Chances of a La Nina in the Autumn a little reduced

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Paul Garvey

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Jul 18, 2016, 3:57:12 PM7/18/16
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Interesting update from NOAA. Models are suggesting that the chance of a La Nina developing by autumn are a little reduced from last week. Down from a 70% possibility to a 50-60% possibility. 

xmetman

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Jul 18, 2016, 4:18:54 PM7/18/16
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The ONI for May was +0.71°C which is the mean of the SST for April, May & June so we are still technically at the end of a El Nino event. That 3 month mean SST has to fall to -0.5°C or lower and stay there for three successive months for a La Nina to be declared. For that to happen there has to be a continued fall of the SST anomalies, and even if it does its more than likely it won't occur till September at the earliest. My bet is, without diving into the figures, is that NOAA have seen that the latest anomalies are starting to flatline in the mid Pacific.

Paul Garvey

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Jul 19, 2016, 3:32:58 AM7/19/16
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Yes. That's the reason NOAA says 'last El Nino advisory' in yesterday's update. We are technically at the end of an El Nino. A point I'd made to Alastair when he'd said La Nina had started a couple of months ago. ENSO neutral conditions exist across the central Pacific, but you are correct; we are still, technically in an El Nino. La Nina is still months away, by the same technicality and by actual Pacific conditions, if it actually develops! Prediction is notoriously difficult and the model spread on the NOAA site is wide. The model mean would still indicate a La Nina will develop in the autumn and the overall NOAA prediction is that there is still a better than even chance. Those chances do appear to be reducing though. 

It may not be NOAA seeing 'flatlining'. NOAA's own model clearly shows that weak La Nina conditions are likely to develop in the autumn and that they will persist for a few months. It may be the other models' output that NOAA are reacting to. Lots of 'mays' and I may be wrong there and NOAA may be commenting upon only their own model output. Their predictions are, of course, a guesstimate, but I feel the prediction graph of autumn conditions with is possibly based on wider output than their own. Do you have more info on that Bruce, or have I missed something? I'd like to know. 

xmetman

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Jul 19, 2016, 4:30:51 AM7/19/16
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Paul

No I don't have anymore info than you have. I suppose I spent time developing the application that I use to generate the graphics for my blog that I have come to understand the black art that it is!

Beleive it or not the chart of past events that I produce is more accurate than the one from the ESRL site (its all to do with rounding).

http://xmetman.com/wp/enso/

Bruce.

Paul Garvey

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Jul 19, 2016, 10:38:10 AM7/19/16
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Good stuff Bruce! NOAA has values for MAM and AMJ at +1.1C and + 0.7C respectively. MJJ will be below 0.5 and the El Nino will then be officially over. 

Thanks for the info. 


(I can't seen to do slide numbers any more, sorry, but the historical ENSO record is about 2/3 the way through the Power Point.)
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