Ed Dunham
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| (Former Meteorologist & CFHC Forum Moderator (Ed Passed Away on May 14, 2017)) |
| Sat Jul 10 2010 10:36 PM |
ENSO SST Trends vs Storm Totals
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I’ll start this with a re-post of an article from June12, 2007:
“About a month ago I did a little research from a slightly different angle. Since ENSO conditions are only available from 1950, I decided to check El Nino Region 3.4 anomalies against all of the very active seasons since 1950. I defined an active season as 14 named storms or more (there have been 10 of these) and ENSO neutral conditions as anything from +0.5C to -0.5C. I used the average sea surface temperature anomaly for the three month period of May, June and July (figuring that a three month lag was reasonable between Pacific ENSO conditions and Atlantic activity). The results coincide nicely with the findings of Ostro & Lyons.
1953...14 storms...+0.4 anomaly
1969...17 storms...+0.4 anomaly
1990...14 storms...+0.3 anomaly
1995...19 storms...+0.1 anomaly
1998...14 storms...+0.1 anomaly
2000...14 storms...-0.6 anomaly (weakening La Nina)
2001...15 storms...+0.1 anomaly
2003...15 storms.....0.0 anomaly
2004...15 storms...+0.4 anomaly
2005...28 storms...+0.3 anomalyâ€
Since that 2007 post, we can add 2007 and 2008 to the list (and they both continued the association of an ENSO neutral SST anomaly in May/June/July with high-activity seasons). Note that it does not mean that ENSO neutral conditions in M/J/J will always yield a high-activity season – it just means that previous high-activity seasons (since 1950) almost always occurred when ENSO neutral conditions (-0.5C to +0.5C) were observed at the beginning of the season.
2007…15 storms…-0.1 anomaly
2008…16 storms…-0.4 anomaly
A few months ago, the April/May/June ENSO SST anomaly was forecast to be 0.0C, but it came in at +0.3C. The May/June/July forecast was -0.5C but so far it looks like it will end up closer to -0.2C. The implication is that the upcoming La Nina event was overforecasted, i.e., too soon and too strong.
There is no previous season since 1950 that matches the current season SST anomaly to date, and the SST anomaly outlook for the remainder of the current season. 1998 is about the closest season for an SST trend except that 1998 started with a stronger El Nino and ended with a strong La Nina. The storm totals in 1998 were 14/10/3. 1970 somewhat matches the expected SST outlook for the remainder of this season and the storm totals in 1970 were 10/5/2, but 1970 did not start with a robust El Nino.
ED