Synopsis: ENSO-Neutral conditions are slightly favored (between 55-60%) during the upcoming Northern Hemisphere fall and winter 2016-17.
ENSO-Neutral conditions were observed over the past month, although sea surface temperatures (SSTs) were below-average over the east-central equatorial Pacific Ocean. While the Niño-3.4 and Niño-3 regions remained around -0.5°C for most of the month, Niño-4 and Niño 1+2 were -0.1°C and +0.3°C, respectively, by the end of the month. Subsurface temperatures across the eastern and central Pacific remained below average, and negative temperature anomalies remained weak across the western Pacific. Atmospheric anomalies over the tropical Pacific Ocean largely indicated ENSO-Neutral conditions. The traditional Southern Oscillation index and the equatorial Southern Oscillation index were weakly positive during August. The lower-level winds were near average, while the upper-level winds were anomalously westerly in a small region to the east of the International Date Line. Convection was suppressed over the western and central tropical Pacific, although less suppressed compared to last month. Overall, the combined ocean and atmosphere system continues to reflect ENSO-Neutral.
The multi-model averages favor borderline Neutral-La Niña conditions (3-month average Niño-3.4 index less than or equal to -0.5°C) during the Northern Hemisphere fall, continuing into winter. However, the more recently updated model runs from the North American Multi-Model Ensemble (NMME) more strongly favor ENSO-Neutral. The forecaster consensus prefers this outcome, which is supported by the lack of significant anomalies in several indicators over the past month (winds, convection, subsurface temperatures). Overall, ENSO-Neutral conditions are slightly favored (between 55-60%) during the upcoming Northern Hemisphere fall and winter 2016-17.
All four states should be moderately to considerably warmer than normal for the month. All the plains States from Canada to Texas and across the Florida and up into the northeast should be slightly to moderately warmer than normal.
Most of Washington and Oregon should be normal to only slightly drier than normal. Most of California and Nevada should be slightly wetter than normal. For most of southern California and western Nevada this a very dry month and slightly wetter conditions will still mean that it will be a dry month. The upper plain states and upper Midwest should be moderately drier than normal along with the eastern seaboard and Ohio valley. Southern Florida should be slightly wetter than normal and the gulf states slightly direr than normal. However there is always the risk that hurricane and tropical depression rainfall could impact on local situations and exceed the longer term monthly forecast.