[Dave K]

According to http://iri.columbia.edu/climate/ENSO/currentinfo/technical.html, comes from a part of Columbia University I think

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As of mid-September 2011, SST anomalies have moved into weak La Niña territory in the central and eastern equatorial Pacific. For August the SST anomaly in the NINO3.4 region was -0.64 C, indicative of weak La Niña conditions, and for the June-August season the anomaly was -0.36 C.

Presently,the models and observations taken together indicate probabilities of approximately 52% for maintaining at least weak La Niña conditions, 48% for returning to ENSO-neutral conditions, and near 0% for developing El Niño conditions, during the Sep-Nov 2011 season in progress. Probabilities for La Niña rise to 53% for the Oct-Dec 2011 season. Probabilities for El Niño conditions remain below 10% through Feb-Apr 2012. La Niña conditions are the most likely scenario during the remainder of 2011 and into very early 2012, but by a fairly small margin over neutral conditions.

[Dave K]

A slight update from the 6th October

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Currently, La Niña is not as strong as it was in September 2010. Roughly one- half of the models predict La Niña to strengthen during the Northern Hemisphere fall and winter (Fig. 6). Of these models, the majority predict a weak La Niña (3-month average in the Nino-3.4 region less than -0.9°C). In addition, a weaker second La Niña winter has occurred in three of the five multi-year La Niñas in the historical SST record since 1950. However, the NCEP Climate Forecast System (CFS.v1) predicts a moderate-strength La Niña this winter (between –1.0°C to –1.4°C) and CFS.v2 predicts a strong La Niña (less than –1.5°C), which rivals last year’s peak strength. For CFS forecasts made at this time of year, the average error for December-February is roughly ±0.5°C, so there is uncertainty as to whether this amplitude will be achieved. Thus, at this time, a weak or moderate strength La Niña is most likely during the Northern Hemisphere winter.

http://www.cpc.ncep....ry/ensodisc.pdf

[Dave K]

Latest update suggests that a weak to moderate La Niña over the NH winter is still the most likely projection.

http://iri.columbia.edu/climate/ENSO/currentinfo/QuickLook.html

[Dave K]

Latest info is from the 10th November at http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

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A majority of the models now predict La Niña to continue through the Northern Hemisphere winter (Fig. 6) and then gradually weaken after peaking during the November - January period. The models are roughly split between those that predict La Niña to remain weak (3-month average in the Niño-3.4 region less than -0.9oC) and those that predict a stronger episode.

During November 2011-January 2012, there is an increased chance of above-average temperatures across the south-central U.S. with the odds favoring below-average temperatures over the north-central U.S. Also, above-average precipitation is favored across the northern tier of states, excluding New England, and drier-than-average conditions are more probable across the southern tier of the U.S.

The Australia BOM ( http://www.bom.gov.au/climate/enso/ )says:

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Forecast models surveyed by the Bureau suggest the event is likely to peak towards the end of 2011, and persist into early 2012. It is considered unlikely that the current La Niña will be as strong as the La Niña event of 2010-11.

The northern Australian outlook for November 2011 to January 2012 shows the following:
- a wetter season is more likely over northern Australia
- a warm Indian Ocean is the main contributor to this wet outlook
- a wetter season is likely for most of southeastern Australia
- strongest probabilities occur in northeastern NSW
- no strong signal for Victoria or Tasmania
- A persistently warm Indian Ocean is the main driver behind this outlook, although it is also consistent with the devloping La Niña in the Pacific Ocean.

[Dave K]

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La Niña continues over the Pacific Basin
Issued on Wednesday 21 December | Product Code IDCKGEWWOO

La Niña remains in place across the tropical Pacific, though the majority of climate models surveyed by the Bureau suggest the La Niña may be near its peak. While the event is likely to persist through the remainder of summer, a gradual decline in the strength of the La Niña is expected over the coming months.

Climate indicators of ENSO continue to exceed La Niña thresholds, but remain weaker than at the same time in 2010. Despite some local warming over the past fortnight, tropical Pacific Ocean temperatures remain cooler than normal. Atmospheric indicators of La Niña strengthened over the last fortnight – for example, the current 30-day SOI value of +21 is the highest since the breakdown of the 2010-11 event in May 2011. Australia’s climate has responded to these changes in the tropical Pacific, with above average rainfall across large parts of the country since October.

La Niña periods are usually, but not always, associated with above normal rainfall during the second half of the year and summer across large parts of Australia, particularly the eastern and northern regions. Daytime temperatures are typically cooler than average and tropical cyclone risk for northern Australia increases during the cyclone season (November to April), with February and March the peak. For detailed rainfall and temperature outlooks, please see: www.bom.gov.au/climate/ahead.

[Dave K]

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A borderline weak/moderate La Niña event continues in the equatorial Pacific, where sea surface temperatures were approximately 1.0°C below average during January and the the first half of February.

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Most of the set of dynamical and statistical model predictions issued during late January and early February 2012 predict La Nina conditions for the February to April 2012 season currently in progress, transitioning back to neutral conditions during the March-May season.

http://iri.columbia..../SST_table.html

[Dave K]

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La Niña drawing to a close

La Niña, the cooling of the equatorial Pacific waters off the coast of South America that has dramatically affected our weather for most of the past two years, is almost done. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", have warmed rapidly over the past two weeks, and were 0.4°C below average on February 27. This is slightly warmer than the -0.5°C threshold to be considered La Niña conditions, and is the first time since early August that La Niña conditions have not been present. It is likely that SSTs will continue to warm during March and April, and NOAA's Climate Prediction Center is predicting that they will declare an official end to La Niña sometime between March and April.

http://www.wundergro...l?entrynum=2040

[John Mason]

I see a 32% chance of El Nino conditions by late summer is the current thinking - that'll calm down the hurricane-season should it come off.

Cheers - John

[ldavidcooke]

Hey All,

Mos indications are this summer here in the NH, are we are in a transition phase or neutral conditions. These are usually marked by stagnant high pressure over the Atlantic coast, wth most of the tropical-subtropical moisture moving up the Western side of the Appies. Generally this portends that most of the sub-tropical storm activity will.be in the GoM early in the season and well off shore late in the season. If this pattern hold to the last decade, the El Nino phase will begin to fade by Nov. and lead into heavy snow and winter weather late next Fall.

If the El Nino does not re-establish itself, the La Nina pattern will likely return, making this one of the longest lasting La Nina patterns in modern memory... This is a wnderful time to observe the MDO and NAO interactions. This is likely one of the best times to try to figure the large pattern drivers and feedbacks. I suspect with this being the third year of a similar pattern being observed that a new theory wrt atmospheric heat flow may emerge by early next Spring..., can't wait.

[Bazmundo]

Wasn't the 2011 US Tornado Season a weakening La Nina as well? That's possibly not good news for the Mid-West.

[Martyn Wells]

ldavidcooke, on 29 February 2012 - 12:57, said:

[snip]. Generally this portends that most of the sub-tropical storm activity will.be in the GoM early in the season and well off shore late in the season. [snip]

Early season activity is normally based almost exclusively on GoM regardless of ENSO conditions, as GoM is the only part of the basin with sufficient SSTs to support development and subject to the location of the sub-tropical jet. Early season ITCZ still is burried deep into South America, and the wave train barely capable of producing any decent strength waves.

[ldavidcooke]

Martyn Wells, on 29 February 2012 - 13:57, said:

Early season activity is normally based almost exclusively on GoM regardless of ENSO conditions, as GoM is the only part of the basin with sufficient SSTs to support development and subject to the location of the sub-tropical jet. Early season ITCZ still is burried deep into South America, and the wave train barely capable of producing any decent strength waves.

Hey Martyn,

Full agreement here. The most notible condition with a transition phase from a La Nina to an El Nino is a southerly domain of the sub-tropical winds resulting in less shear above 25 deg. N. The result appears to be the Caribbean convection rapidly moves northward in the early TS season.