2025-2026 ENSO

[40/70 Benchmark]

17 hours ago, raindancewx said:

If you use the seasons above that finish at 0-40 ACE for Sept (I doubt it will be that high or that low but 20 seems about right with some activity likely by month end), you end up with this much smaller group of La Nina seasons.

1942 (9.9 Sept)

1956 (9.4 Sept)

2007 (29.0 Sept)

2016 (27.3 Sept)

Those are your 30-50 ACE June-Aug, with 0-40 ACE Sept La Nina years. Can narrow down more as September finishes. Very cold in the North & West in January of those years, fairly cold in December & March too. Feb very warm. As a reminder, 20 ACE would be a 100 kt sustained wind hurricane observation recorded at each of the six hour official advisory times...for five days in a row. Since 100 kts x 100 / 10,000 = 1 ace point (1 pt x 5 days x (24 hrs/6 hr space per observation) = 20). 

We may have the next Atlantic tropical storm in a day or two, but its already pretty far west to have a super long period as a major hurricane starting from nothing, if it develops. In a La Nina context, the 2017 September is useful anti-log - very low solar (we're very high now), very high activity September (175 ACE). You also had more of a classic hot West/cold East Summer (Jun-Aug) in 2017 which we didn't see this year.

High solar is probably weakly correlated to inactive hurricane seasons long-term. But its a little hard to tell as we haven't had a whole lot of super high solar years (July-June) in recent times with the Atlantic warmer. July 2024-June 2025 finished at 149 sunspots/month, but prior ~peaks/near peaks have been well over 200-250.

Those 4 seasons are all normal to slightly above normal snowfall around here.

[bluewave]

Record breaking rainfall with the impressive -IOD pattern.

La Niña in the modern climate

The Bureau of Meteorology has just changed the way it calculates sea surface temperature anomalies for monitoring La Niña (and El Niño).

Traditionally, sea surface temperatures inside the Niño 3.4 region were compared to the long-term average of the 30-year period from 1991 to 2020. The difference between the current temperature and the long-term average temperature gave us the anomaly used for monitoring La Niña.

However, rising global ocean temperatures caused by climate change have made this method ineffective. Put simply, Earth’s oceans are warming so quickly that the average ocean temperature of the past 30 years is cooler than the current global ocean temperature. This makes Niño 3.4 index values artificially warm when calculated using the traditional method.

Instead of comparing the current state of the ocean to a baseline from the past climate, scientists have developed a new method that also incorporates the current average temperature of the global tropical oceans. This new method, with is called the relative Niño index, removes the climate change signal from the equation and makes it more useful in our rapidly warming climate.
 

[snowman19]

Soil moisture very low across the entire Northeast and Mid-Atlantic

[40/70 Benchmark]

1 hour ago, bluewave said:

Record breaking rainfall with the impressive -IOD pattern.

 

La Niña in the modern climate

The Bureau of Meteorology has just changed the way it calculates sea surface temperature anomalies for monitoring La Niña (and El Niño).

Traditionally, sea surface temperatures inside the Niño 3.4 region were compared to the long-term average of the 30-year period from 1991 to 2020. The difference between the current temperature and the long-term average temperature gave us the anomaly used for monitoring La Niña.

However, rising global ocean temperatures caused by climate change have made this method ineffective. Put simply, Earth’s oceans are warming so quickly that the average ocean temperature of the past 30 years is cooler than the current global ocean temperature. This makes Niño 3.4 index values artificially warm when calculated using the traditional method.

Instead of comparing the current state of the ocean to a baseline from the past climate, scientists have developed a new method that also incorporates the current average temperature of the global tropical oceans. This new method, with is called the relative Niño index, removes the climate change signal from the equation and makes it more useful in our rapidly warming climate.
 

Mot of us have already been using this for a few seasons.

[bluewave]

The lower ACE this season than last year wasn’t that much of a surprise. All our 161+ ACE years since 2010 have seen a steep decline the following years.  

This year the record mid-latitude SSTs and cooling tropics are the main features creating the more stable conditions like we have been seeing more frequently in recent years.

So the direction lower this season for ACE is flowing the recent pattern. But magnitudes will be unique to each season. The amount of the decline can vary from year to year.

ACE step down pattern following 161+ seasons

2024….161….2025….39.3 so far

2020….180….2021…145…2022…94.4

2017….224….2018….132

 

 

[snowman19]

34 minutes ago, bluewave said:

The lower ACE this season than last year wasn’t that much of a surprise. All our 161+ ACE years since 2010 have seen a steep decline the following years.  

This year the record mid-latitude SSTs and cooling tropics are the main features creating the more stable conditions like we have been seeing more frequently in recent years.

So the direction lower this season for ACE is flowing the recent pattern. But magnitudes will be unique to each season. The amount of the decline can vary from year to year.

ACE step down pattern following 161+ seasons

2024….161….2025….39.3 so far

2020….180….2021…145…2022…94.4

2017….224….2018….132

 

 

If we finish this season below 100 ACE I for one will not be the least bit surprised 

[GaWx]

1 hour ago, snowman19 said:

If we finish this season below 100 ACE I for one will not be the least bit surprised 

 I sincerely hope it does end up <100. I’ve been directly significantly affected by 5 TS/H since 2016 and the US, overall, has been hit very hard. However, the two most recent Euro Weeklies means generate ~50 ACE over the next 4 weeks vs the 2005-24 avg of 40. If that were to verify, we’d be ~90 as of Oct. 12th with a high chance of reaching 100 by season’s end. For more details, folks can go to the Atlantic tropical thread if interested.

*Edit: I forgot to mention the favorable for TCG MJO consensus forecast dominating at least for the rest of Sept