Tendenza Stagionale Invernale '16/2017

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Per avere un evento di la nina l'ONI (media trimestrale dell'area nino3.4) deve avere valori minore o uguale a -0.5 per almeno 5 mesi consecutivi...
Per avere condizioni di la nina serve 1 mese minore o uguale a -0.5, un pattern atmosferico da la nina e un forecast per i successivi mesi di condizioni di la nina.
Tutte cose che non ci sono, i forecast più recenti hanno ridotto le possibilità di la nina e favoriscono (nel caso) un episodio debole poichè non c'è stata fino a qui una risposta atmosferica; e in assenza di questa l'anomalia subsuperficiale viene lentamente erosa mantenendo solo deboli anomalie negative, c'è comunque ancora tempo poichè cambino le cose.

July 2016 ENSO discussion: Enjoy neutral while it lasts! | NOAA Climate.gov
Climate Prediction Center: ENSO Diagnostic Discussion

The forecaster consensus is somewhat of a compromise between the two model types, favoring La Niña onset during the August-October season, and predicting a weak event (Niño-3.4 index between -0.5°C and -1.0°C), if an event were to form. Overall, ENSO-neutral conditions currently prevail and La Niña is favored to develop by August - October 2016, with about a 55-60% chance of La Niña during the fall and winter 2016-17

To get a La Niña started, someone—the ocean or the atmosphere—has to make the first move. The ocean has done that—the ocean surface has cooled somewhat, and appears to be “waiting” for some stronger surface winds to upwell still colder water. To get the La Niña to grow, we need more upwelling. It is the atmosphere’s turn to play ball. Is it going to kick in or isn’t it?
Climate forecast models, which look at the latest observations, are beginning to wonder the same thing. Therefore, they recently have become less bullish on the La Niña—both for the rate of onset and the peak strength later in 2016. But they are not forecasting a cancellation of the event, so we need to keep our eyes peeled over the coming weeks and months to see if we get some action.