2021 Indicators: SST's / SAL / MSLP / Shear / Steering / Instability / Sat Images

[Hammy]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

[Category5Kaiju]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

Oddly enough, unlike 2013 or 2007, we are still getting NSs to form, and in those two years quantity was definitely a struggle. I honestly do not know and it’s a interesting thought, but to make things even more unclear, the Nina we are seeing now isn’t as comparable to 2013 or 2007 given it’s likely to be moderate and second year.

[Category5Kaiju]

Also interesting enough the current deep layer shear is pretty light in the GoM and WCAR, so thankfully there are no storms there now that can take advantage. Honestly, given we are about to see our 17th NS and are in for a season that will likely be a 20+ NS season, this actually got me wondering: while it was a small sample size, 2005 and 2020 were also very high NS count seasons, yet they lacked very frequent and intense MDR activity. Perhaps 2021 will be the same, and that there is some sort of trade off between high, 20+ NS count and high ACE, MDR hurricanes?

[aspen]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

If we see storms struggling due to anomalous shear in the Caribbean in mid-October when the VP setup and ENSO state suggests they should be bombing out, we’ll know something is up.

I will agree that Peter’s situation is strange. In any other September, it probably would be on its way to becoming a major, but now there’s a TUTT and dry air everywhere…in a developing Nina year.

[AlphaToOmega]

Also interesting enough the current deep layer shear is pretty light in the GoM and WCAR, so thankfully there are no storms there now that can take advantage. Honestly, given we are about to see our 17th NS and are in for a season that will likely be a 20+ NS season, this actually got me wondering: while it was a small sample size, 2005 and 2020 were also very high NS count seasons, yet they lacked very frequent and intense MDR activity. Perhaps 2021 will be the same, and that there is some sort of trade off between high, 20+ NS count and high ACE, MDR hurricanes?

That makes sense. MDR-heavy seasons tend to have weaker West African Monsoons than Western-Atlantic-based seasons. A strong West African Monsoon would create more vortices that could develop into tropical cyclones, but they would be competing in the MDR, leading to them developing farther west. A weak West African Monsoon would create fewer vortices, but there would not be as much competition, leading to them developing farther east.

[AlphaToOmega]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

There is a lot of sinking air due to a suppressive CCKW in the Atlantic. The fact that five storms have formed this month already should be significant. Once October comes, more intense hurricanes should form due to rising air in the Atlantic.

[Category5Kaiju]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

If we see storms struggling due to anomalous shear in the Caribbean in mid-October when the VP setup and ENSO state suggests they should be bombing out, we’ll know something is up.

I will agree that Peter’s situation is strange. In any other September, it probably would be on its way to becoming a major, but now there’s a TUTT and dry air everywhere…in a developing Nina year.

My personal take is that it’s the WPAC’s fault. Perhaps Chanthu did something, and the MJO currently favoring the WPAC is causing light shear in that basin currently while hurting the Atlantic? But then again, I also think it’s just bad luck, because if you look at the Atlantic’s current deep layer shear map, the WCAR and Gulf are in the green zones, and Peter just so happens to be in the wrong spot. Whatever the case I’m willing to bet that this unfavorable TUTT shenanigans is just temporary, because models really are confident that the end of this month will be a blast. Not to mention there’s nothing of significance forming in the WPAC or EPAC in spite of the below average WPAC shear for the foreseeable future.

[tolakram]

Background state is bad, for some reason, but weak storms still form. Potential is certainly there.

As an aside that may or may not be related, up here in Cincinnati we had a cold front wash out over us, with dew points in the 60's and no relief until later this week. This is NOT mid September weather. If the pattern is late, but ends up not being delayed once it unsticks (lol, deep meteorological smarts here) then we end up with less time for tropical activity, rather than simply a delay, we'll see.

[Ubuntwo]

Given the massive amount of shear and widespread PV streamers that are out there, I can't help wonder if there's something similar to 2013 with the ocean circulation going on (and similarly if this happened to some degree later in the 2007 season as well) or if there's some unknown factor specific to this sort of La Nina.

Ventrice strongly correlated convectively suppressed kelvin waves with the development of Atlantic TUTTs.

[Category5Kaiju]

Background state is bad, for some reason, but weak storms still form. Potential is certainly there.

As an aside that may or may not be related, up here in Cincinnati we had a cold front wash out over us, with dew points in the 60's and no relief until later this week. This is NOT mid September weather. If the pattern is late, but ends up not being delayed once it unsticks (lol, deep meteorological smarts here) then we end up with less time for tropical activity, rather than simply a delay, we'll see.

On the flip side the background state in the EPAC and WPAC are bad too; the EPAC has had less major hurricanes and storms than the Atlantic (and with Peter and potential future Rose, the Atlantic is definitely creeping up to catch up with the EPAC's ACE so far), and compared to what is typical, the WPAC's ACE is quite low, with only 2 super typhoons forming so far (and the WPAC has had less named storms than the EPAC). No foreseeable storms for the near future in the WPAC and EPAC, so one would have to think that either the Atlantic will become very dominant later this season, or all three basins are for some reason not performing well this year, the former of which I am more personally leaning on believing.

[AlphaToOmega]

I would say the reason the background state is bad simply because of a suppressive CCKW. In my opinion, this is a simple, logical explanation that fits the evidence: a lot of sinking air in the Atlantic. The one thing keeping September active in terms of storm count is the African Standing Wave. Come late September and October, the ECMWF, which is the most reliable model for intraseasonal variation, forecasts favorable CCKWs moving across the Atlantic, which would likely make conditions conducive for strong hurricanes.

[Iceresistance]

Background state is bad, for some reason, but weak storms still form. Potential is certainly there.

As an aside that may or may not be related, up here in Cincinnati we had a cold front wash out over us, with dew points in the 60's and no relief until later this week. This is NOT mid September weather. If the pattern is late, but ends up not being delayed once it unsticks (lol, deep meteorological smarts here) then we end up with less time for tropical activity, rather than simply a delay, we'll see.

Factor the Caribbean Sea can still produce Tropical Cyclones at late as Late November?

[Category5Kaiju]

IIRC, after Beta last year, wasn't there a suppressive MJO phase that prevented late September from being active and instead was devoid of any NSs? Perhaps we're experiencing something like that, albeit a bit earlier (meaning late September this year into October could be active, contrary to what we saw last year)

[kevin]

I know that to some this statement might seem like 'rephrasing your predictions until you're right at some point' (and maybe that is part of it ) since I also said that early September would be very active in terms of big storms, but I think that the last week of September and early October could be the the most active phase of this season. As others have pointed out I think the suppressive CCKW is an easy 1-on-1 explanation for the lack of activity. And usually when there is a simple explanation that fits all the boxes it's also the most likely one. And despite that we still got 4 (and soon 5) named storms in September, albeit weak storms. Since the Euro explicitly forecasts favorable CCKWs near the end of the month I think we could see a period with a similar pace in terms of storm formation, but where the storms that do form are way stronger than what we're seeing now. MDR trackers, while technically still possible this late (think of Inez, Flora, and Lili for example), are less likely so perhaps the WCar could become the hub for the strongest storms of the season just like what happened in 2020.

[jconsor]

Some insights into the lack of US landfalling hurricanes (along with no major hurricane landfalls) between 2006 and 2015, and the recent pronounced increase in US landfalling hurricanes.

 https://twitter.com/yconsor/status/1439581972137979908




 https://twitter.com/yconsor/status/1439583829535203332




 https://twitter.com/yconsor/status/1439585713260007424

[Iceresistance]

Does it seem like that the Buffer Zone only applies for Cape Verde (MDR) Hurricanes?

[Teban54]

Wild hypothesis: The amount of season cancel posts correlates with current activity, not potential activity.

There was a brief lull in season cancelling yesterday when 95L and 97L looked impressive for invests. Then they returned immediately today when they became naked swirls.

On a more serious note, this has been well-modeled in advance. We know a suppressed phase was bound to happen in mid-September, and we also know they will become more favorable in one or two weeks. I would reserve all 2013 calls until at least end of October.

[Category5Kaiju]

Wild hypothesis: The amount of season cancel posts correlates with current activity, not potential activity.

There was a brief lull in season cancelling yesterday when 95L and 97L looked impressive for invests. Then they returned immediately today when they became naked swirls.

On a more serious note, this has been well-modeled in advance. We know a suppressed phase was bound to happen in mid-September, and we also know they will become more favorable in one or two weeks. I would reserve all 2013 calls until at least end of October.

To be fair, 2013 should in no way serve as any comparison with this season given we have already had 6 hurricanes, 3 major hurricanes, and more NSs (and counting) with twice the ACE than that season ever had. I am honestly unsure about where this general idea of 2013 is suddenly coming from if you ask me.

[AnnularCane]

Wild hypothesis: The amount of season cancel posts correlates with current activity, not potential activity.

There was a brief lull in season cancelling yesterday when 95L and 97L looked impressive for invests. Then they returned immediately today when they became naked swirls.

On a more serious note, this has been well-modeled in advance. We know a suppressed phase was bound to happen in mid-September, and we also know they will become more favorable in one or two weeks. I would reserve all 2013 calls until at least end of October.

I also recall a lot of "season cancel" posts a couple days ago when 95L's percentages went down temporarily.

[aspen]

Wild hypothesis: The amount of season cancel posts correlates with current activity, not potential activity.

There was a brief lull in season cancelling yesterday when 95L and 97L looked impressive for invests. Then they returned immediately today when they became naked swirls.

On a more serious note, this has been well-modeled in advance. We know a suppressed phase was bound to happen in mid-September, and we also know they will become more favorable in one or two weeks. I would reserve all 2013 calls until at least end of October.

Are we sure conditions will become more favorable in that short of a time frame? I thought the suppressed MJO phase was supposed to peak at the end of September.