Tropical Pacific warming patterns, winds hint at El Niño

At least one particular climatic condition that seems to influence weather conditions in the Northwest, as well as around the globe, has for the past year or more been stuck in neutral — the El Niño/Southern Oscillation index that considers sea surface temperatures and wind in the equatorial Pacific.

But conditions are changing with most prognosticators saying that a shift neutral conditions toward El Niño conditions as likely as not over the next several months. El Niño conditions generally tilt Northwest weather toward drier, warmer trends.

“An examination of monthly averaged temperature and precipitation values for El Niño versus La Niña years (1931-1999) in the PNW finds that El Niño winters tend to be warmer and drier than average. La Niña winters tend to be cooler and wetter than average,” according to the University of Washington-based Climate Impacts Group.

“The El Niño-Southern Oscillation (ENSO) remains neutral — neither El Niño nor La Niña,” according to Australia’s Bureau of Meteorology.

However, international climate models surveyed by the Bureau indicate that warming of the tropical Pacific is likely, with most models showing temperatures approaching or exceeding El Niño thresholds during the austral (southern hemisphere) winter, according to the Australian agency’s March 11 ENSO update.

“Recent observations indicate that warming of the tropical Pacific is occurring. The tropical Pacific Ocean sub-surface has warmed substantially over the past few weeks, which is likely to result in a warming of the sea surface in the coming months.

A recent burst of westerly winds over the far western Pacific is the strongest seen since at least 2009 – the last time an El Niño developed,” the bureau says. The warming SSTs and westerly winds are among the common signs attributed to the onset of El Niño conditions.

The SST anomaly map for February shows cooler-than-average SSTs in the eastern equatorial Pacific. Large areas of the surface waters of the western Pacific are warmer than average, extending from the area north of Indonesia and east of the Philippines to the South Pacific Convergence Zone well to the east of Australia.

NOAA’s Climate Prediction Center/NCEP/National Weather Service and the International Research Institute for Climate and Society on March 6 issued an “El Niño Watch” that mirrors the Australian assessment.

ENSO-neutral is expected to continue through the northern hemisphere spring 2014, with about a 50 percent chance of El Niño developing during the summer or fall,” the March 6 NOAA synopsis says.

ENSO-neutral continued during February 2014, with below-average sea surface temperatures (SST) continuing in the eastern equatorial Pacific and above-average SSTs increasing near the International Date, the synopsis says.

The model predictions of ENSO for this summer and beyond are relatively unchanged from last month. Almost all the models indicate that ENSO-neutral (Niño -3.4 index between -0.5°C and 0.5°C) will persist through the rest of the Northern Hemisphere spring 2014.

“While all models predict warming in the tropical Pacific, there is considerable uncertainty as to whether El Niño will develop during the summer or fall. If westerly winds continue to emerge in the western equatorial Pacific, the development of El Niño would become more likely,” the NOAA update says.

“However, the lower forecast skill during the spring and overall propensity for cooler conditions over the last decade still justify significant probabilities for ENSO-neutral.

“The consensus forecast is for ENSO-neutral to continue through the Northern Hemisphere spring 2014, with about a 50 percent chance of El Niño developing during the summer or fall….”

Columbia Basin Bulletin