Originally Posted by sryanbruen
An active Atlantic hurricane season is one of the things we look at for Winter as it dumps a lot of warm water in the North Atlantic Ocean which can then be advected into the North Pole and promote northern blocking. 2010 was an active hurricane season. 1995 was an active hurricane season. 1887 was an active hurricane season. These are three examples of years that had active hurricane seasons and were followed by cold winters. However, it's not impossible to receive a cold Winter with an inactive hurricane season, 2009 was such an example and was followed of course by 2009-10. 2009-10 was an a moderate El Nino Modoki and as a result had increased vertical wind shear which led to the inactive hurricane season but as it was El Nino Modoki, we had a cold Winter. El Nino Modoki is very good for cold Winters in the UK and Ireland! The El Nino which is forecast by the models and agencies this year is a modoki and I expect it to be a modoki but there is uncertainty on if it will reach El Nino threshold which is 0.5c or more above average. 1990-91 was an El Nino Modoki but did not reach the threshold though it was a cold Winter with a notable cold and snowy spell in early February 1991. Anyway, I'm going off on a bit of a tangent, thought you'd might like that extra info with this post.
The SST profile in the Atlantic we want to see is one like this from 14 December 2009, bands of warm-cold-warm. What is the least favourable for a negative NAO in our current SST profile is the cold anomalies to the south of Greenland, we would want to see them disappear by Winter time and not to mention, the warm anomalies off the coast of America. They are two problems with the current state of the North Atlantic which are not favourable for negative NAO especially with a more powerful Polar Vortex as Winter gives. Things can change like they have since May as the Atlantic is more favourable now than it was in May but it's getting kind of late especially as it takes quite a bit of time for the temperatures in the North Atlantic to change unlike say the Irish Sea or the North Sea. Nevertheless, in spite of 1976 being similar to 2018 in terms of the Atlantic SST profile, 1976-77 was a cold Winter with a cold December and January but mild February.
As described in the quote above, an active hurricane season is one of the things we look at for the Winter season solely for the fact that:
1. It dumps a lot of warm water in the Atlantic Ocean. The warm air is advected into the Arctic to promote northern blocking. During Winter time pre-cold spells, you'll hear "warm air advection" mentioned a lot of the time which is what happened before the beast from the east in February 2018 as high pressure built to the east against the Atlantic. The battle of two brought winds into the south which whilst cold on the surface had warm 850hPa temperatures being advected up to the pole where the southerly winds were pointed at. This gave away to cold air being shunted out the other side of the anticyclonic block over Scandinavia and via easterly winds (helped by SSW) came to us.
2. The warm tropics form one band of the North Atlantic tripole which is explained in the quoted post.
This table I have made categorises different Atlantic hurricane seasons from 1914 to 2017 based on the number of storms that occurred. Some maybe swapped to other categories but I think I categorised the seasons well for analogues. I have highlighted in yellow the hurricane seasons that preceded really cold Winters or Winters that contained a notable snowy/cold spell at some stage.
As you can see, there's actually quite a mix to be seen here. 16 inactive seasons preceded such Winters, 5 average seasons preceded such Winters, 13 active seasons preceded such Winters whilst 6 very active seasons preceded such Winters. The latter is notable because there's only 9 examples of very active seasons in this sample space and 2/3 of them seasons were followed by such Winters. Another very active season that comes to mind is 1887 which was followed by a cold Winter.
1978, though ended up average overall (very active during the Autumn of 1978), was very quiet in terms of Atlantic tropical cyclones pre-September with little activity going on. Let's compare the Atlantic SST profiles of May 1978 and May 2018.
They have some similarities like the main development region (MDR) for Atlantic hurricanes by Cape Verde near Africa was cold in both years. The Gulf of Mexico is warm in both years. However, in 1978, the eastern seaboard in the US had much colder waters and same with the Norwegian Sea. 1978's Atlantic SST profile is rather close to a tripole unlike May 2018.
The models are picking up on at least 3 tropical cyclones to develop in the next 14 days in the Atlantic Ocean. Why is this happening suddenly after a quiet start to the season? Well we're coming up to when the season usually peaks in terms of developments and also, the main development region has significantly warmed up since May as shown by the graph below given by Levi Cowan. This doesn't look like anything big given the anomaly is close to average but it is a major difference to the potential for tropical developments in the Atlantic Ocean.
As you know, the sea surface temperatures in the Atlantic Ocean are one of the biggest issues this year so far for the coming Winter but maybe tropical developments coming up will make a little difference in that.
If El Nino does occur, vertical wind shear will increase and the Atlantic hurricane season will continue to be quiet. However, I am getting more and more skeptical about the chances of El Nino occurring this year with the models being biased to warmth. There is still little sign from the ocean right now for El Nino to occur and if one does occur, it's likely to be weak which is the kind of ENSO event apart from neutral that has little impact on the atmosphere unlike say a very strong El Nino that last occurred in 2015-16.