[Strategerist]

So, now I might ask, isn't it somewhat disconcerting that the storm is undergoing eyewall replacement yet is still a Category 5?

No, it's normal and what you'd expect; A Cat 5 is more likely to replace an eyewall than any other storm, really.

I went through this last night but there's an infinite amount of just flat out wrong stuff about eyewall replacements I see posted here and on weather boards, the source of which I've never been able to determine.

Here's the actual scoop:

1) An eyewall replacement means that a new eyewall develops surrounding the old eyewall (the storm thus looking like a bullseye); when this happens the old eye weakens. Once the old eye is gone, the new outer eyewall is then the storm's main eye, and that eyewall typically contracts in size till it's effectively replaced the original eye. A replacement DOESN'T mean the center of the storm relocates or anything like that.

2) The reason why replacements happen is, well, described in page after page after page of complex fluid dynamics equations in some papers I've found online, none of which I understand. The inner eyewall becomes unstable somehow.

3) Eyewall replacements typically take somewhere in the vicinity of 12 to 18 hours, from the time the new outer eyewall begins forming till the time that eyewall is the sole eyewall of the storm. For various strange reasons people have gotten the weird idea it takes half an hour or a couple of hours, and I've seen assorted clueless types proclaim half a dozen different non-existent "Eyewall Replacements" for one storm in a given day.

4) Eyewall Replacements ALWAYS WEAKEN STORMS. Lot of mythology about that too. While the eyewall replacement takes place, the pressure always rises some and the max wind speed ALWAYS drops. However, the RADIUS of high winds usually gets a lot wider because of the second outer eyewall.

Also, and this is key, a storm doesn't necessarily become stronger after the eyewall replacement than it was before beginning the eyewall replacement. If the storm is more sheared and over cooler water when the replacement is over, it may never restrengthen from the replacement at all. All other things being equal (same shear and water temps) after the replacement is over it will restrengthen to the same strength it was before beginning the eyewall replacement.

[SaveTheChief]

Update from The Woodlands. Due to the fact that I-45 is officially a parking lot, I will not be leaving town. I have been offered shelter at the home of a friend in the area.

It would be a dumb move for me to try and get out of town right now.

I guess for the time being, I will enjoy watching the local news guys talk to the cantankerous old guys who have decided to stay in Galveston.

[.cnI redruM]

>>>>The inner eyewall becomes unstable somehow.


It dissipates into smaller vortexes. Vortexes are how fluids dissipate access KE. They're analogous to frictional heating in solids. The vortex inside the eye wall blows off KE until it can no longer remain intact. At this point, it gets broken into a bunch of smaller vortexes, which in turn get smashed into smaller ones.

[AliVeritas]

Wow, thanks so much... you are a treasure trove of knowledge.

[AntiGuv]

Thank you for the info! You've answered some questions I've been wondering about. It can be confusing at times to separate legit info from the myths. Speaking of which, I recently found out that it's a myth that toilet water spins opposite in the Southern Hemisphere due to the Coriolis effect. That was interesting, and tangentially related to hurricanes. =)