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

[AlphaToOmega]

Not expecting much till mid August at earliest.

https://twitter.com/webberweather/status/1417603827574915078

That would not prevent a Cape Verde or subtropical storm from forming in early August. However, it would keep Central America safe for a little bit.

[SFLcane]

EPAC cell will impart shear til it weakens around aug 10-15. It’s expected

[AlphaToOmega]

EPAC cell will impart shear til it weakens around aug 10-15. It’s expected

Based on the ECMWF, the EPAC cell will last until the end of July. What model are you using?

https://www.ecmwf.int/en/forecasts/charts/catalogue/mofc_multi_mjo_family_time_longitudes?facets=Component,Atmosphere&time=2021071900,0,2021071900&parameter=velocity%20potential%20200%20hPa&filter=no

[Category5Kaiju]

 https://twitter.com/weatherboy789/status/1417636614700998656




While I am not trying to point out anybody in particular, I especially love these kinds of comments; I almost find them to be somewhat enjoyable and entertaining during lulls like these, particularly in a month that isn't supposed to be bustling with activity even in some of the more active years in the past.

[AlphaToOmega]

A lull of activity is not a bellwether for activity later on in the season. Every season, even the hyperactive seasons, have lulls of activity in which there is little to no tropical activity. These lulls are caused by intraseasonal variation.

The Madden-Julian Oscillation is a wave that runs across the equator multiple times a year. The Madden-Julian Oscillation has active and suppressed phases. Throughout the course of a hurricane season, a basin will experience multiple active and suppressed phases. During an active phase, there is rising air over a basin, leading to lower wind shear and higher SSTs. During a suppressed phase, there is sinking air over a basin, leading to higher wind shear and lower SSTs. The MJO always does it course, no matter if a season is hyperactive or inactive.

2005 had a lull of activity in early August; to have thought that such a lull would have meant an inactive season would have been dangerous, for over three thousand people died during that season. 2010 had a lull of activity in late July; however, the season was one of the most active of all time in terms of storms and hurricanes. 2017 had a lull of activity in late July, yet the season had Hurricanes Harvey, Irma, Maria, and Nate. 2020 had a lull of activity in early August, and everyone on this forum knows how active that season was. At the moment, there is a lull of activity in the Atlantic, but that in no way means those in hurricane-prone areas should be laughing too hard.

Hopefully, this post will end the "season cancelled" posts once and for all.

[toad strangler]

A lull of activity is not a bellwether for activity later on in the season. Every season, even the hyperactive seasons, have lulls of activity in which there is little to no tropical activity. These lulls are caused by intraseasonal variation.

The Madden-Julian Oscillation is a wave that runs across the equator multiple times a year. The Madden-Julian Oscillation has active and suppressed phases. Throughout the course of a hurricane season, a basin will experience multiple active and suppressed phases. During an active phase, there is rising air over a basin, leading to lower wind shear and higher SSTs. During a suppressed phase, there is sinking air over a basin, leading to higher wind shear and lower SSTs. The MJO always does it course, no matter if a season is hyperactive or inactive.

2005 had a lull of activity in early August; to have thought that such a lull would have meant an inactive season would have been dangerous, for over three thousand people died during that season. 2010 had a lull of activity in late July; however, the season was one of the most active of all time in terms of storms and hurricanes. 2017 had a lull of activity in late July, yet the season had Hurricanes Harvey, Irma, Maria, and Nate. 2020 had a lull of activity in early August, and everyone on this forum knows how active that season was. At the moment, there is a lull of activity in the Atlantic, but that in no way means those in hurricane-prone areas should be laughing too hard.

Hopefully, this post will end the "season cancelled" posts once and for all.

Who canceled the season?

[SFLcane]

Guys, the shear is totally MJO driven. It's a strong pulse which is why we had way lower shear than usual that allowed Elsa. Now we're getting the flip side. It won't stick around all season because it's driven by that MJO wave which is slower and stronger than originally predicted.

[Category5Kaiju]

A lull of activity is not a bellwether for activity later on in the season. Every season, even the hyperactive seasons, have lulls of activity in which there is little to no tropical activity. These lulls are caused by intraseasonal variation.

The Madden-Julian Oscillation is a wave that runs across the equator multiple times a year. The Madden-Julian Oscillation has active and suppressed phases. Throughout the course of a hurricane season, a basin will experience multiple active and suppressed phases. During an active phase, there is rising air over a basin, leading to lower wind shear and higher SSTs. During a suppressed phase, there is sinking air over a basin, leading to higher wind shear and lower SSTs. The MJO always does it course, no matter if a season is hyperactive or inactive.

2005 had a lull of activity in early August; to have thought that such a lull would have meant an inactive season would have been dangerous, for over three thousand people died during that season. 2010 had a lull of activity in late July; however, the season was one of the most active of all time in terms of storms and hurricanes. 2017 had a lull of activity in late July, yet the season had Hurricanes Harvey, Irma, Maria, and Nate. 2020 had a lull of activity in early August, and everyone on this forum knows how active that season was. At the moment, there is a lull of activity in the Atlantic, but that in no way means those in hurricane-prone areas should be laughing too hard.

Hopefully, this post will end the "season cancelled" posts once and for all.

Well said AlphatoOmega. It almost seems like some people simply believe that an active and impactful season must be active all the time with little to no breaks. If that were the case, then why have we never seen a season with 40 named storms? The Atlantic is not the WPAC, the ocean happens to be near the largest hot desert on the planet (of course the Sahara Dust Layer is a thing as a result), which also happens to put monthly checks on how active a particular Atlantic season could get. Not to mention the MJO is also a thing and that it also acts as an accelerator and brake for a given season's progression. In other words, there's a reason why on average the Atlantic is the third busiest basin in the world instead of being first or second busiest.

[toad strangler]

A lull of activity is not a bellwether for activity later on in the season. Every season, even the hyperactive seasons, have lulls of activity in which there is little to no tropical activity. These lulls are caused by intraseasonal variation.

The Madden-Julian Oscillation is a wave that runs across the equator multiple times a year. The Madden-Julian Oscillation has active and suppressed phases. Throughout the course of a hurricane season, a basin will experience multiple active and suppressed phases. During an active phase, there is rising air over a basin, leading to lower wind shear and higher SSTs. During a suppressed phase, there is sinking air over a basin, leading to higher wind shear and lower SSTs. The MJO always does it course, no matter if a season is hyperactive or inactive.

2005 had a lull of activity in early August; to have thought that such a lull would have meant an inactive season would have been dangerous, for over three thousand people died during that season. 2010 had a lull of activity in late July; however, the season was one of the most active of all time in terms of storms and hurricanes. 2017 had a lull of activity in late July, yet the season had Hurricanes Harvey, Irma, Maria, and Nate. 2020 had a lull of activity in early August, and everyone on this forum knows how active that season was. At the moment, there is a lull of activity in the Atlantic, but that in no way means those in hurricane-prone areas should be laughing too hard.

Hopefully, this post will end the "season cancelled" posts once and for all.

Well said AlphatoOmega.

Nobody canceled the season

We are firmly in the grip of a suppressed background state that we all knew was coming. Enjoy!

[aspen]

Guys, the shear is totally MJO driven. It's a strong pulse which is why we had way lower shear than usual that allowed Elsa. Now we're getting the flip side. It won't stick around all season because it's driven by that MJO wave which is slower and stronger than originally predicted.

So the shear is due to the positive MJO pulse also creating rising air over the EPac, and will ablate once the MJO has completely left the Pacific?

[psyclone]

Just mentioning anything that could possibly be a mitigating factor on the season isn't a "season cancel" post. we should toss that out there. I have not seen any season cancel type posts this year thus far. But i remain every bit as interested in mitigating factors as aggravating ones. We're in our standard July lull which in recent years seems to be routinely consuming the first half of August as well. We'll see if that's the case this year. Even if it is...we're only a month away from Dr Grey's infamous 8-20 bell ring. So we probably have 2 weeks to perhaps as many as 4 or 5 before things get going. Any way you slice it, the climo ramp is quickly approaching. Enjoy the downtime.

[Shell Mound]

I cannot help but think 2021 will be 2017 on steroids.

That’s a very bold call. 2017 featured the highest monthly ACE in September on record. Also, August 2004, if I recall correctly, featured one of the highest ACE indices for the month on record. To match or surpass either August 2004 or September 2017 (or both), 2021 would need to generate numerous long-tracking major hurricanes during either or both of those months, as opposed to short-lived ones like those of 2020. Having several weak and/or short-lived systems would not count. Therefore, 2021 would need to feature a much warmer MDR than is currently present.

 https://twitter.com/AndyHazelton/status/1417529449885675522



 https://twitter.com/AndyHazelton/status/1417532540345278465



 https://twitter.com/AndyHazelton/status/1417533978765058048




VWS was apparently well above average during June 2021 and has only recently dipped well below average. On the other hand, I disagree with the notion that SST alone imply that 2021 will not end up being hyperactive. Both 2010 and 2020 featured SST that would have implied a hyperactive MDR during ASO, yet both ended up underperforming ACE-wise relative to SST. On the other hand, SST were cooler during 1996, 1999, and 2003, yet those years ended up with seasonal ACE indices comparable to those of 2010 and 2020. 2005 also featured much less ACE in the MDR than its near-record-breaking SST would have implied. I think VWS, to some extent, and ENSO could prove better indicators of ACE than SST, at least up to a point. So long as SST are at least somewhat above average, then VWS, ENSO, the Atlantic Niño, and the African monsoon can offset the depressive effects of SST.

[AlphaToOmega]

Does anyone have the TNA values for previous seasons (2020, 2019, 2018, 2017, 2016, etc...)?

[AlphaToOmega]

I found the TNA data here, and here is the data for this current +AMO phase.

1995 -0.05 -0.04 -0.05 0.11 0.30 0.48 0.58 0.59 0.40 0.37 0.51 0.47
1996 0.74 0.40 0.22 0.31 0.36 0.18 0.12 -0.03 0.15 0.08 0.03 0.14
1997 0.31 0.34 0.15 0.27 0.43 0.54 0.34 0.16 0.26 0.59 0.58 0.44
1998 0.43 0.77 0.75 0.59 0.59 0.66 0.56 0.67 0.51 0.49 0.43 0.29
1999 -0.10 -0.20 -0.23 -0.13 0.11 0.15 0.17 0.34 0.38 0.25 0.13 0.27
2000 -0.18 -0.10 0.06 -0.01 -0.06 -0.16 0.01 0.15 0.02 0.00 -0.12 -0.19
2001 -0.13 -0.15 0.15 0.05 0.06 0.24 0.30 0.34 0.51 0.48 0.62 0.66
2002 0.78 0.53 0.37 -0.02 -0.19 -0.13 -0.06 -0.05 0.07 0.36 0.22 0.20
2003 0.27 0.00 0.04 0.00 0.06 0.22 0.36 0.59 0.66 0.80 0.48 0.49
2004 0.50 0.51 0.36 0.46 0.17 0.27 0.46 0.68 0.59 0.62 0.63 0.53
2005 0.46 0.38 0.68 0.81 1.01 0.92 0.84 0.74 0.73 0.54 0.40 0.55
2006 0.41 0.19 0.18 0.41 0.43 0.52 0.36 0.53 0.69 0.74 0.71 0.47
2007 0.46 0.56 0.33 0.40 0.21 0.16 0.09 0.01 0.11 0.24 0.24 0.09
2008 0.14 0.18 0.27 0.09 0.28 0.39 0.45 0.45 0.57 0.43 0.27 0.26
2009 0.07 -0.37 -0.34 -0.31 -0.23 0.05 0.45 0.41 0.35 0.63 0.51 0.54
2010 0.80 1.07 1.27 1.40 1.35 1.11 1.01 0.97 0.75 0.77 0.70 0.96
2011 0.97 0.53 0.41 0.33 0.41 0.59 0.43 0.49 0.36 0.44 0.21 0.23
2012 0.16 -0.02 -0.26 -0.17 0.09 0.31 0.30 0.52 0.72 0.78 0.75 0.55
2013 0.44 0.40 0.70 0.53 0.64 0.32 0.34 0.56 0.61 0.66 0.32 0.27
2014 0.13 -0.08 -0.35 -0.21 -0.06 -0.05 0.14 0.23 0.51 0.56 0.35 0.34
2015 0.17 0.11 -0.11 -0.24 0.08 -0.07 0.16 0.43 0.72 0.93 0.49 0.42
2016 0.50 0.45 0.39 0.32 0.38 0.39 0.37 0.49 0.39 0.55 0.46 0.52
2017 0.49 0.23 0.13 0.47 0.58 0.60 0.60 0.67 0.52 0.45 0.53 0.54
2018 0.28 -0.09 0.02 -0.17 -0.40 -0.48 -0.21 0.01 0.33 0.29 -0.01 -0.04
2019 0.08 0.14 0.01 -0.02 0.12 0.30 0.37 0.42 0.57 0.44 0.26 0.25
2020 0.25 0.50 0.73 0.62 0.52 0.72 0.65 0.59 0.52 0.61 0.39 0.46
2021 0.52 0.41 0.14 0.32 0.24 -0.08 -99.99 -99.99 -99.99 -99.99 -99.99 -99.99

An interesting thing to note is that 2000, 2002, 2014, 2015, and 2018 had -TNA during June. However, every season during this +AMO phase had +TNA during September.

[SFLcane]

EPAC cell is still shearing the Caribbean and west Atlantic to pieces in 2 weeks.

[AlphaToOmega]

Below-average shear in the Gulf of Mexico and the subtropics is expected; that would still prevent something from forming in the Caribbean Sea, keeping Central America safe for early August.

[Shell Mound]

I cannot help but think 2021 will be 2017 on steroids.

That’s a very bold call. 2017 featured the highest monthly ACE in September on record. Also, August 2004, if I recall correctly, featured one of the highest ACE indices for the month on record. To match or surpass either August 2004 or September 2017 (or both), 2021 would need to generate numerous long-tracking major hurricanes during either or both of those months, as opposed to short-lived ones like those of 2020. Having several weak and/or short-lived systems would not count. Therefore, 2021 would need to feature a much warmer MDR than is currently present.

https://twitter.com/AndyHazelton/status/1417529449885675522
https://twitter.com/AndyHazelton/status/1417532540345278465
https://twitter.com/AndyHazelton/status/1417533978765058048

VWS was apparently well above average during June 2021 and has only recently dipped well below average. On the other hand, I disagree with the notion that SST alone imply that 2021 will not end up being hyperactive. Both 2010 and 2020 featured SST that would have implied a hyperactive MDR during ASO, yet both ended up underperforming ACE-wise relative to SST. On the other hand, SST were cooler during 1996, 1999, and 2003, yet those years ended up with seasonal ACE indices comparable to those of 2010 and 2020. 2005 also featured much less ACE in the MDR than its near-record-breaking SST would have implied. I think VWS, to some extent, and ENSO could prove better indicators of ACE than SST, at least up to a point. So long as SST are at least somewhat above average, then VWS, ENSO, the Atlantic Niño, and the African monsoon can offset the depressive effects of SST.

Seasonal ACE:

• 1996: 166
• 1999: 177
• 2003: 177
• 2004: 226
• 2010: 165
• 2020: 180

Red = Greater ACE than either 2010 or 2020
Bolded red = Greater ACE than both 2010 and 2020

The above image shows SST anomalies in the tropical Atlantic basin (MDR + Caribbean) during ASO of the aforementioned years vs. ASO of 2010 and 2020. As the data indicate, the years 1996, 1999, 2003, and 2004 featured, on average, cooler SST during ASO than did either 2010 or 2020 during the same months, yet these four seasons ended up with seasonal ACE indices roughly ≥ those of 2010 and 2020. Conversely, given record-breaking warm SST and low VWS during ASO of 2010 and 2020, one would have expected those years to have produced ACE on a par with years such as 1933, 2004, 2005, and/or 2017. Yet in fact the relatively “cooler” years mentioned previously ended up with similar or greater ACE than either 2010 or 2020 (or both). Clearly, then, hyperactivity, at least insofar as ACE is concerned, is based on far more than simply warm SST. If this were not the case, than years such as 1996, 1999, 2003, and/or 2004 should have ended up with lower ACE than either 2010 or 2020 (or both).

[Shell Mound]

SST during June of years with top-five highest ACE indices (since 1995):


SST during June 2021:

[cycloneye]

Two NHC fellows chim in.

 https://twitter.com/AndyHazelton/status/1417813380337909761




 https://twitter.com/pppapin/status/1417819252585795589




 https://twitter.com/EricBlake12/status/1417819759375159297




 https://twitter.com/EricBlake12/status/1417821173610651654

[tolakram]

Shear forecasts are almost always wrong. Not sure why anyone is even looking at them, other than shear boredom.