When Pacific Ocean temperatures in the equator region hit a plus-3 degrees Celsius above-average figure in early August, and the ocean barometer reading known as the Southern Oscillation Index (SOI) came in at a minus 40 for a couple days, there was a strong feeling in the weather community that El Nino was truly flexing its muscle and was getting ready to indeed match the intensity of 1997-98.
However, there has not been a whole lot of follow-through from that point. Since that time, the ocean temperatures have basically flat-lined, and the SOI has shown trends away from rip-roaring El Nino conditions; in fact, the index had very weak (but still in the category) positive readings during a couple days in early September -- plus 2.35 on Sept. 2, and plus 7.55 on Sept 4.
Regarding the sea surface temperatures, their trends are not matching up well with the Hall-Of-Fame El Nino of 1997-98 either. My colleague DTN Senior Ag Meteorologist Mike Palmerino keeps a detailed log of the eastern Pacific SSTs -- a file that dates now almost 60 years back, to the early 1960s. At this point in the year, 2015 is not matching up that well with 1997.
Palmerino's numbers show these values for 1997 sea surface temperatures in the eastern Pacific for the late summer: July, plus 3.3; August, plus 3.8; September, plus 4.0; October, plus 4.5; November, plus 4.7; December, plus 4.8. (The preceding numbers are all departures from normal in degrees Celsius.)
Those are well-above-normal differences. And, they are warmer than we saw the Pacific this year so far. In July 2015, the eastern Pacific readings were plus 2.7 degrees Celsius above normal, and that departure stayed the same in August at plus 2.7 C. But back in 1997, July temperatures at plus 3.8 C were warmer than were noted this year, but also they were then followed by another increase by a half-degree Celsius in August to plus 3.8 C above normal, with further warming throughout the northern hemisphere fall into winter.
In contrast, the eastern Pacific Ocean readings appear to be leveling out, with August 2015 at plus 2.7 C staying the same as July 2015. That's still well above normal, but it's not suggestive of an ocean temperature pattern that continues to intensify on the warm side.
What this means for the Pacific as a whole is that the ocean temperature trend appears to be matching the forecast for El Nino as indicated by the Australia Bureau of Meteorology (BOM) -- with Pacific Ocean temperatures staying about where they area through the next several months, and then slowly retreating during spring 2016. That's a much different forecast than the U.S. forecast model, which has the water temperatures, and El Nino, continuing to get warmer until December, and then putting in a sharp cooling all the way to neutral values by late April 2016.
For U.S. agricultural weather, this more-sedate tone to the Pacific Ocean temperatures, SOI tendency, and the forecast also imply that weather patterns this fall may have more variability than indicated a few weeks ago.
That variability includes a higher chance for rain and harvest delays in the Midwest, and a more questionable prospect for the western U.S. to get much help from generous Pacific Ocean moisture.
There is a more indefinite tone to the 2015 El Nino prospect now than there was just one week ago.
Bryce can be reached at firstname.lastname@example.org
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