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Archives >> 2005 Storm Forum

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Kevin
Weather Master


Reged: Fri
Posts: 524
Loc: EC Florida
MJO and Whatnot
      #46836 - Sun Aug 07 2005 01:02 PM

It seems as if a lot of people have been wondering about when this hurricane season will truly begin to crank up. I'm going to take a look at a few factors here and try to hazard a guess as to when we'll see the peak of the season start in earnest.

1. The MJO-this is a very important factor as far as moisture and instability in tropical regions goes. The positive phase promotes less moisture for developing tropical systems, the negative phase promotes more moisture (favorable). During the first 3 days of August, we saw the arrival of a negative MJO phase in the Atlantic (green lines). However, this phase was short-lived, and we soon saw another wave of the positive MJO (brown lines) enter the Atlantic Basin. It should be noted that, during that short negative phase, we saw TD9 develop as well as a few other areas of disturbed weather in the Atlantic.

As we look into the longer range (1+ week), there is MUCH larger negative MJO phase that is now working it's way into the EPAC. The difference here is, this phase stretches back towards the WPAC. This means that the next negative MJO phase could have a rather lengthy duration. Although the effects may not be immediate, we should see a general increase in convection across the ITCZ as the negative phase works into the Atlantic.

MJO graphic: http://independentwx.com/MJO30.html

2. Another important factor in favorable ATL conditions is the SOI (Southern Oscillation Index). During most of late July and August, the SOI was negative. This can lead to more El-Nino like conditions (shear) in the Atlantic. However, over the past few days we have seen the SOI steadily head towards positive territory.

SOI data: http://www.longpaddock.qld.gov.au/SeasonalClimateOutlook/SouthernOscillationIndex/30DaySOIValues/

Although the impacts of a positive SOI won't be immediate, we'll likely see a decrease in some of the shear that has been over the basin recently. This, combined with a more favorable phase of the MJO, should allow for a signficant increase in the amount and (perhaps) intensity of upcoming Atlantic cyclones. We could see this increase occur as early as August 15th.

On another note, August 15th is the climo. beginning of the peak hurricane season. It seems as if the factors may be pointing towards a rather normal date as far as increased activity goes.


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HanKFranK
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Reged: Mon
Posts: 1841
Loc: Graniteville, SC 33.56N 81.82W
Re: MJO and Whatnot [Re: Kevin]
      #46847 - Sun Aug 07 2005 01:54 PM

good collection of evidence for the coming pattern, kevin. i wish i knew what the pattern linked to those mini-waves of MJO was, though. i've guessed that it's a delayed response to jitters in the SOI index (or however the two are inter-related. with SOI going positive it looks like the real shift will finally go down in the next week or so.
next question beyond 'when will the storms form' is 'where will they go'. the upcoming pattern GFS keeps advertising is a return to a zonal ridge across the atlantic, with the weakness far to the east, and another over the continent. i'm not sure whether to believe it.
HF 1754z07august


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