| CoconutCandy |
| (User) |
| Sun Aug 03 2008 08:11 AM |
|
Can a Thunderstorm Outflow Boundary 'Tame' the Mighty Hurricane?
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What's that you say? Preposterous! Absurd! Say it ain’t so!
Well, guess what? This actually may be the case under very special circumstances. Read on ...
While we're all keeping an eye on a number of 'invests', (TCFA now issued for Invest 91L in the GOM) and before the next round of storms crank up, I thought I'd take this opportunity to share with you a very interesting hurricane story.
( This is actually a reply to "WHAZZAT?", posted earlier this season in this forum.
http://flhurricane.com/cyclone/showflat.php?Cat=0&Number=80152&an=0&page=0#80152 )
That post reminded me of an interesting article I came across a few years ago while web surfing.
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Who remembers the hurricane season of 1995? Yep. It was a pretty active year. If fact, it was thee *most* active hurricane season of the 20th century, second only to 1933 !! It brought us the likes of landfalling hurricanes Erin and Opal (who can forget Opal?) and a number of other historically interesting storms, including Luis, Marilyn and Roxanne.
( For those interested: http://en.wikipedia.org/wiki/1995_Atlantic_Hurricane_season )
It was Major Hurricane Luis that was 'tamed' by the aforementioned thunderstorm outflow boundary. OK. OK. I guess it depends on what you mean by 'tamed'.
The following excerpts are from a very cool 4-page article appearing in the prestigious journal "Monthly Weather Review". In fact, it was featured as the "Picture of the Month", for the September 2000 issue.
For those interested in reading and studying the original article (in PDF format):
http://rammb.cira.colostate.edu/resources/docs/Hurr_Luis.pdf
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Luis was a Cat 4 storm at the time, that had just crossed the northernmost of the Lesser Antilles. To make the story short (read the article for the whole scoop), a very large, low-level thunderstorm outflow boundary (LTO) formed and propagated outward in the NW quadrant of Luis.
Quote:
" ... a large LTO boundary emerged from beneath the cirrus cloudiness on the northwest side of the storm. (See the following graphic) ... Since the storm was traveling toward the northwest at this time, the LTO boundary, and the region of stable air associated with it, were being positioned just ahead of the storm’s center. When the hurricane’s core crossed into the area where this outflow air had spread, the stable air appeared to have had a strongly negative influence on the eyewall convection."
Quote:
" ... Although there was no significant weakening of maximum winds, or increase of mean sea level pressure, this disruption of the eyewall structure did appear to interrupt the intensification trend the storm was experiencing. ... It is also interesting that after the storm passed beyond the area of more stabilized boundary layer air, it once again began to become better organized and resumed its intensification."
In Summary ...
Quote:
"1) A period of moderately intense wind shear and dry air intrusion caused the eyewall convection to ingest dry midlevel air and weaken
2) The collapsing convection produced a very stable LTO air mass ahead of itself
3) The convection near the center of the hurricane passed over this stable, low-level air mass and weakened
4) Once out of this region, the storm reintensified.
So, the LTO boundary 'tamed', or at least 'held in check', an intensification phase that Luis was going through.
This shortened, condensed version doesn't really do the article justice, and I heartedly encourage all you hard-core hurricane buffs to read the PDF, which has additional illustrations and a more thorough explanation of the actual dynamics involved.
Pretty interesting stuff in my book. Hope you will enjoy the article as much as I did!