NOAA Downgrades Probability Of 2017 El Nino

[rangerrebew]

NOAA Downgrades Probability Of 2017 El Nino

    Date: 12/05/17
    NOAA Climate Prediction Center

NOAA has downgraded the probability of an El Nino later this year to 46% from 51% in its April forecast and 53% in March.

ENSO-neutral persisted during April, with near-average sea surface temperatures (SSTs) observed across the central equatorial Pacific and above-average SSTs in the eastern Pacific [Fig. 1]. The latest weekly Niño index values were +0.5°C in the Niño-3 and Niño-3.4 regions, and +0.3 and +0.8°C in the Niño-4 and Niño-1+2 regions, respectively [Fig. 2]. The upper-ocean heat content anomaly was slightly positive during April [Fig. 3], reflecting the strengthening of above-average temperatures at depth around the Date Line [Fig. 4]. Atmospheric convection anomalies were weak over the central tropical Pacific and Maritime Continent [Fig. 5], while the lower-level and upper-level winds were near average over most of the tropical Pacific. Overall, the ocean and atmosphere system remains consistent with ENSO-neutral.

Most models predict the onset of El Niño (3-month average Niño-3.4 index at or greater than 0.5°C) during the Northern Hemisphere summer [Fig. 6]. However, the NCEP CFSv2 and most of the statistical models are more conservative and indicate that while Niño-3.4 index may be near or greater than +0.5°C for several months, the warmth may not last long enough to qualify as an El Niño episode (5 consecutive overlapping seasons) and/or may not significantly impact the atmospheric circulation. Relative to last month, the forecaster consensus reflects slightly lower chances of El Niño (~45%), in part due to the conflicting model guidance and lack of a clear shift toward El Niño in the observational data. In summary, while chances are slightly lower than 50%, ENSO-neutral and El Niño are nearly equally favored during the Northern Hemisphere summer and fall 2017 (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).
Full post

 http://www.thegwpf.com/noaa-downgrades-probability-of-2017-el-nino/

[thackney]

https://www.climate.gov/enso

El Niño:  A warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean.  Over Indonesia, rainfall tends to become reduced while rainfall increases over the tropical Pacific Ocean.  The low-level surface winds, which normally blow from east to west along the equator (“easterly winds”), instead weaken or, in some cases, start blowing the other direction (from west to east or “westerly winds”).

La Niña: A cooling of the ocean surface, or below-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean.  Over Indonesia, rainfall tends to increase while rainfall decreases over the central tropical Pacific Ocean.  The normal easterly winds along the equator become even stronger.

Neutral:  Neither El Niño or La Niña. Often tropical Pacific SSTs are generally close to average.  However, there are some instances when the ocean can look like it is in an El Niño or La Niña state, but the atmosphere is not playing along (or vice versa).