It’s official: La Niña has developed in tropical Pacific

La Niña Advisory is issued when La Niña conditions are observed and expected to continue.

EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION issued by CLIMATE PREDICTION CENTER/NCEP/NWS and the International Research Institute for Climate and Society

9 November 2017

ENSO Alert System Status: La Niña Advisory

Synopsis: La Niña conditions are predicted to continue (~65-75% chance) at least through the
Northern Hemisphere winter 2017-18.

During October, weak La Niña conditions emerged as reflected by below-average sea surface
temperatures (SSTs) across most of the central and eastern equatorial Pacific Ocean (Fig. 1). The weekly
Niño indices were variable during the month, with values near -0.5 C during the past week in the Niño-
3.4 and Niño-3 regions (Fig. 2). Sub-surface temperatures remained below average during October (Fig.
3), reflecting the anomalously shallow depth of the thermocline across the central and eastern Pacific
(Fig. 4). Also, convection was suppressed near the International Date Line and slightly enhanced over
parts of the Maritime Continent and the Philippines (Fig. 5). Over the equatorial Pacific Ocean, low-level
trade winds were mainly near average, but the upper-level winds were strongly anomalously westerly and
the Southern Oscillation Index was positive. Overall, the ocean and atmosphere system reflects the onset
of La Niña conditions.

For the remainder of the Northern Hemisphere fall and winter 2017-18, a weak La Niña is
favored in the model averages of the IRI/CPC plume (Fig. 6) and also in the North American MultiModel
Ensemble (NMME) (Fig. 7). The consensus of forecasters is for the event to continue through
approximately February-April 2018. In summary, La Niña conditions are predicted to continue (~65-75%
chance) at least through the Northern Hemisphere winter (click CPC/IRI consensus forecast for the
chance of each outcome for each 3-month period).

La Niña is likely to affect temperature and precipitation across the United States during the
upcoming months (the 3-month seasonal temperature and precipitation outlooks will be updated on
Thursday November 16th). The outlooks generally favor above-average temperatures and below-median
precipitation across the southern tier of the United States, and below-average temperatures and abovemedian
precipitation across the northern tier of the United States.

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration
(NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric
conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current
Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum of CPC’s
Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog.
The next ENSO Diagnostics Discussion is scheduled for 14 December 2017. To receive an e-mail
notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message
to: ncep.list.enso-update@noaa.gov.

 

See the full report here.

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