joking, of course.
Ivan Advisories
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Foladar
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clueless newbie
- Tropical Storm
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Re: Ivan-->Florida or Central America
Windfall wrote:matter how you look at it, it seems most probable that either Florida or Central America are going to be nailed with Ivan.
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Note:I am not a professional meterologist. Do not take offense to my ideas. I will admit that my forecast is influenced by 5 years of careful obsrvation of typical storm paths and weather influences. -removed- cannot be ruled out.
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I love that disclaimer
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The winds are starting to gust more noticeably and the electric lines on the poles near my residence are begining to howl just a bit. Also, I saw a couple of very distant flashes of lightning about an hour ago off to my south-east and there are now quite a few low clouds drifting in from the north-east.
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Wainfleeter
- Tropical Depression
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This is my 2nd attempt at posting this, as the electricity went off briefly and I had to restart my computer.
The night was pretty uneventful and judging from what I've been hearing on the radio some people thought that the worst of it had passed.
Well, by daybreak the weather deteriorated significantly and now I'm begining to hear reports of roofs being blown off mainly in the south of the island.
About an half-hour ago, a particularly heavy shower accompanied by strong winds from the east-northeast passed through. I'm not a good judge of wind speeds but I'm pretty sure those were storm force winds!
The night was pretty uneventful and judging from what I've been hearing on the radio some people thought that the worst of it had passed.
Well, by daybreak the weather deteriorated significantly and now I'm begining to hear reports of roofs being blown off mainly in the south of the island.
About an half-hour ago, a particularly heavy shower accompanied by strong winds from the east-northeast passed through. I'm not a good judge of wind speeds but I'm pretty sure those were storm force winds!
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AdvAutoBob
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donsutherland1
- S2K Analyst
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Ivan: Possible Sub-920 mb Hurricane?
Based on an examination of six past sub-920 mb hurricanes for which a large amount of pressure data is available, the odds of Ivan's growing into a sub-920 mb hurricane are low but not zero.
The hurricanes assessed were:
Allen (1980): 899 mb
Gilbert (1988): 888 mb
Hugo (1989): 918 mb
Isabel (2003): 915 mb
Mitch (1998): 906 mb
Opal (1995): 916 mb
All of these hurricanes met the following criteria:
• Had an explosive deepening phase (drop of 26 mb or more over a period of 24 hours or less)
• Saw no increase of more than 5 mb in pressure prior to first dropping below 920 mb after or during the explosive deepening phase
A look at "near-misses" or hurricanes that achieved 920 mb to 925 mb minimum pressures also reveals that such storms typically meet the above criteria for sub-920 mb storms. Only one such "near-miss" hurricane had experienced a pressure increase that exceeded the above criteria.
Those storms examined were:
Andrew (1992): 922 mb
David (1979): 924 mb
Floyd (1999): 921 mb
Gloria (1985): 920 mb
David saw a brief 6 mb rise but only after interaction with the Antilles before resuming its drop to 924 mb.
Thus, if one looks for a sub-925 mb storm, one likely needs to look for the following:
• An explosive deepening phase (drop of 26 mb or more over a period of 24 hours or less)
• No increase of 10 or more mb in pressure prior to first dropping to or below 925 mb after or during the explosive deepening phase
Ivan saw its central pressure increase 21 mb after its explosive deepening phase brought it to 948 mb (a drop of 39 mb in 15 hours). At the same time, this increase in pressure occurred without any interaction with land.
With its initial explosive intensification phase having failed to see a sustained drop in the pressure, against the above criteria, it would appear that Ivan would not become a sub-920 mb hurricane.
However, there may be some data that suggests that Ivan's prospects for strengthening below 920 mb might not been eliminated altogether:
Hurricane Allen saw its central pressure rocket 32 mb and then come back down explosively, but after Allen had initially achieved sub-920 mb status. What happened is that Allen saw two significant pressure increases due to interaction with land:
<img src="http://weather.unisys.com/hurricane/atlantic/1980/ALLEN/track.gif">
Nevertheless, working against this idea, one could make the argument that Allen was in a sustained explosive deepening phase and it was only the interaction with the land and not the termination of the explosive deepening that led to its increases in pressure.
Another argument for possible strengthening beyond 920 mb would be the small sample size. Unfortunately, large amounts of pressure data are not available for addition sub-920 mb hurricanes such as Camille.
Based on the above information, I believe that the odds of Ivan's growing into a sub-920 mb hurricane are low but not necessarily zero.
A quick but important note: This is based on historical data. One will also need to consider the synoptic setup and Gulf of Mexico environment (SSTAs, depth of very warm the 26°C water, etc.).
It will be interesting to see how things ultimately work out.
The hurricanes assessed were:
Allen (1980): 899 mb
Gilbert (1988): 888 mb
Hugo (1989): 918 mb
Isabel (2003): 915 mb
Mitch (1998): 906 mb
Opal (1995): 916 mb
All of these hurricanes met the following criteria:
• Had an explosive deepening phase (drop of 26 mb or more over a period of 24 hours or less)
• Saw no increase of more than 5 mb in pressure prior to first dropping below 920 mb after or during the explosive deepening phase
A look at "near-misses" or hurricanes that achieved 920 mb to 925 mb minimum pressures also reveals that such storms typically meet the above criteria for sub-920 mb storms. Only one such "near-miss" hurricane had experienced a pressure increase that exceeded the above criteria.
Those storms examined were:
Andrew (1992): 922 mb
David (1979): 924 mb
Floyd (1999): 921 mb
Gloria (1985): 920 mb
David saw a brief 6 mb rise but only after interaction with the Antilles before resuming its drop to 924 mb.
Thus, if one looks for a sub-925 mb storm, one likely needs to look for the following:
• An explosive deepening phase (drop of 26 mb or more over a period of 24 hours or less)
• No increase of 10 or more mb in pressure prior to first dropping to or below 925 mb after or during the explosive deepening phase
Ivan saw its central pressure increase 21 mb after its explosive deepening phase brought it to 948 mb (a drop of 39 mb in 15 hours). At the same time, this increase in pressure occurred without any interaction with land.
With its initial explosive intensification phase having failed to see a sustained drop in the pressure, against the above criteria, it would appear that Ivan would not become a sub-920 mb hurricane.
However, there may be some data that suggests that Ivan's prospects for strengthening below 920 mb might not been eliminated altogether:
Hurricane Allen saw its central pressure rocket 32 mb and then come back down explosively, but after Allen had initially achieved sub-920 mb status. What happened is that Allen saw two significant pressure increases due to interaction with land:
<img src="http://weather.unisys.com/hurricane/atlantic/1980/ALLEN/track.gif">
Nevertheless, working against this idea, one could make the argument that Allen was in a sustained explosive deepening phase and it was only the interaction with the land and not the termination of the explosive deepening that led to its increases in pressure.
Another argument for possible strengthening beyond 920 mb would be the small sample size. Unfortunately, large amounts of pressure data are not available for addition sub-920 mb hurricanes such as Camille.
Based on the above information, I believe that the odds of Ivan's growing into a sub-920 mb hurricane are low but not necessarily zero.
A quick but important note: This is based on historical data. One will also need to consider the synoptic setup and Gulf of Mexico environment (SSTAs, depth of very warm the 26°C water, etc.).
It will be interesting to see how things ultimately work out.
Last edited by donsutherland1 on Tue Sep 07, 2004 2:52 pm, edited 2 times in total.
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Hurrilurker
- Category 2
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Just curious, when Ivan "rapidly deepened", was the initial pressure an estimate or confirmed by recon? Because I seem to remember the NHC consistently erring on the conservative side (underestimating) the official strength for quite a while, although they always mentioned the potential for rapid strengthening.
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donsutherland1
- S2K Analyst
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- Location: New York
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donsutherland1
- S2K Analyst
- Posts: 2718
- Joined: Mon Sep 15, 2003 8:49 pm
- Location: New York
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donsutherland1
- S2K Analyst
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- Joined: Mon Sep 15, 2003 8:49 pm
- Location: New York
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