2018 Indicators: SST's / MSLP / Sal / Steering / Shear / Instability (Graphic updates at first post)

[storminabox]

Pretty steep drop:

What’s causing this?

[Ntxw]

Pretty steep drop:

https://i.imgur.com/E6Bhsqc.png

What’s causing this?

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

[NotSparta]

Pretty steep drop:

What’s causing this?

A speeding up of trades due to the MJO going into an even more unfavorable position for warming (along w/ CCKW influence), and a surge of below avg PWATs causing more evaporative cooling.

[WeatherEmperor]

Pretty steep drop:

https://i.imgur.com/E6Bhsqc.png

What’s causing this?

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

Here is a closer look at the NAO for the past few months showing a lot of positive as you mentioned.




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[Hurricaneman]

The 0zGFS show something trying to form in the Bahamas in the long range, most likely a phantom but does coincide with the upcoming CCKW moving into the Atlantic and I wouldn’t be surprised if something maybe even substantial forms between August 10th and 20th

[Eric Webb]

Pretty steep drop:

https://i.imgur.com/E6Bhsqc.png

What’s causing this?

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

The +NAO's correlation to MDR SSTAs degrades significantly during the summer because the wavelengths change dramatically, you can easily have a +NAO in the summer that still favors warming. The nearly 1C cooling in just the past few days seems strange considering that the trade winds only increased slightly (~0.5 m/s) and SAL isn't that extensive. Evaporative cooling from dry air is only real effective when you have preexisting convective downdrafts to mix that cooler air to the surface and there's hardly any convection to do that in the MDR and even then convection comprises a very small fraction of the total area of the MDR.

[Ntxw]

What’s causing this?

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

The +NAO's correlation to MDR SSTAs degrades significantly during the summer because the wavelengths change dramatically, you can easily have a +NAO in the summer that still favors warming. The nearly 1C cooling in just the past few days seems strange considering that the trade winds only increased slightly (~0.5 m/s) and SAL isn't that extensive. Evaporative cooling from dry air is only real effective when you have preexisting convective downdrafts to mix that cooler air to the surface and there's hardly any convection to do that in the MDR and even then convection comprises a very small fraction of the total area of the MDR.

Right. But it (NAO) is one part of a much larger picture. The Arctic-Far North Atlantic region has been under the influence of a persistent reverse dipole all summer, the strongest since 2013-2014. I would be surprised if that had no long term effects of spatial SSTs in the North Atlantic basin. When not getting help from the MJO, my assumption would be things revert back to the seasonal signal.

[Shell Mound]

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

The +NAO's correlation to MDR SSTAs degrades significantly during the summer because the wavelengths change dramatically, you can easily have a +NAO in the summer that still favors warming. The nearly 1C cooling in just the past few days seems strange considering that the trade winds only increased slightly (~0.5 m/s) and SAL isn't that extensive. Evaporative cooling from dry air is only real effective when you have preexisting convective downdrafts to mix that cooler air to the surface and there's hardly any convection to do that in the MDR and even then convection comprises a very small fraction of the total area of the MDR.

Right. But it (NAO) is one part of a much larger picture. The Arctic-Far North Atlantic region has been under the influence of a persistent reverse dipole all summer, the strongest since 2013-2014. I would be surprised if that had no long term effects of spatial SSTs in the North Atlantic basin. When not getting help from the MJO, my assumption would be things revert back to the seasonal signal.

I think this unusually rapid cooling of the SSTs may indicate that the subsurface in the tropical Atlantic has cooled significantly vs. 2017 and is likely the coldest since the last -AMO prior to 1995. Combined with the extremely cold subsurface in the far North Atlantic, the recent cooling in the MDR may indicate that the surface is increasingly sensitive to even the slightest external influence, owing to the very cold waters lurking in the thermocline. Therefore, I would venture to say that we may be seeing an indication that the +AMO since 1995 has officially ended, and we are entering into a very strong -AMO cycle. Arguably, the -AMO trend really took off in 2013, but there were already signs of a slowing AMOC (weakening THC) since the 1970s, and the Atlantic started to look more unfavourable, generally speaking, after 2005. Since much of the cooling in the tropical Atlantic is related to the cold far North Atlantic (North Atlantic Deep Water or NADW), which in turn is attributable to increased freshwater from Greenland due to climate change, it is possible that a warming global climate may have set in motion changes that nearly singlehandedly ended the +AMO of 1995-2012. Certainly, this +AMO appears to have been shorter-lived than any of the previous known ones. Honestly, I cannot recall such a cold tropical Atlantic in my lifetime, except prior to 1995. 2017 looks more and more like a blip in an otherwise clearly unfavourable trend for active Atlantic hurricane seasons.

[cycloneye]

A strong Kelvin wave is passing the tropical Atlantic, likely to give the West African Monsoon a boost in the coming days.

 https://twitter.com/MJVentrice/status/1022099833300180994

[Eric Webb]

The persistent +NAO of the past 3-4 months. There have been dips negative but they have been brief and not sustaining. Also the cold waters below the surface are deep. When the MJO is favorable there also tends to be periods of warming but that is shorter periods than seasonal scale.

The +NAO's correlation to MDR SSTAs degrades significantly during the summer because the wavelengths change dramatically, you can easily have a +NAO in the summer that still favors warming. The nearly 1C cooling in just the past few days seems strange considering that the trade winds only increased slightly (~0.5 m/s) and SAL isn't that extensive. Evaporative cooling from dry air is only real effective when you have preexisting convective downdrafts to mix that cooler air to the surface and there's hardly any convection to do that in the MDR and even then convection comprises a very small fraction of the total area of the MDR.

Right. But it (NAO) is one part of a much larger picture. The Arctic-Far North Atlantic region has been under the influence of a persistent reverse dipole all summer, the strongest since 2013-2014. I would be surprised if that had no long term effects of spatial SSTs in the North Atlantic basin. When not getting help from the MJO, my assumption would be things revert back to the seasonal signal.

I did not say nor imply that the behavior of the NAO in the summer has no effect on SST in the North Atlantic basin but you can't just assume the same pattern/forcing in the winter that favors cooling in the MDR will lead to the same result in the summer, that's a terrible assumption because the wavelengths are really short at this time of the year.

[Ntxw]

We are not discussing the winter pattern, my reference was to the past 3-4 months as a possible reason to the previous poster's question. If that is not correct in your views then by all means present them as to their question.

[BigAndBendy]

Can’t help but feel like this steep of a cooling event is the result of many factors, some of which aren’t even currently known / understood.

[Eric Webb]

:uarrow: We are not discussing the winter pattern, my reference was to the past 3-4 months as a possible reason to the previous poster's question. If that is not correct in your views then by all means present them as to their question.

It's blatantly obvious we're not discussing the winter pattern but you gave the +NAO as a reason to the recent MDR cooling because you made the invalid assumption that the +NAO in both summer and winter cools the MDR and that's simply not true.

[Ntxw]

:uarrow: We are not discussing the winter pattern, my reference was to the past 3-4 months as a possible reason to the previous poster's question. If that is not correct in your views then by all means present them as to their question.

It's blatantly obvious we're not discussing the winter pattern but you gave the +NAO as a reason to the recent MDR cooling because you made the invalid assumption that the +NAO in both summer and winter cools the MDR and that's simply not true.

Like I said, if that is not correct, then present your thoughts to the poster and we can discuss it. No need to get worked up here.

[Eric Webb]

:uarrow: We are not discussing the winter pattern, my reference was to the past 3-4 months as a possible reason to the previous poster's question. If that is not correct in your views then by all means present them as to their question.

It's blatantly obvious we're not discussing the winter pattern but you gave the +NAO as a reason to the recent MDR cooling because you made the invalid assumption that the +NAO in both summer and winter cools the MDR and that's simply not true.

Like I said, if that is not correct, then present your thoughts to the poster and we can discuss it. No need to get worked up here.

The poster is wholly capable of reading my responses to you and any other exchanges on this forum. Here's the actual z500 correlation plots for both July and January so you can see how messy things become in the summer w/ a stronger than normal Icelandic vortex in July favoring warming yet a more significant blocking ridge is present over Iceland in January and leads to the same result.


July z500 AMO correlation



January z500 AMO correlation

[Ntxw]

That'll bring me to the same question as the prior poster. What is causing then of the recent drop? Perhaps erroneous satellite data?

[Eric Webb]

That'll bring me to the same question as the prior poster. What is causing then of the recent drop? Perhaps erroneous satellite data?

It's possible there's some error in data assimilation or noisy satellite data (data assimilation is in the CDAS acronym after all), I just have a hard time believing the MDR could have cooled almost 1C with near average trades and relatively more modest SAL in just a matter of a few days, the cumulative effect of stronger trades in July, a cold subsurface, and some SAL when the MDR is already cold certainly doesn't help and could explain some of this drop but it's so extreme in such a short period of time I'm personally skeptical it's actually real.

[NotSparta]

That'll bring me to the same question as the prior poster. What is causing then of the recent drop? Perhaps erroneous satellite data?

It's possible there's some error in data assimilation or noisy satellite data (data assimilation is in the CDAS acronym after all), I just have a hard time believing the MDR could have cooled almost 1C with near average trades and relatively more modest SAL in just a matter of a few days, the cumulative effect of stronger trades in July, a cold subsurface, and some SAL when the MDR is already cold certainly doesn't help and could explain some of this drop but it's so extreme in such a short period of time I'm personally skeptical it's actually real.

[img]https://www.tropicaltidbits.com/analysis/ocean/mdrssta.png[img]


[img]http://www.atmos.albany.edu/student/ventrice/real_time/timeLon/u.anom.30.10N-20N.gif[img]

I'm seeing a lot of artifacts in the data, that would push down the index a lot erroneously

[Eric Webb]

You can get the hint that the 3 sigma CCKW passing over the Atlantic has reached west Africa.




On a somewhat related note, I really like this vertical cross section forecast plot from wxnerds. You can see the CCKW influence helping to moisten the MDR for the first few days of the forecast period then a subsequent dry period once it passes and then moistening near the level of the AEJ (~600-700 hPa) as AEWs triggered by the CCKW propagate into the Atlantic the following week.

[HurricaneEnzo]

You can get the hint that the 3 sigma CCKW passing over the Atlantic has reached west Africa.

Wow is that top image accurate or something wrong with the satellite? I don't know that I've ever seen that much convection over Africa like that lol.