This blog post is going to be on the second analogue I have made for Autumn 2018. The analogue is on Autumns during El Niño Modoki events. To start off, let me explain what El Niño Modoki actually is and how it differs from a classic El Niño event.
If you did not know what a classic El Niño is, it's when warming occurs in the eastern part of the equatorial Pacific i.e. El Niño Southern Oscillation (ENSO) regions 1+2. The below diagram shows you the ENSO regions of the equatorial Pacific. The warming has to involve sea surface temperature anomalies of at least +0.5°C above average over five tri-monthly periods (an example of a tri-monthly period being Jan-Feb-Mar).
Most of the time, this warming occurs in ENSO regions 1+2 but sometimes, you can have another type of El Niño. This type of El Niño is a "central based" El Niño or in Japanese, El Niño Modoki. With this type of El Niño, the warming is focused on the central part of the Equatorial Pacific i.e. ENSO region 3.4 (see diagram above). The diagram below compares the circulation of the classic El Niño and El Niño Modoki.
The long range models are forecasting an El Niño Modoki event to occur for 2018-19 but be aware that they can be very wrong. You don't need to go back far at all to find them wrong on this. Last year (2017) for example up to July, the models were showing an El Niño event to occur in the equatorial Pacific and it was looking likely that was going to happen due to the sea surface temperature anomalies but there is the Spring predictability barrier which makes ENSO forecasting extremely difficult and next to near impossible. As a result of these model forecasts, I have decided that the next Autumn 2018 analogue I will look at here is Autumns during El Niño Modoki events.
The 500mb height anomaly reanalysis from NOAA of El Niño Modoki Autumns shows very deep areas of below average heights to much of northern Europe and surrounding the Arctic Circle. There are above average heights over a lot of southern Europe reversely with the UK and Ireland (with the exception of northern Scotland) in between these main pressure centres with average heights. To me, this suggests a flat westerly Autumn with mild and unsettled conditions but not overly wet outside from northern Scotland. My first analogue for Autumn 2018 on warm Junes also suggested an unsettled Autumn but in quite a different way with the jet stream on a southerly track and northern blocking which this analogue does not show. Now let's see what the individual Autumns were like and look if we can see a trend towards what the overall reanalysis shows.
1979 - Wet up to the very north of the UK but otherwise dry and sunny in September though everywhere, it was a relatively cold month. October was wet in the north and west with above average sunshine and temperatures. November was very wet in Ireland and Scotland but fairly cool with some snow showers at times.
1986 - September was an extremely dry and cold but sunny month. It was one of the driest and coldest Septembers on record with the month being rainless in parts. October had close to average temperatures and fairly wet but sunny. November was mild and very wet everywhere with mostly sunny conditions.
1990 - September was wet over Scotland and North Wales but dry elsewhere; fairly cool. October was a very changeable, wet and mild month. November's temperatures were rather close to average with dry and sunny conditions in many places but the east of the UK was dull.
1991 - Early September continued a very warm spell that began at the end of August with some of the highest ever September temperatures being recorded in Ireland. After a fortnight, September became much more unsettled and cooler but it was a mild and sunny month overall. October was a cool and unsettled month whilst November was mainly dry but dull and fairly cool.
1992 - This was part of the warm Junes analogue so I'll post its summary here again. Fairly cold Autumn overall, largely down to one of the coldest Octobers of modern times (along with its following October in 1993). September was also relatively cool and wet whilst October was dry and November was mild but wet.
1994 - September was cool and wet. October had near average temperatures and fairly dry conditions. November was the mildest ever recorded with exceptional persistent warmth for the time of year but also dull and dry out from the far north of the UK and west of Ireland.
2002 - A very anticyclonic and dry September was in stark contrast to exceptional wet conditions for some through October and November resulting in severe floods such as in Dublin. It was Dublin's wettest November on record. October was on the cool side whilst September and November were relatively mild.
2004 - This was part of the warm Junes analogue so I'll post its summary here again. September started off very warm and sunny but soon became changeable after the first week with unsettled conditions prevailing. October was very wet and cool with a notable storm on the 27th/28th leading to severe flooding over the south and west of the UK and Ireland with Cork being especially suffered badly. November was very dull but also an exceptionally dry month with not a lot going on though it was rather cool out to the north and east of the UK with some wintry showers at times.
2009 - This was part of the warm Junes analogue so I'll post its summary here again. September was wet over Scotland with the northern part of Scotland having a soggy September in particular whilst the rest of the UK and Ireland had an anticyclonic month after an unsettled start. There was a notable drought for places from September 6th to October 6th. October had an unsettled blip near the start but otherwise, the first half continued on from the dry September though the second half was much more unsettled and mild throughout. November was extremely wet with record breaking floods and rainfall totals. It was the wettest November for a large portion of both countries and provided a stark contrast to the earlier part of the season.
So, we already have three years that have appeared in both Autumn 2018 analogues so far; 1992, 2004 and 2009. 2009 will make for an extremely interesting analogue year if it keeps appearing as one of the most common years for our Autumn 2018 analogues.
I think the signal from the warm Junes continues here that the Autumns tend to be on the unsettled side with these El Niño Modoki events with a particular emphasis either on October or November. September seems to be more settled with this set of analogues. Plenty more analogues to come though before we think of getting the Autumn 2018 forecast together for Tuesday, August 28th.
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