DorkyMcDorkface wrote:According to this chart, it technically qualifies as one,
but it's not a classic "EOF #1" signature. More like EOF #3, particularly in the western and far north Atlantic.
https://i.ibb.co/tpKxhk0/EAPS5y3-Xo-A0-Twdt.jpg Still, unlike the past two years, the subtropics aren't hogging most of the warmth this year.
Personally, when comparing the EOF chart to current SSTA in the basin, I would opine that this year seems more like a blend of EOF #2
and EOF #3. Note that the warmest SSTA in the far North Atlantic are displaced to the northeast of the British Isles, as is typical of EOF #2. Additionally, there are hints of cooler North Atlantic Deep Water (NADW) at the subsurface in the MDR, as even slightly-above-average easterlies quickly yield pockets of -SSTA, coupled with relatively warmer anomalies in the equatorial South Atlantic, near the Gulf of Guinea. Additionally, both EOF #2 and EOF #3 feature displaced warmth near the Bahamas and South Florida, to the north of the Greater Antilles.
All these features combined are more typical of a -AMO than a +AMO. However, the tropical Atlantic is far warmer than it typically is in a classic -AMO—possibly an artefact of climate change, which yields global rises in average SSTs, not just in the MDR, but also in the tropical North Pacific and the Indian Ocean. All in all, the absence of a “textbook” +AMO signature, along with conflicting signals in the Pacific, is a key reason as to why I would not forecast a hyperactive Atlantic season just yet. There are still many uncertainties about the location of forcing by ASO, with some indications that the Pacific may counteract the Atlantic, in terms of sinking air and shear over the Caribbean and western MDR. As I have posted previously, while cool neutral ENSO can yield above-average seasons just like La Niña,
history shows that most of the biggest (top-ten) ACE-producing Atlantic seasons had weak Niña conditions in place by ASO:
Indeed. This would make a well-above-average Atlantic season quite improbable, as opposed to a near-to-slightly-above-average year, which is far more probable and realistic. Based on mean
MEI data for ASO,
seven of the top ten years for ACE (since 1950) featured La Niña for ASO (bolded). Clearly, so long as a +AMO in place, the stronger La Niña gets, the more intense a season peaks.1) 2005: -0.081
2)
1995: -0.731
3) 2004: +0.3075
4)
2017: -0.4965
5)
1950: -0.838
6)
1961: -0.5275
7)
1998: -0.841
8)
1999: -1.3805
9) 1969: +0.902
10)
1996: -0.536
SourceAdditionally,
Kaplan v2 SSTA data show that 1933 had a solid Niña in place by ASO, as did 1893. Only 1878 and 1887 featured neutral ENSO by ASO and still featured very high ACE indices, largely due to very strong, “textbook” +AMO signatures in place. (Similar “classic” +AMO signatures existed in 1893 and 1933, too, unlike in 2020 thus far.) So just about every hyperactive Atlantic season, ACE-wise, featured either La Niña or “classic” +AMO conditions (or both) by ASO. Years like 1969, 2004, and 2005 were exceptions, not the norm, among seasons with very high ACE. Since 2020 is not likely to feature either La Niña or a “classic” +AMO by ASO, based on historical precedent, it is highly unlikely to be a hyperactive year, either in terms of overall numbers or ACE. An above-average season? Very likely. Hyperactive? Highly unlikely. Of course, even well-below-average seasons can be quite destructive, as activity is only loosely correlated with landfall(s) and impact(s), if at all, as 1992 and 2010, each an opposing extreme, amply illustrated. However, the facts should be clear that it is probably still premature to start comparing 2020 to 1933, 2005, and other hyperactive luminaries. (I would also wish to add that, if activity is concentrated in the eastern MDR in 2020, then the eastward displacement of development makes landfalls less likely, barring favourable steering currents. Interestingly,
wxman57 apparently is
channeling 2013 as an analog.)
