ASLR, thank you for updates (and for including the parenthesis for us newbie amateurs). Question: For an El Niño to be officially declared, there must be stable values for eg NDJ — November — December — January — ie a 3–month period, right? So the earliest official start of the 2014/15 El Niño will be in November, or in January?
Edit: So is OND, NDJ, DJF, JFM, FMA the earliest possible start, or must every day exceed +0.5?
Viddaloo,
The following link leads to an article written back in late May by Michelle L'Heureux who is one of the main authors of NOAA's climate.gov ENSO blog. This article briefly covers matters such as the ONI, SOI, and El Niño “events” versus El Niño “conditions”. There are many other links provided throughout the article, which lead to other interesting blog posts and information about all things ENSO. I would highly recommend checking it out.
Link to article from NOAA's ENSO blog:
http://www.climate.gov/news-features/blogs/enso/how-will-we-know-when-el-ni%C3%B1o-has-arrivedAlso, I agree with ASLR's reply #1811. If SSTA in the Nino 3.4 region continue to stay at or above +0.5 deg c from now until at least mid April 2015, then by early May 2015, when the FMA ONI value is issued, we'll be able to look back at the historical ONI values and see that this El Nino officially started during the OND 3 month season of 2014. Again, that's only if SSTA in the Nino 3.4 region continue to stay at or above +0.5 deg c from now until at least mid April 2015 (SIDE NOTE: typically the SSTA in the Nino 3.4 region can NOT stay above the +0.5 deg c El Nino thresh hold for 5 consecutive 3 month seasons without an ocean-atmosphere coupling. This is why the ONI is such an important tool for declaring out and out El Nino events). If not OND then NDJ, but that would be outside the historical norm for weak El Nino events based on ONI data. I guess anything is possible though, right? If the 2014 El Nino starts during the NDJ 3 month season then we wouldn't know for sure until the MAM ONI value is issued in June 2015. However, trust and believe that we'll know whether or not an El Nino event is under way long before the ONI data "officially" says so. This would be due to changes in many of the following: the walker cell, trade winds, equatorial ocean surface currents, the North Pacific jet stream configuration/storm track, SOI values, Sea level anomalies, number/strength/position of tropical cyclones in the Eastern Pacific vs. the Atlantic, strength of the MJO, OLR, tropical and subtropical weather patterns, equatorial subsurface temp anomalies, and of course SSTA across the equatorial Pacific. As El Nino begins to take root, weak, moderate, or strong changes will begin to occur in much of the ENSO indicators that i just listed, signaling that El Nino is underway (there are other ENSO indicators and I'm sure ASLR could add to the list). Some of these changes already appear to be underway. Such as the way above avg hurricane season in the Eastern Pacific (which has been the most active since 1992) vs. the just slightly below avg hurricane season in the Atlantic, the SOI, Equatorial Pacific SSTA, Equatorial Pacific subsurface anomalies, North Pacific storm activity and the re-curving of multiple TC's in the Western Pacific, and lack of any sustained/strong easterly trade winds (just patches here and there, but overall weaker than normal with a slight bias towards weak westerly anomalies according to TAO data). I'm probably even leaving a few things out. (ANOTHER SIDE NOTE: being a surfer from So Cal, I can verify that storm activity in the gulf of Alaska has been above avg with 3 Major North Pacific storm swells hitting the US west coast so far this Fall (still a weak ridge of high pressure blocking So Cal from rain, but storm activity in the N PAC is a bit above normal. Rain is actually in the forecast for much of CA by Saturday Nov 1st. Fingers crossed). Last year we didn't see our first Major swell until Thanksgiving day. Also, former Hurricane Ana of the Central Pacific re-curved back towards North America and her post-tropical remnants are now making landfall over Canada and the Pacific Northwest. Not normal for a TC to go from the Central Pacific to the Pacific Northwest, but has happened during El Nino years. Namely hurricane Guillermo of 1997).