Could a major hurricane form outside the official bounds of the season?

[WalterWhite]

In the Atlantic, there has never been a recorded major hurricane outside the bounds of hurricane season. This makes sense, as typically, the Atlantic Ocean is too cold and/or wind shear is too high for such to occur. Could a major hurricane conceivably form after November 30 or before June 1, or is this too fantastic of a scenario to consider realistically?

[kevin]

This is the average temperature of the MDR (which, in this definition, also contains the Caribbean). If any MH forms in the Atlantic outside of the official bounds I expect it to be in the Caribbean since it usually has the highest SSTs in the Atlantic. Some of the most anomalous MHs since 1981 (the start of this database) are Eta (cat 4 in early November) Lenny (cat 4 in mid-November), Iota (cat 4 in mid-November), Beryl (cat 4 in June, cat 5 in July) and Otto (cat 3 in late November). If you look at the average SSTs of the MDR when each of those storms reached their peak you get.

Eta = 28.1C
Lenny = 27.2C
Iota = 28.0C
Beryl = 28.1C
Otto = 27.9C



Lenny is the only one of these storms to develop in regular MDR temperatures for that time of the year. In all other cases the MDR SSTs were way above normal for that time of year. Based on this small sample set I'd say average MDR SSTs of at least 27.9C are required for an MDR MH. I know this is just one piece of the puzzle, but if you use that and apply it to 2023 and 2024 you get the following time periods during which a MDR MH was possible. 2024 is following 2023 closely so the MDR temperature will probably also drop below 27.9C around early December. If we get more years similar to 2023 & 2024 or maybe even a bit more extreme then I'd say SSTs are sufficient for a MH in the MDR in the first week of December. However, the other pieces of the puzzle are moisture and shear which usually become very unfavorable outside of the season bounds. All in all, I'd say it's possible and we might see one sometime in the next 50 years. But even with the warming climate and higher SSTs I don't expect it to become a common occurrence.

2023 = June 6 - Dec 5
2024 = June 3 - present

[Cyclenall]

This is the average temperature of the MDR (which, in this definition, also contains the Caribbean). If any MH forms in the Atlantic outside of the official bounds I expect it to be in the Caribbean since it usually has the highest SSTs in the Atlantic. Some of the most anomalous MHs since 1981 (the start of this database) are Eta (cat 4 in early November) Lenny (cat 4 in mid-November), Iota (cat 4 in mid-November), Beryl (cat 4 in June, cat 5 in July) and Otto (cat 3 in late November). If you look at the average SSTs of the MDR when each of those storms reached their peak you get.

Eta = 28.1C
Lenny = 27.2C
Iota = 28.0C
Beryl = 28.1C
Otto = 27.9C

https://i.imgur.com/ztYHOWB.png

Lenny is the only one of these storms to develop in regular MDR temperatures for that time of the year. In all other cases the MDR SSTs were way above normal for that time of year. Based on this small sample set I'd say average MDR SSTs of at least 27.9C are required for an MDR MH. I know this is just one piece of the puzzle, but if you use that and apply it to 2023 and 2024 you get the following time periods during which a MDR MH was possible. 2024 is following 2023 closely so the MDR temperature will probably also drop below 27.9C around early December. If we get more years similar to 2023 & 2024 or maybe even a bit more extreme then I'd say SSTs are sufficient for a MH in the MDR in the first week of December. However, the other pieces of the puzzle are moisture and shear which usually become very unfavorable outside of the season bounds. All in all, I'd say it's possible and we might see one sometime in the next 50 years. But even with the warming climate and higher SSTs I don't expect it to become a common occurrence.

2023 = June 6 - Dec 5
2024 = June 3 - present

What I'm impressed by is how you gathered all this info together in 20 mins from when the topic was posted! I couldn't even write the post in that span let alone get the data then organize it with the TCs and their SST enviros. I wish I had that talent.

What are those date ranges for the current and last year? Is that when the SST value drops below what theoretical threshold for a major to be supported?

In terms of where exactly a MH in Dec could form, only a small area in the SWCAR near Panama and Costa Rica me thinks. I never tracked to see if the shear and dry air belt continue southwards into the central CAR though.

[kevin]

This is the average temperature of the MDR (which, in this definition, also contains the Caribbean). If any MH forms in the Atlantic outside of the official bounds I expect it to be in the Caribbean since it usually has the highest SSTs in the Atlantic. Some of the most anomalous MHs since 1981 (the start of this database) are Eta (cat 4 in early November) Lenny (cat 4 in mid-November), Iota (cat 4 in mid-November), Beryl (cat 4 in June, cat 5 in July) and Otto (cat 3 in late November). If you look at the average SSTs of the MDR when each of those storms reached their peak you get.

Eta = 28.1C
Lenny = 27.2C
Iota = 28.0C
Beryl = 28.1C
Otto = 27.9C

https://i.imgur.com/ztYHOWB.png

Lenny is the only one of these storms to develop in regular MDR temperatures for that time of the year. In all other cases the MDR SSTs were way above normal for that time of year. Based on this small sample set I'd say average MDR SSTs of at least 27.9C are required for an MDR MH. I know this is just one piece of the puzzle, but if you use that and apply it to 2023 and 2024 you get the following time periods during which a MDR MH was possible. 2024 is following 2023 closely so the MDR temperature will probably also drop below 27.9C around early December. If we get more years similar to 2023 & 2024 or maybe even a bit more extreme then I'd say SSTs are sufficient for a MH in the MDR in the first week of December. However, the other pieces of the puzzle are moisture and shear which usually become very unfavorable outside of the season bounds. All in all, I'd say it's possible and we might see one sometime in the next 50 years. But even with the warming climate and higher SSTs I don't expect it to become a common occurrence.

2023 = June 6 - Dec 5
2024 = June 3 - present

What I'm impressed by is how you gathered all this info together in 20 mins from when the topic was posted! I couldn't even write the post in that span let alone get the data then organize it with the TCs and their SST enviros. I wish I had that talent.

What are those date ranges for the current and last year? Is that when the SST value drops below what theoretical threshold for a major to be supported?

In terms of where exactly a MH in Dec could form, only a small area in the SWCAR near Panama and Costa Rica me thinks. I never tracked to see if the shear and dry air belt continue southwards into the central CAR though.

Thanks, I was just browsing the website and found the post exactly when it was posted and I was in a productive mood. Those date ranges are indeed the time when the average MDR SST value is at least 27.9C, which I used as a theoretical minimum temperature for a major hurricane. I'd also agree that any MH forming in December or late November would have to form all the way to the west in the WCar. Basically similar to Sara had that storm stayed away from land, preferably even a little further south.

However, all hurricanes that have formed in December so far are in the subtropics (the strongest was 80 kt, Olga in 2001). I highly doubt that a storm in this region could reach MH strength. Alice 1954 is the only December hurricane to partially track through the MDR, but this was in the eastern Caribbean. I don't know what is preventing storms from forming in the WCar in December, probably wind shear but I'm sure there are others on this forum with more knowledge in that regard. Either way, the WCar seems to be one of the few places in the NATL which can get high enough SST values in December to support a MH, so if we'll ever see one it'll probably happen there in unusually favorable background conditions, going through a period of RI just before landfall since it'll most likely form close to land. Probably something similar to hurricane Otto in 2016, just two weeks later in the calender year.