HanKFranK
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there's a list of large scale atmospheric indicators i could think of that have effects on tropical cyclone activity/general circulation in the atlantic during the season.. on a scale that can be measured in a few days to a few weeks. i was thinking a forum post here to get people to discuss how they work and where information on them can be acquired, addition of links, and observations of how they affect current weather might be appreciated by some of ya. so if anybody has a comment, question, link, etc.. go ahead and add it.
HF 0433z09september
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HanKFranK
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thought i'd toss this one up first since i'm watching it against our current weather in the u.s. and the status of the atlantic ridge. i got this info from steve in metairie, la... and he from watching joe bastardi.
SOI is a southern oscillation index.. it's related to pressure anomalies in the south pacific. i'm not really certain of the details, but what i could glean from steve's info is how changes in the index correspond to changes in the global circulation. the timing and amplitude of troughs seems closely linked to changes in index. here's the 30-day index from a site called 'the long paddock' from australia.
Date Tahiti Darwin Daily** 30 day 90 day
Av.SOI Av.SOI
----------------------------------------------------------------
11-Aug-2003 1015.34 1011.95 10.70 -0.37 -6.25
12-Aug-2003 1015.19 1012.80 4.60 -0.18 -6.24
13-Aug-2003 1015.44 1013.30 3.10 0.13 -6.26
14-Aug-2003 1014.41 1012.45 2.00 0.76 -6.20
15-Aug-2003 1013.34 1011.15 3.40 1.33 -6.22
16-Aug-2003 1013.19 1011.80 -1.40 1.27 -6.33
17-Aug-2003 1013.78 1012.95 -4.80 0.85 -6.32
18-Aug-2003 1013.34 1012.95 -7.40 0.24 -6.19
19-Aug-2003 1013.41 1012.00 -1.20 -0.33 -6.05
20-Aug-2003 1014.91 1010.90 14.50 -0.37 -5.69
21-Aug-2003 1014.98 1011.60 10.60 -0.27 -5.43
22-Aug-2003 1016.10 1012.15 14.10 0.41 -5.12
23-Aug-2003 1015.69 1011.95 12.80 0.82 -4.80
24-Aug-2003 1014.24 1011.45 7.00 0.83 -4.33
25-Aug-2003 1012.45 1012.40 -9.50 0.28 -3.93
26-Aug-2003 1014.19 1013.55 -5.90 0.05 -3.64
27-Aug-2003 1014.33 1013.95 -7.50 0.01 -3.54
28-Aug-2003 1014.91 1015.25 -11.80 -0.23 -3.54
29-Aug-2003 1013.76 1014.10 -11.80 -0.61 -3.50
30-Aug-2003 1013.83 1013.95 -10.50 -0.98 -3.40
31-Aug-2003 1014.00 1013.40 -6.10 -0.69 -3.31
1-Sep-2003 1014.25 1013.35 -8.40 -0.27 -3.41
2-Sep-2003 1014.30 1014.15 -12.90 -0.22 -3.56
3-Sep-2003 1013.59 1014.85 -21.20 -0.58 -3.61
4-Sep-2003 1014.36 1015.50 -20.50 -1.24 -3.65
5-Sep-2003 1015.15 1014.45 -9.60 -1.71 -3.59
6-Sep-2003 1015.41 1013.60 -3.00 -1.80 -3.50
7-Sep-2003 1014.54 1013.40 -7.00 -1.91 -3.39
8-Sep-2003 1015.39 1013.50 -2.50 -2.25 -3.23
9-Sep-2003 1016.20 1012.75 6.70 -2.47 -2.90
the middle number, 6.70, is the daily value. note that it is the first positive value since august 24th.
now, the limited ability i have to interpret it is from what steve told me.. the value correlates to the amount of amplitude of troughing in the eastern united states roughly 15 days later. negative values tend to correspond to a flat, zonal pattern (like in NAO positive), while positive ones correspond to troughing in the east, common to NAO negative.
now, here's what we've had. the troughing that took fabian out corresponded to the positive values from august 20th to 24th (fabian recurved around september 3-6, roughly two weeks later). today there is generally flat ridging across the atlantic.. and we correspond to the negative value of august 26th. note that was negative from august 25th to september 8th.. with a strong signal for much of the period, with a slightly weaker signal in the middle and a slow taper at the end. that weak middle signal was around aug31-sep1.. corresponding to sep 14-15.. the time the shortwave is forecast to weaken the ridge temporarily. since was strongly negative in the following days, i'd suspect the ridge will be flat and established next week.. and quite possibly take isabel all the way westward.
this is a crude method, but these signals do correspond to real weather events.. we can watch how isabel progresses over the next few days and see how much merit it has in this case.
HF 2247z09september
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MikeC
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I was looking for something to make me think less Fish Spinner, you found it. Good one Hank. I'll be keeping an eye on this as well.
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javlin
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Frank may I ask a few questions.(1)What effect will the ULL have on the ridge to the N is it buffering it more N.Then allowing or raising the ceiling allowing more head room for Isabel.(2)They both appear to be moving about the same speed.Is the ULL possibly clearing a pathway.A vacuum path of least resistence.(3)If Isabel did gain speed on the ULL could it be sling shoted over the ULL.I realize some serious compression of Isabel would take place.I just never forgot how Claudette did that ULL .The well taken and understood very plausible explanation.
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HanKFranK
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those are questions for a real met.. but i'll try to answer them.
i can't describe the ridge to the north and it's relation to the other features other than to say it's THERE. its strength and configuration is more related to the longwave pattern.. right now we're transitioning back to NAO positive.. a flatter pattern.. and the ridge is sort of unbunching and pancaking across the atlantic. the upper features are responding to this by becoming progressive underneath.. you did note the tandem movement of the upper lows and isabel. their presence requires there to be an upper high between, in this case isabel's outflow. all of these systems are at outflow level.. 200-300mb... the ridge is more of a 500mb feature. bastardi if i remember uses the 400mb contour for the hurricane's path. anyhow, about the slingshot thing.. the systems are all moving together.. but they can apply the squeeze to one another. isabel is strong though.. and can push back. eyewall contraction cycles and fabians wake might weaken it quite a bit (remember georges going from borderline cat5 to high cat2 as it approached the virgin islands?).. but very unlikely to kill it outright.. even if it does weaken it will stay further south and go with a shallower flow. i probably killed the answer i was trying to give in all of that explanation.. but hopefully you can sort it out of my attempts to explain something i'm utterly fascinated by but am not an official source of understanding on.
take it easy.
HF 0358z10september
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javlin
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I read that that post from Gray and it answer some of the questions.These were just thoughts I had scenarios that could play.I believe it plays further W than anticpated,how far I can not say yet.I will continue to watch the ridge and the ULL.These well provide our info for the next few days.
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clyde w.
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Javlin--
Gray posts daily at that link. I read him any time a storm is threatening. He gives great detail.
PS- I also read HankFrank every time he posts. He cuts through the wishing and hoping and spells it out pretty nicely. He is much appreciated on the board.
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Steve
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Yeah HF,
That's pretty much the way I understand the . Because it's primarily an Austrailian index, not that many people follow it. But it is a pretty uncanny value for 15-day downstream US implications. Tonight is the 3rd night positive suggesting amplification 23rd-25th.
Steve
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MF'n Super Bowl Champions
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HanKFranK
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it's proving handy so far, steve. when i can find a useful explanation for besides 'upper atmosphere wave propagating eastward from the indian ocean' i'll post some info and stats on it. as far as NAO, AO, PNA.. those are more often used for wintertime weather.. but i'll try and work them in somehow if i can find info sources.
HF 1407z11september
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HanKFranK
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i'll post some kind of data later. too much to do right now.
HF 1751z12september
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HanKFranK
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MJO. the madden julian oscillation.
there are a couple of things i understand about it, if only in a layman sense.
mjo is an inhibiting/enhancing factor in convective activity in the tropics.. its positive phase causes anomolously poor conditions at outflow levels for intense convection, while its negative phase is often timed with bursts of tropical cyclone activity in whatever basin it happens upon.
the wave is a high altitude feature, it occurs at outflow levels.. and i'm not certain, but do believe its relative strength and effect on global weather patterns is related to the monsoon down there.. which is itself linked to various other factors. it comes more in an amorphous patch than a wave, as it propagates eastward around the globe.. pulsing and deforming its coverage area... but i'd imagine if plotted on an graph it's would appear as a waveform.
this doesn't seem to be the year to get in to how much of an effect has had.. because it has been pronounced at times (fabian, grace,henri, isabel, and TD14 came about during a recent passage, after a erika and a mere depression over the previous month).. but not as much as in certain recent years. if another arrives at what seems to be the regular interval for the season.. we should get another burst of activity in mid-october. right now conditions appear neutral to negative for most of the basin.. the rest of september will probably be fairly quiet, aside from that large hurricane currently out still out there.
HF 1525z13september
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SandiaFlower
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There just seems to be so many factors that play into this. Many that we are not aware of yet their effects. Hank,MikeC and JaxJoe why is it that is ignoring the possibility of a Florida hit? Scares me that many people are just looking at that one projection and thinking this will all pass safely.........truly this will be the longest weekend in my whole life.
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HanKFranK
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i'll have to go dig up some more info for these. schoolwork is heavy at the moment and it may be a few days before i can post any data. of course, if somebody ELSE would go do the research..
anyhow, looks like the didn't verify as well as i'd have hoped. our storm was still carried far to the west, and it still wants to go to the west.. but if was correlating correctly the ridge would be surging again.. it is, but not zonally... more amplified than a high positive would indicate.
HF 1817z16september
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