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    Brett Anderson

    Update on Current La Nina

    9/30/2010, 4:07:21 AM

    I have recently been getting some questions about the current La Nina, so I figured today is as good a day as any to post an update on La Nina.

    Currently, moderate La Nina conditions (cooler-than-normal sea surface temperatures) persist across the equatorial Pacific Ocean at this time. Note the narrow blue area of below-normal sea surface temperatures along the central equatorial Pacific in the image below.


    590x455_09282142_amsr-anom-bb


    Here is a closer-up animation of the sea surface temperature anomalies over the past six months from NOAA.

    Sea surface temperature anomalies have actually risen a bit over the eastern quarter of the equatorial Pacific, but that could be temporary. The remainder of the equatorial Pacific continues to experience little change or even some strengthening of La Nina.

    The latest Oceanic Nino Index (ONI) for August was -1.2, while the combined three-month average ONI reading for June, July and August was -0.6. A reading of -0.5 or less is considered a La Nina.

    Predictions

    The International Research Institute (IRI) for Climate and Society has posted their latest model plume forecast for the ENSO (El Nino Southern Oscillation).


    590x496_09282139_irisst_table


    As you can see, there is a clear consensus among models for a slight strengthening of the La Nina through October, then a leveling off period from November to December. The model consensus predicts a slight weakening of La Nina early next year.

    I looked at the earlier model predictions for this current La Nina, and a clear majority were not strong enough or fast enough in developing the current moderate La Nina.

    According to IRI, Dynamical and statistical model consensus gives a solid 95% chance of La Nina conditions from December 2010 through February 2011. Most models predict at least moderate strength through the winter. Of the models that did not forecast moderate strength, there were a higher number in the strong camp compared to the weak camp.

    -----

    Compare the changes in the global sea-surface temperature anomalies from a year ago.

    Sept. 28, 2009

    590x321_09282148_anomnight


    Sept. 27, 2010

    590x321_09282149_anomnight


    No doubt that La Nina will factor heavily into the winter forecast.

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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