2020 Indicators: SST's / SAL / MSLP / Steering / Shear / Instability / Sat Images

[toad strangler]

You are incorrect, you didn't finished reading when SAL peaks, "Saharan Air Layer activity usually ramps up in mid-June, peaks from late June to mid-August,
and begins to rapidly subside after mid-Augustt". So in another words in average July is when is at its worst, proven by previous years. And by the way things look it could very well continue to through July.

https://www.weather.gov/media/zhu/Sahar ... _Plume.pdf

I think we are splitting hairs here and I wouldn't state that I'm incorrect. The last 17 years have had SAL peak average in late June. Post #1161 in this thread. Also, I have previously mentioned that SAL can easily reign through July and even the first half of August. There would be nothing abnormal about that.

So why would you say that "SAL peaks in late late June and that it tails off throughout July" is either A or B, make up your mind

Look at the chart I posted. It tails off. Just like hurricane activity does post September 10th. Does that mean there can't be huge activity afterward? Of course not. I'd say you are missing context by a large margin.

[NDG]

I think we are splitting hairs here and I wouldn't state that I'm incorrect. The last 17 years have had SAL peak average in late June. Post #1161 in this thread. Also, I have previously mentioned that SAL can easily reign through July and even the first half of August. There would be nothing abnormal about that.

So why would you say that "SAL peaks in late late June and that it tails off throughout July" is either A or B, make up your mind

Look at the chart I posted. It tails off. Just like hurricane activity does post September 10th. Does that mean there can't be huge activity afterward? Of course not. I'd say you are missing context by a large margin.

I think the chart is meant to show that the peak is July, not late June, because everything that I have read says that the peak of SAL is during the month of July. I have asked Michael Lowry.

[toad strangler]

So why would you say that "SAL peaks in late late June and that it tails off throughout July" is either A or B, make up your mind

Look at the chart I posted. It tails off. Just like hurricane activity does post September 10th. Does that mean there can't be huge activity afterward? Of course not. I'd say you are missing context by a large margin.

I think the chart is meant to show that the peak is July, not late June, because everything that I have read says that the peak of SAL is during the month of July. I have asked Michael Lowry.

https://i.imgur.com/Mc8ECI3.jpg

July is definitely in the SAL peak period for sure. I was referencing late June as THE peak as in we reference Sept 10th as THE peak of hurricane season. That's where we crossed wires lol. All good discussion.

[NDG]

Look at the chart I posted. It tails off. Just like hurricane activity does post September 10th. Does that mean there can't be huge activity afterward? Of course not. I'd say you are missing context by a large margin.

I think the chart is meant to show that the peak is July, not late June, because everything that I have read says that the peak of SAL is during the month of July. I have asked Michael Lowry.

https://i.imgur.com/Mc8ECI3.jpg

July is definitely in the SAL peak period for sure. I was referencing late June as THE peak as in we reference Sept 10th as THE peak of hurricane season. That's where we crossed wires lol. All good discussion.

That's where we disagree, you say late June I say near the middle of July, as the Sept 10th of the peak of the hurricane season

[USTropics]

It's definitely not a hard date (i.e. every year on July 15th we'll be at peak SAL for the season). You have to find the root component. What has the biggest influence on SAL propagation? Pressure gradient changes between seasonal positions of the ITCZ:


What influences the ITCZ wanting to lift north? SSTA temperature differences between northern/southern Atlantic:


Given the current SSTA configuration and current ITCZ location relative to climo, we should be seeing a typical peak sometime between now and mid/late July:


Most likely the next suppressed passage (mid-late July) will once again promote increased easterlies in the upper atmosphere, which is typically when we see the most extensive SAL outbreaks:

[Shell Mound]

According to data from ESRL’s NCEP/NCAR SST reanalysis, the AMO in June ‘20 has been cooler than in June ‘17, owing to greater North Atlantic Deep Water (NADW) penetration. This is why slight changes in the synoptic pattern produce significant ± fluctuations in SSTs across the North Atlantic basin, given the presence of very cold subsurface waters in the eastern subtropics and far North Atlantic. I’m still uncertain as to whether cool neutral ENSO and a strong WAM/AEJ will be sufficient to overcome the rather anaemic state of the AMO. The AMO, to me, is the biggest potential negative factor that could hinder the 2020 Atlantic hurricane season, not the SAL. Only one and a half week of ridging over the Northwestern Atlantic has been sufficient to eliminate well-below-average SSTs and build a massive warm pool off New England and the Mid-Atlantic region—a feature that is typical of a -AMO regime. This means that the subsurface over the Northwestern (Northeastern) Atlantic is very warm (cold) and easily reaches the surface as soon as low-level winds slacken (strengthen) and veer (back). I would pay more attention to the subsurface than the surface when gauging the state of the AMO. Even if the MDR/Caribbean have been mostly above average for most of June, the preponderance of cold NADW in the eastern subtropics/far North Atlantic means that as soon as trade winds strengthen, virtually all the warm SSTs vanish, as they have in just the past week. Now SSTs in the MDR/Caribbean are average to below average at best.

[SFLcane]

Look at the chart I posted. It tails off. Just like hurricane activity does post September 10th. Does that mean there can't be huge activity afterward? Of course not. I'd say you are missing context by a large margin.

I think the chart is meant to show that the peak is July, not late June, because everything that I have read says that the peak of SAL is during the month of July. I have asked Michael Lowry.

https://i.imgur.com/Mc8ECI3.jpg

July is definitely in the SAL peak period for sure. I was referencing late June as THE peak as in we reference Sept 10th as THE peak of hurricane season. That's where we crossed wires lol. All good discussion.

It never fails every year we get bouts of SAL around this time of the year it generally peaks around mid July but yet the thread is flooded with season cancel posts only to see 5-6 storms develop in Aug. Patience grasshoppers

[toad strangler]

I think the chart is meant to show that the peak is July, not late June, because everything that I have read says that the peak of SAL is during the month of July. I have asked Michael Lowry.

https://i.imgur.com/Mc8ECI3.jpg

July is definitely in the SAL peak period for sure. I was referencing late June as THE peak as in we reference Sept 10th as THE peak of hurricane season. That's where we crossed wires lol. All good discussion.

It never fails every year we get bouts of SAL around this time of the year it generally peaks around mid July but yet the thread is flooded with season cancel posts only to see 5-6 storms develop in Aug. Patience grasshoppers

I haven't seen one cancel post of any kind.

[USTropics]

A very informative article by Jeff Masters (https://www.yaleclimateconnections.org/ ... n-decades/) was posted last night regarding SAL and its effects on the recent MDR cooling (-0.4C average). As we thought, this was quite a historic SAL outbreak:

[toad strangler]

A very informative article by Jeff Masters (https://www.yaleclimateconnections.org/ ... n-decades/) was posted last night regarding SAL and its effects on the recent MDR cooling (-0.4C average). As we thought, this was quite a historic SAL outbreak:

https://i.ibb.co/xz9FD2C/0620-Lowry-Fig1.jpg

Man ….. that is as far out as the excessive May/June African rain anomalies.....

[MarioProtVI]

According to data from ESRL’s NCEP/NCAR SST reanalysis, the AMO in June ‘20 has been cooler than in June ‘17, owing to greater North Atlantic Deep Water (NADW) penetration. This is why slight changes in the synoptic pattern produce significant ± fluctuations in SSTs across the North Atlantic basin, given the presence of very cold subsurface waters in the eastern subtropics and far North Atlantic. I’m still uncertain as to whether cool neutral ENSO and a strong WAM/AEJ will be sufficient to overcome the rather anaemic state of the AMO. The AMO, to me, is the biggest potential negative factor that could hinder the 2020 Atlantic hurricane season, not the SAL. Only one and a half week of ridging over the Northwestern Atlantic has been sufficient to eliminate well-below-average SSTs and build a massive warm pool off New England and the Mid-Atlantic region—a feature that is typical of a -AMO regime. This means that the subsurface over the Northwestern (Northeastern) Atlantic is very warm (cold) and easily reaches the surface as soon as low-level winds slacken (strengthen) and veer (back). I would pay more attention to the subsurface than the surface when gauging the state of the AMO. Even if the MDR/Caribbean have been mostly above average for most of June, the preponderance of cold NADW in the eastern subtropics/far North Atlantic means that as soon as trade winds strengthen, virtually all the warm SSTs vanish, as they have in just the past week. Now SSTs in the MDR/Caribbean are average to below average at best.

2018 had a -AMO-ish look to it near peak and look how that turned out. That was because of a strong WAM which is why we saw a good deal of MDR activity despite the SST pattern. So I don’t think we should solely focus on the AMO as the indicator for later in the season, as 2018 taught us.

[CyclonicFury]

According to data from ESRL’s NCEP/NCAR SST reanalysis, the AMO in June ‘20 has been cooler than in June ‘17, owing to greater North Atlantic Deep Water (NADW) penetration. This is why slight changes in the synoptic pattern produce significant ± fluctuations in SSTs across the North Atlantic basin, given the presence of very cold subsurface waters in the eastern subtropics and far North Atlantic. I’m still uncertain as to whether cool neutral ENSO and a strong WAM/AEJ will be sufficient to overcome the rather anaemic state of the AMO. The AMO, to me, is the biggest potential negative factor that could hinder the 2020 Atlantic hurricane season, not the SAL. Only one and a half week of ridging over the Northwestern Atlantic has been sufficient to eliminate well-below-average SSTs and build a massive warm pool off New England and the Mid-Atlantic region—a feature that is typical of a -AMO regime. This means that the subsurface over the Northwestern (Northeastern) Atlantic is very warm (cold) and easily reaches the surface as soon as low-level winds slacken (strengthen) and veer (back). I would pay more attention to the subsurface than the surface when gauging the state of the AMO. Even if the MDR/Caribbean have been mostly above average for most of June, the preponderance of cold NADW in the eastern subtropics/far North Atlantic means that as soon as trade winds strengthen, virtually all the warm SSTs vanish, as they have in just the past week. Now SSTs in the MDR/Caribbean are average to below average at best.

The MDR is still warmer than normal on most datasets, CDAS seems to have a cold bias during/after SAL outbreaks. It is warmer than 2018/19, seasons that managed above normal activity.

[ScottNAtlanta]

Some things to look at...notice the water off southern Brazil. That cold anomaly that showed up in the spring is gone. That is a favorable signal of a positive AMM . The cool GOG in the eastern equatorial Atlantic promotes more precipitation in the Western African Sahel, thus enhances the Western African Monsoon. Bigger wave train. The dust we have seen is a product of the stronger waves we are seeing.

[cycloneye]

 https://twitter.com/webberweather/status/1278070092136427523

[aspen]

https://twitter.com/webberweather/status/1278070092136427523

How do +/-IODs impact Atlantic hurricane season activity? In this situation, would a +IOD help or hamper MDR activity?

[Ubuntwo]

https://twitter.com/webberweather/status/1278070092136427523

How do +/-IODs impact Atlantic hurricane season activity? In this situation, would a +IOD help or hamper MDR activity?

I think the direct influence on the Atlantic hurricane season is poorly studied. However, with increased rainfall over East Africa and reduced SSTs over the far western Pacific, a +IOD would be tangentially tied to increased activity. Nothing major though.

[USTropics]

https://twitter.com/webberweather/status/1278070092136427523

How do +/-IODs impact Atlantic hurricane season activity? In this situation, would a +IOD help or hamper MDR activity?

There is some debate over the connection between IOD and ENSO, but essentially the +/- mode of the IOD can hinder or propel atmospheric changes during ENSO transitions. For instance, a + IOD increases Pacific trade winds, promotes La Nina, and strengthens the Walker circulation. A - IOD creates weaker trade winds, promotes El Nino, and weakens the Walker circulation. So basically the chain is:

positive IOD --> cooling ENSO (La Nina) --> enhanced Walker circulation --> more active Atlantic
negative IOD --> warming ENSO (El Nino) --> weakened Walker circulation --> less active Atlantic

[CyclonicFury]

https://twitter.com/webberweather/status/1278070092136427523

How do +/-IODs impact Atlantic hurricane season activity? In this situation, would a +IOD help or hamper MDR activity?

There is some debate over the connection between IOD and ENSO, but essentially the +/- mode of the IOD can hinder or propel atmospheric changes during ENSO transitions. For instance, a + IOD increases Pacific trade winds, promotes La Nina, and strengthens the Walker circulation. A - IOD creates weaker trade winds, promotes El Nino, and weakens the Walker circulation. So basically the chain is:

positive IOD --> cooling ENSO (La Nina) --> enhanced Walker circulation --> more active Atlantic
negative IOD --> warming ENSO (El Nino) --> weakened Walker circulation --> less active Atlantic

I thought it was the other way around, doesn't a -IOD favor upward motion over the Maritime Continent, which is more La Niña like, while a +IOD favors sinking over this region?

[cycloneye]

How do +/-IODs impact Atlantic hurricane season activity? In this situation, would a +IOD help or hamper MDR activity?

There is some debate over the connection between IOD and ENSO, but essentially the +/- mode of the IOD can hinder or propel atmospheric changes during ENSO transitions. For instance, a + IOD increases Pacific trade winds, promotes La Nina, and strengthens the Walker circulation. A - IOD creates weaker trade winds, promotes El Nino, and weakens the Walker circulation. So basically the chain is:

positive IOD --> cooling ENSO (La Nina) --> enhanced Walker circulation --> more active Atlantic
negative IOD --> warming ENSO (El Nino) --> weakened Walker circulation --> less active Atlantic

I thought it was the other way around, doesn't a -IOD favor upward motion over the Maritime Continent, which is more La Niña like, while a +IOD favors sinking over this region?

Well,no consensus here.

[cycloneye]

Some clarity.

 https://twitter.com/webberweather/status/1278082384102031361