The National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) continue to call for the Pacific Ocean to have El Nino conditions during the coming 2018-19 winter season.
"All four Nino regions showed increased sea surface temperature (SST) anomalies in October. Positive subsurface temperature anomalies (averaged across 180 to 100 West Longitude) also continued, due to the persistence of above-average temperatures at depth across the eastern half of the equatorial Pacific Ocean," the CPC noted in an update issued Thursday, November 8. "El Nino is expected to form and continue through the Northern Hemisphere winter 2018-19 (approximately 80% chance) and into spring (55% to 60% chance)."
The atmospheric feature of El Nino, however, has still not truly engaged to coincide with the warming sea surface and subsurface temperatures.
"Atmospheric convection (cloud and thunderstorm development) remained slightly suppressed near the Date Line and over Indonesia," the briefing said. "Low-level westerly wind anomalies were observed over the eastern Pacific during October, while weak upper-level westerly wind anomalies were present over the far western Pacific. The traditional and equatorial Southern Oscillation indices (SOI) were near zero. Despite the above-average ocean temperatures across the equatorial Pacific Ocean, the overall coupled ocean-atmosphere system continued to reflect ENSO-neutral."
The takeaway from this discussion is the perspective that the oceanic wind pattern will, at some point, reflect the warming of the equatorial waters.
"The majority of models in the IRI/CPC (International Climate Research Institute/Climate Prediction Center) plume predict a Nino 3.4 index of +0.5-degree C or greater to continue through the rest of the fall and winter, and into spring. The official forecast favors the formation of a weak El Nino, with the expectation that the atmospheric circulation will eventually couple to the anomalous equatorial Pacific warmth," the CPC bulletin concluded.
As noted in a previous article and blog, DTN's winter forecast for 2018-19 expects the upcoming weak El Nino to have much less influence on the atmosphere this winter than this feature would otherwise. Thus, periodic bursts of colder air from the northern latitudes (the Polar Vortex), are considered to be more likely over the central part of the country. This differing forecast also looks for less precipitation in the western U.S. than would be the case if El Nino truly asserted its influence on the winter weather scene. Forecasts from the United Kingdom and the European Center for medium and long-range weather forecasting also have winter forecasts out that are more in line with DTN's look at the season versus the Climate Prediction Center's forecast.
Bryce Anderson can be reached at email@example.com
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