Thanks!

--------------------
Allison

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Myles
Weather Hobbyist

Reged:
Posts: 80
Loc: SW FL

Re: Dean and the ULL

[Re: Allison]
#76770 - Fri Aug 17 2007 08:47 PM

The reason the ULL is forecast to have less of an effect is because it is cutoff from the jet stream and lacks any real extending fronts/trofs. Because of that the ULL isn't creating a path to the westerlies that the hurricane can follow. So instead of recurving it, it will only nudge it north. Also, because most of the energy is in the upper levels, the ULL can cause shear since the upper level winds are strong cyclonically, but the surface winds are mostly easterly. And the intensity of the low is also important. A weak ULL is less likely to have a surface/mid-level reflection(low pressure at the surface/mid-layer as well as the upper levels) and less of an impact on storm motion.

However, an important factor is that ULL's don't really recurve storms. Storms recurve due to fronts/troughs associated with extra-tropical storms. The main difference is that extra-tropical storms usually have low pressure centers from the upper levels to the surface and are embedded in the jet stream. Cutoff lows like the one in the Bahamas don't influence tracks as much as they can create shear.

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