Australians ENSO Update=Chance of el nino between 30-50%

[P.K.]

20th April

Summary - El Niño Chances Remain Elevated.

The chance of an El Niño this year is estimated at between 30 and 50%, which means that the risk is around double what may normally be expected at this time of year. The situation is further complicated by the differences between international computer predictions for the next eight months. The majority of models predict neutral conditions during this period with temperatures somewhat warmer than average, while about one-third of them predict an El Niño. The POAMA model, run at the Bureau of Meteorology, is strongly in favour of an El Niño event developing during the southern autumn and winter. The lack of consensus among the computer models is evidence for why the March to June period is known as the "predictability" barrier: model skill is at its lowest predicting across this span of months.

The latest observations of ocean temperatures, wind, cloud and atmospheric pressure are inconclusive with no clear trends apparent. The "Kelvin wave" of subsurface warming that has been tracked since February, has reached the coast of South America but with little response in surface temperatures in the eastern Pacific as yet. A modest level of cooling has occurred in the western to central tropical Pacific during the past fortnight. However, the Kelvin wave has certainly increased the heat content of the tropical Pacific, and hence provided some "pre-conditioning" of the tropical Pacific for further warming. Another moderate to strong Westerly Wind Burst (WWB) has reached the western Pacific and is expected to produce another Kelvin wave of subsurface warming. Subsurface warming is very important in the development of a basin-wide El Niño, so this latest WWB will be monitored closely, especially as it is occurring in the southern autumn, the critical time of year for El Niño development.

Apart from the WWB, the Trade Winds have been mostly a little stronger than normal during the previous two weeks. Cloudiness around the dateline has been above average so far in April, and the 30-day SOI value has been falling - it currently stands at –3.

Sub-Surface Sea Temps, 900kb



http://www.bom.gov.au/climate/enso/

[cycloneye]

Interesting that they say there observations are inconclusive with no trends one way to another.However during this period between March and June is the most difficult time to predict how ENSO will flip to one side or another.IMO we have to wait for late may or early June to then see how finnally the Kelvin Wave did warm the waters.And also if another Kelvin Wave forms and be as strong as the last one.

[x-y-no]

I know these guys are a lot more expert than I'll ever be - but I have to say I don't see it. Some points to consider:

1) The whole equatorial Pacific is cooler at the surface than it was at this time last year by at least a quarter degree.

2) All of nino-4 is near neutral in the top 100 meters or so, and then cooler than normal for the next hundred meters. It has been cooling slightly for more like a month and a half, not just a fortnight as they say. And that's despite the fact that a fairly strong suppressed convection phase of the MJO passed over the Pacific in March, which ought to have warmed the surface somewhat.

3) The cool anomaly in nino-1/2 is substantially stronger than it was at this time last year, despite the arrival of the Kelvin wave over the last couple of weeks.

4) The latest convective phase of the MJO is weakening, but is still stronger than the one late January to early February which launched the current Kelvin wave, so I agree that we can expect another one to propagate over the next couple of months. But there's less heat to work with in the surface layer of the WPAC, so I'm not convinced ther'll be as much energy in the coming wave as there was in the current one. Since this one had essentially no impact on nino1/2, I really don't see the next one having much impact either.

There is some surface warming in the eastern nino-3 region showing up finally (associated with the surfacing Kelvin wave) but it's hardly impressive as of yet. No doubt the next wave will also have such an effect, at the very least. Nino-3 plays a larger role in the Atlantic shear conditions than nino-1/2 does, so that may impact some of the season. But unless nino-1/2 flips, you're really not going to get a sustained significant warming in nino-3.

Remember, nino-3 and nino-4 were about a degree warm all of last season, and that wasn't enough to suppress cyclone formation in the Atlantic.

[P.K.]

I've been looking to see if the Met Office had anything on this. The following graphs are experimental and are from March:





The first forecast I can find is from this time last year, as below:





As I said at the start of this post remember these are experimental.

[MWatkins]

Well it sure looks like they are backing down. 2 weeks ago they were putting the chances of a Nino at > 50% than normal, now they are down to 30% to 50% greater than normal. This sentence from the full update shows why this (and the previous) El Nino forecast may be on a one-way ticket to bustville:

Preliminary subsurface data for April show that positive anomalies have continued to propagate as a Kelvin wave along the thermocline (the region of greatest temperature change with depth), and have now spread across most of the eastern Pacific. Negative anomalies in the far east have been largely eroded by the Kelvin wave. However, the positive anomalies are not as intense as they were in March (anomalies peak at about +3°C), nor do they have the same large vertical extent, so the potential for a large reponse in surface temperatures has been reduced.

Oh and this one too in reference to the most recent westerly wind burst:

There is some suggestion in the latest data that the WWB is weakening in its eastward penetration, especially along the equator. From the dateline eastwards, the Trade Winds are mainly close to average, i.e. the anomalies are weak.

And this...

Cloudiness near the dateline in the central Pacific is another important indicator of El Niño, as it normally increases during these episodes with a return to near-average values during the decay phase. Cloudiness around the dateline was close to average during March, but has generally been above average during April, although with a decreasing trend over the past week.

So...as we are fond of saying when watching the models flip-flop like [insert favorite political figure here], what does the TREND say.
The Trend is neutral conditions should prevail.

To put it in a hurricane scenario that can be related to...let's just say that El Nino is a tropical storm that looks like it has lost it's low-level circulation in satellite imagery. Recon is on the way to check...and once they get there advisories may be stopped entirely.

I think it will be another 2 weeks before recon gets there.

BOM Austraila full ENSO Update:

http://www.bom.gov.au/climate/enso/#current

MW

[x-y-no]

Yes they do seem to be doing a lot more hedging than they were two weeks ago.

[x-y-no]

Oh and this one too in reference to the most recent westerly wind burst:

There is some suggestion in the latest data that the WWB is weakening in its eastward penetration, especially along the equator. From the dateline eastwards, the Trade Winds are mainly close to average, i.e. the anomalies are weak.

MW

This seems to be supported by the evident weakening of the MJO convective maximum during the last week or so:



Jan