Australians=Chance of el nino 30-50%,Weaker K Wave behind

[cycloneye]

Summary - Eastern Pacific Warms

The chance of an El Niño event occurring this year remains at between 30 and 50%, which means that the risk is around double what may normally be expected at this time of year. Despite a slight easing of the forecast probabilities from the POAMA model, run at the Bureau of Meteorology, it still strongly suggests that an El Niño event may develop during the southern autumn and winter. El Niño impacts upon Australia are generally greatest during winter and spring (see sections below). International computer models vary in their outlooks for the coming months, however the majority favour a neutral, though still warmer than average, tropical Pacific for the remainder of the year. It must be remembered that during March to June model forecast skill is at its lowest.

Current observations continue to show neutral ENSO conditions, however in the past fortnight there has been a warming of the eastern Pacific and the 30-day SOI value has fallen once again, to –11. Whilst cloud over the equatorial Pacific shows no clear signal or trend, the Trade Winds have weakened slightly over much of the region, more so in the west than the east. This may have contributed to a general warming trend of the ocean surface. Furthermore, the "Kelvin wave" of subsurface warming that has been tracked since February, has reached the coast of South America and warmed the far eastern Pacific - the traditional El Niño region. This warming now appears to have spread some distance westward. As a result of changes in the Trade Winds and the warming due to the recent Kelvin wave, the latest weekly data shows a warmer than normal equatorial Pacific from the dateline to the South American coast. This is a significant change since the previous ENSO Wrap Up. If the general weakness in the Trade Winds and the warming of surface temperatures persists for most of May, then the chances of continued development into a basin-wide El Niño will be considerably higher than 50%.

The moderate to strong Westerly Wind Burst (WWB) that reached the western Pacific in mid-April appears to have produced only a weak Kelvin wave of subsurface warming, however as such warming is occurring at a critical time for El Niño development, it will be monitored closely.
Subsurface data for April show that positive anomalies continued to propagate as a Kelvin wave along the thermocline (the region of greatest temperature change with depth), reaching the South American continent during the month. 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 +2.5°C), nor do they have the same large vertical extent, so the potential for a larger response in surface temperatures, due to the Kelvin wave, has been reduced.
Negative anomalies have further intensified and spread from the central to eastern Pacific in the wake of the Kelvin wave, and these may act to further reduce the intensity of the positive anomalies in the east. The image of TOGA TAO subsurface data for the 5 days ending 2nd May shows positive anomalies in the +2 to +4°C range in the far eastern Pacific near the South American coast. It also shows that the top 100 m is warmer than average across the breadth of the tropical Pacific, but weak negative anomalies have developed on the thermocline in central to eastern longitudes. The recent MJO event has produced a weak Kelvin wave in the western Pacific. Though weak, as this is a critical time for El Niño develepment, this will be monitored.



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

However read the last paragrafh and it talks about the next kelvin wave that is weaker than the one that arrived at South America recently.The POAMA model has backed down a little bit from the last update.

In summary what the Aussies are saying with this update at May 4th is good news for those who were a little bit nervous thinking of el nino developing in a more than a weak stage after looking at those bright yellows in the Eastern Pacific at el nino 1-2 and 3.

[Aquawind]

If the general weakness in the Trade Winds and the warming of surface temperatures persists for most of May, then the chances of continued development into a basin-wide El Niño will be considerably higher than 50%.

Considerably higher? hmmmm They are far from throwing the towel in..I doubt the U.S. version of this will give it as much of a chance..If the U.S. suggests a possible El Nino any more than they didn't in the previous forecast I would have to think a real El Nino is a good possibility. I don't really see much of a warming on the West as mentioned though..Seems to me after looking at loops the WPAC surface temps have not warmed much at all and the if anything the warm anomalies have weakened. With the weaker Kelvin expected the chances for significant if any impact from the PAC SSTs seems rather slim..

http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html


Paul

[x-y-no]

Interesting ... I really thought they'd downgrade the probability a little more.

I guess it's a glass half empty/half full thing ... I see nearlyly neutral conditions across most of the basin except where the warming is happening in the east, they see "slightly warm" conditions.

I agree with them about the weakness of the next kelvin wave - one thing they don't mention which I would point out again is that there simply is much less energy available in the WPAC than there was a couple of months ago - and this accounts in large part for the weakness of this wave.

Jan

[cycloneye]

Interesting ... I really thought they'd downgrade the probability a little more.

I guess it's a glass half empty/half full thing ... I see nearlyly neutral conditions across most of the basin except where the warming is happening in the east, they see "slightly warm" conditions.

I agree with them about the weakness of the next kelvin wave - one thing they don't mention which I would point out again is that there simply is much less energy available in the WPAC than there was a couple of months ago - and this accounts in large part for the weakness of this wave.

Jan

In other words it's a 50/50 proposition about seeing el nino but as I said before I lean towards very weak el nino to neutral during the Northern Hemisphere Summer and Fall.