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

[ElectricStorm]

If none of the three AOIs currently develop, the unfavorable MJO phase will likely halt development for weeks, and September will have had just 3 NS — lower than every other season of the current active stretch. Sept 2021 would be the weakest since 2016 despite Larry; 2017 had multiple long-trackers while 2018, 2019, and 2020 had other significant storms like Helene, Leslie, Humberto, Jerry, Lorenzo, Paulette, and Sally before or after their highest ACE long-tracker. Mindy was brief and Nicholas, while a hurricane landfall, is a far cry from the other storms I mentioned in both intensity and duration.

If no additional storms form, this would raise several questions: what killed September’s momentum despite climo peak coinciding with a developing Nina and an under-performing Pacific? Could we see a double-peak season like 2016 where both peaks are well before/after the normal peak in mid-September? And does this signal what the 2022 season could be like?

Probably similar to the other years that had an active August. Many of them had a less active September, but a few of them rebounded in Oct

[hurricanes1234]

It seems as though this year is one of those years where intraseasonal variation is a huge factor influencing storms.

I remember reading online that intraseasonal oscillation has varying influences from year to year, with some years being strongly influenced by it and others not so much. I recall how in July, there was a gigantic suppressed MJO that shut down the entire basin for two or three weeks after Elsa and activity didn't pick back up until August, only when the strong enhanced MJO moved in. Now that the MJO is back in its unfavourable phase this month and an unfavourable Kelvin wave is also present, we're seeing the same pattern as we did in July. The difference, of course, is that now we're in the climatological peak of the season so systems are still forming (or trying to form) but compared to mid/late August they haven't been as quick to strengthen or develop. More invests have been struggling than not (especially in the last seven days or so). The strongest storm of September so far was Larry but Larry was plagued throughout its life with a so-so environment and structural problems.

If this is indeed one of the years where intraseasonal variation is a dominant factor, then one should assume that things will become more favourable in a few weeks when the intraseasonal oscillation returns to being enhanced. I would probably expect another burst or two of systems rapidly forming/intensifying in October when the base state improves (similar to mid/late August) but I think the Cape Verde season will be wrapping up soon. Even so, as we've seen, a storm doesn't have to be a Cape Verde storm to cause destruction. I still think this season will end above-average. Hyperactive is looking less likely but above-average is still extremely likely IMO.

Just my two cents of course.

[Iceresistance]

Remember that an unfavorable MJO phase could help Tropical Cyclone development in the Atlantic since there are less storms to compete with each other with the sinking air in place, 2017 is a good example.

[Teban54]

It seems as though this year is one of those years where intraseasonal variation is a huge factor influencing storms.

I remember reading online that intraseasonal oscillation has varying influences from year to year, with some years being strongly influenced by it and others not so much. I recall how in July, there was a gigantic suppressed MJO that shut down the entire basin for two or three weeks after Elsa and activity didn't pick back up until August, only when the strong enhanced MJO moved in. Now that the MJO is back in its unfavourable phase this month and an unfavourable Kelvin wave is also present, we're seeing the same pattern as we did in July. The difference, of course, is that now we're in the climatological peak of the season so systems are still forming (or trying to form) but compared to mid/late August they haven't been as quick to strengthen or develop. More invests have been struggling than not (especially in the last seven days or so). The strongest storm of September so far was Larry but Larry was plagued throughout its life with a so-so environment and structural problems.

If this is indeed one of the years where intraseasonal variation is a dominant factor, then one should assume that things will become more favourable in a few weeks when the intraseasonal oscillation returns to being enhanced. I would probably expect another burst or two of systems rapidly forming/intensifying in October when the base state improves (similar to mid/late August) but I think the Cape Verde season will be wrapping up soon. Even so, as we've seen, a storm doesn't have to be a Cape Verde storm to cause destruction. I still think this season will end above-average. Hyperactive is looking less likely but above-average is still extremely likely IMO.

Just my two cents of course.

I think this is the answer. I remember in July people expecting the name Fred to at least be used for a weak TS or something, when in reality it waited until August 11 when intraseasonal signals finally returned (Elsa formed on July 1). Then August went bonkers.

I'm expecting something similar to happen in late September or early October. While it would likely be too late for ACE unless a storm pulls a Cuba 1932, it's potentially much worse from a land impact perspective.

[Category5Kaiju]

It was noted by someone, a tweet maybe, that the jet stream was anomalously far north. I wonder if this actually sets up poorer conditions than expected, even though nina is present. The exciting thing is that we only learn when the unexpected happens, so like a 2013, now we might know what else to look for. Or not.

Whatever the case, we still got a 150 mph Gulf CONUS landfall and did get a major MDR hurricane. We are also almost on the 15th NS; not to mention the basin now has a pretty potent +AMO look and we're headed toward a moderate La Nina, so...idk. If this is true then I think it'd be a first. A lackluster Atlantic, EPAC, and WPAC in September is not something you see often.

[aspen]

It seems as though this year is one of those years where intraseasonal variation is a huge factor influencing storms.

I remember reading online that intraseasonal oscillation has varying influences from year to year, with some years being strongly influenced by it and others not so much. I recall how in July, there was a gigantic suppressed MJO that shut down the entire basin for two or three weeks after Elsa and activity didn't pick back up until August, only when the strong enhanced MJO moved in. Now that the MJO is back in its unfavourable phase this month and an unfavourable Kelvin wave is also present, we're seeing the same pattern as we did in July. The difference, of course, is that now we're in the climatological peak of the season so systems are still forming (or trying to form) but compared to mid/late August they haven't been as quick to strengthen or develop. More invests have been struggling than not (especially in the last seven days or so). The strongest storm of September so far was Larry but Larry was plagued throughout its life with a so-so environment and structural problems.

If this is indeed one of the years where intraseasonal variation is a dominant factor, then one should assume that things will become more favourable in a few weeks when the intraseasonal oscillation returns to being enhanced. I would probably expect another burst or two of systems rapidly forming/intensifying in October when the base state improves (similar to mid/late August) but I think the Cape Verde season will be wrapping up soon. Even so, as we've seen, a storm doesn't have to be a Cape Verde storm to cause destruction. I still think this season will end above-average. Hyperactive is looking less likely but above-average is still extremely likely IMO.

Just my two cents of course.

That answers leads into another question: why are some years more influenced by intraseasonal variation than others? Does it correlate with different ENSO types? Or are they more background processes we still don’t fully understand yet?

If 2021 is and continues to be dictated by intraseasonal oscillations, then the strong -VP surge in the October 10-20th range could yield another spike in activity, like the return to a favorable MJO did in the second half of August.

[tolakram]

It was noted by someone, a tweet maybe, that the jet stream was anomalously far north. I wonder if this actually sets up poorer conditions than expected, even though nina is present. The exciting thing is that we only learn when the unexpected happens, so like a 2013, now we might know what else to look for. Or not.

Whatever the case, we still got a 150 mph Gulf CONUS landfall and did get a major MDR hurricane. We are also almost on the 15th NS; not to mention the basin now has a pretty potent +AMO look and we're headed toward a moderate La Nina, so...idk. If this is true then I think it'd be a first. A lackluster Atlantic, EPAC, and WPAC in September is not something you see often.

Not sure what you are trying to say here. It's not some kind of a contest, instead we try to learn each year what indicators are we seeing or missing, and how are things playing out. Nothing is going to take away number of named storms or the 3 major hurricanes we've had, and if October is extremely above normal then perhaps the Active August / tame September has merit.

[Category5Kaiju]

Not saying it will, but if this season does underperform in the end, then I honestly think it should be a topic of immense discussion and re-analysis by scientists. If it were to do so, then I honestly would be very surprised, perhaps even more surprised than 2013 arguably. The Atlantic Nino, +AMO, Ninos 1-4 regions being cooler than average and solidly trending towards La Nina (possibly a moderate one as well), an active WAM, and a warmer than average MDR (as of recently) are all factors that I think are very indicative of an active season in the end. I also would have to think that these factors would overwhelm any negative factors, many of which are typically not looked at by pros and forecasters as a whole due to how short-lived any of their effects may be when in the context of the season as a whole. I mean, we have not had record breaking SAL outbreaks this year unlike 2020, and from my understanding (I hope at least) the THC did not collapse like it did in 2013. And most importantly, why would the jet stream being more north be bad for hurricanes? Is this the first year something like that happened, or were there other notable years that featured such?

[Category5Kaiju]

It was noted by someone, a tweet maybe, that the jet stream was anomalously far north. I wonder if this actually sets up poorer conditions than expected, even though nina is present. The exciting thing is that we only learn when the unexpected happens, so like a 2013, now we might know what else to look for. Or not.

Whatever the case, we still got a 150 mph Gulf CONUS landfall and did get a major MDR hurricane. We are also almost on the 15th NS; not to mention the basin now has a pretty potent +AMO look and we're headed toward a moderate La Nina, so...idk. If this is true then I think it'd be a first. A lackluster Atlantic, EPAC, and WPAC in September is not something you see often.

Not sure what you are trying to say here. It's not some kind of a contest, instead we try to learn each year what indicators are we seeing or missing, and how are things playing out. Nothing is going to take away number of named storms or the 3 major hurricanes we've had, and if October is extremely above normal then perhaps the Active August / tame September has merit.

Oh yeah I know, I'm not trying to undermine your point. My point is that whatever "ingredients" we are missing still could not prevent the fact that we still had major land impacts, not to mention major hurricanes. Otober is going to be a fun month to watch...

[Hurricaneman]

We’re in a lull right now but as we wind up the month things may get more interesting and especially after the first 5 days of October as the CCKW and MJO become favorable

[tolakram]

Not saying it will, but if this season does underperform in the end, then I honestly think it should be a topic of immense discussion and re-analysis by scientists. If it were to do so, then I honestly would be very surprised, perhaps even more surprised than 2013 arguably. The Atlantic Nino, +AMO, Ninos 1-4 regions being cooler than average and solidly trending towards La Nina (possibly a moderate one as well), an active WAM, and a warmer than average MDR (as of recently) are all factors that I think are very indicative of an active season in the end. I also would have to think that these factors would overwhelm any negative factors, many of which are typically not looked at by pros and forecasters as a whole due to how short-lived any of their effects may be when in the context of the season as a whole. I mean, we have not had record breaking SAL outbreaks this year unlike 2020, and from my understanding (I hope at least) the THC did not collapse like it did in 2013. And most importantly, why would the jet stream being more north be bad for hurricanes? Is this the first year something like that happened, or were there other notable years that featured such?

Every year is "should be a topic of immense discussion and re-analysis by scientists". I think every year we know a little more than the last, unless it goes exactly as expected.

[SouthFLTropics]

I think something can be said for the seasons getting later and later each year. It used to be unlikely to get a named storm in November and practically unheard of to get one in December. Now it seems to be more of a regular occurrence. I'd venture a guess that the seasons are running about 3 to 4 weeks later than they used to. If that is in fact the case, I would expect early to mid October to be fairly active.

[Ubuntwo]

That answers leads into another question: why are some years more influenced by intraseasonal variation than others? Does it correlate with different ENSO types? Or are they more background processes we still don’t fully understand yet?

If 2021 is and continues to be dictated by intraseasonal oscillations, then the strong -VP surge in the October 10-20th range could yield another spike in activity, like the return to a favorable MJO did in the second half of August.

TC activity correlates EXTREMELY well with -VP. Kelvin waves and the MJO modify VP, so they basically steer the patterns of TC formation. Hovmollers like this illustrate it very well:


2021 is a little different from most hurricane seasons in its MJO timing. There is usually an MJO passage around early September, shaping the sharp climo "peak". That peak season surge came about a month early, leading to the crazy August activity we saw.

The shift in timing places unfavorable velocities in September. Which does not mean some magic force pulling the curtain on another 2013. It's just weird timing.

It also doesn't mean a total shutdown of September, depending on CCKW passage (Mindy and Nicholas correspond to a weak Kelvin wave).

The MJO will enter our basin again in mid October, bringing with it a similar spike in TC activity. This will probably be concentrated in the western Caribbean or the Gulf (October climo).

[AlphaToOmega]

If you have any doubts that the rest of September will be active:

-Hurricane Larry, Tropical Storm Mindy, and Hurricane Nicholas formed despite an unfavorable MJO phase
-The ECMWF shows an African Standing Wave for the rest of September (the ECMWF is the most reliable model for intraseasonal variation)
-The ECMWF shows a weak CCKW moving into the basin by late September, allowing for a burst of activity (the ECMWF is the most reliable model for intraseasonal variation)
-There are 3 AoIs in the Atlantic will strong global model and ensemble support despite an unfavorable MJO phase
-The GEFS and ECENS ensembles show a fourth tropical wave emerging off the African coast next week
-Climatology is most favorable in September (climatology is a force that cannot be fought unless there is a really anomalous circumstance)

Unless these change, September will be an active month. I feel like people have so little patience that they write off a month just because AoIs take longer-than-expected to develop.

[CyclonicFury]

If you have any doubts that the rest of September will be active:

-Hurricane Larry, Tropical Storm Mindy, and Hurricane Nicholas formed despite an unfavorable MJO phase
-The ECMWF shows an African Standing Wave for the rest of September (the ECMWF is the most reliable model for intraseasonal variation)
-The ECMWF shows a weak CCKW moving into the basin by late September, allowing for a burst of activity (the ECMWF is the most reliable model for intraseasonal variation)
-There are 3 AoIs in the Atlantic will strong global model and ensemble support despite an unfavorable MJO phase
-The GEFS and ECENS ensembles show a fourth tropical wave emerging off the African coast next week
-Climatology is most favorable in September (climatology is a force that cannot be fought unless there is a really anomalous circumstance)

Unless these change, September will be an active month. I feel like people have so little patience that they write off a month just because AoIs take longer-than-expected to develop.

I think you are clinging too hard to the idea that September was going to be hyperactive. Realistically a 10 named storm September was never likely even if the VP anomaly pattern was ideal. It's not unusual for September to be less active than August in years where August is very active. We've seen 3 storms this month including Larry (3-2-1), but it's possible we don't see another hurricane this month and ACE for the remainder of the month may be lackluster. I wouldn't be surprised if October was more active than normal, though.

[AlphaToOmega]

If you have any doubts that the rest of September will be active:

-Hurricane Larry, Tropical Storm Mindy, and Hurricane Nicholas formed despite an unfavorable MJO phase
-The ECMWF shows an African Standing Wave for the rest of September (the ECMWF is the most reliable model for intraseasonal variation)
-The ECMWF shows a weak CCKW moving into the basin by late September, allowing for a burst of activity (the ECMWF is the most reliable model for intraseasonal variation)
-There are 3 AoIs in the Atlantic will strong global model and ensemble support despite an unfavorable MJO phase
-The GEFS and ECENS ensembles show a fourth tropical wave emerging off the African coast next week
-Climatology is most favorable in September (climatology is a force that cannot be fought unless there is a really anomalous circumstance)

Unless these change, September will be an active month. I feel like people have so little patience that they write off a month just because AoIs take longer-than-expected to develop.

I think you are clinging too hard to the idea that September was going to be hyperactive. Realistically a 10 named storm September was never likely even if the VP anomaly pattern was ideal. It's not unusual for September to be less active than August in years where August is very active. We've seen 3 storms this month including Larry (3-2-1), but it's possible we don't see another hurricane this month and ACE for the remainder of the month may be lackluster. I wouldn't be surprised if October was more active than normal, though.

Each month should be examined individually. An active August does not guarantee an inactive September. What I am seeing from the ECMWF VP charts and ensemble runs shows an active (7+ storms) September. I am also considering climatology, which is most favorable during September. Considering all of these facts, I am still convinced September will be active (7+ storms).

[tolakram]

Each month should be examined individually. An active August does not guarantee an inactive September. What I am seeing from the ECMWF VP charts and ensemble runs shows an active (7+ storms) September. I am also considering climatology, which is most favorable during September. Considering all of these facts, I am still convinced September will be active (7+ storms).

That's a fine opinion to have, but the Euro has not been doing so hot lately. We'll see, need to get to the end and then look back. I think we should question if climatology still applies when we think it should apply, as others have alluded too.

[hurricanes1234]

It seems as though this year is one of those years where intraseasonal variation is a huge factor influencing storms.

I remember reading online that intraseasonal oscillation has varying influences from year to year, with some years being strongly influenced by it and others not so much. I recall how in July, there was a gigantic suppressed MJO that shut down the entire basin for two or three weeks after Elsa and activity didn't pick back up until August, only when the strong enhanced MJO moved in. Now that the MJO is back in its unfavourable phase this month and an unfavourable Kelvin wave is also present, we're seeing the same pattern as we did in July. The difference, of course, is that now we're in the climatological peak of the season so systems are still forming (or trying to form) but compared to mid/late August they haven't been as quick to strengthen or develop. More invests have been struggling than not (especially in the last seven days or so). The strongest storm of September so far was Larry but Larry was plagued throughout its life with a so-so environment and structural problems.

If this is indeed one of the years where intraseasonal variation is a dominant factor, then one should assume that things will become more favourable in a few weeks when the intraseasonal oscillation returns to being enhanced. I would probably expect another burst or two of systems rapidly forming/intensifying in October when the base state improves (similar to mid/late August) but I think the Cape Verde season will be wrapping up soon. Even so, as we've seen, a storm doesn't have to be a Cape Verde storm to cause destruction. I still think this season will end above-average. Hyperactive is looking less likely but above-average is still extremely likely IMO.

Just my two cents of course.

That answers leads into another question: why are some years more influenced by intraseasonal variation than others? Does it correlate with different ENSO types? Or are they more background processes we still don’t fully understand yet?

If 2021 is and continues to be dictated by intraseasonal oscillations, then the strong -VP surge in the October 10-20th range could yield another spike in activity, like the return to a favorable MJO did in the second half of August.

Found this from NOAA. Not sure if the link works (it's a link to a PDF) but they say that MJO activity tends to be strongest in ENSO-neutral years and weakest during moderate to strong El Niño/La Niña years. But they noted that sometimes there might be exceptions (like in late 2007/early 2008 which had solid La Niña conditions but also strong MJO activity).

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/MJO_1page_factsheet.pdf&ved=2ahUKEwi7zbGflITzAhVdRzABHZnqCK4QFnoECAMQBg&usg=AOvVaw2LCB_lRsnz0m2mJr5vSMKl

[AlphaToOmega]

Each month should be examined individually. An active August does not guarantee an inactive September. What I am seeing from the ECMWF VP charts and ensemble runs shows an active (7+ storms) September. I am also considering climatology, which is most favorable during September. Considering all of these facts, I am still convinced September will be active (7+ storms).

That's a fine opinion to have, but the Euro has not been doing so hot lately. We'll see, need to get to the end and then look back. I think we should question if climatology still applies when we think it should apply, as others have alluded too.

From what I have heard, the ECMWF has the best skill for intraseasonal variation.

[ElectricStorm]

If you have any doubts that the rest of September will be active:

-Hurricane Larry, Tropical Storm Mindy, and Hurricane Nicholas formed despite an unfavorable MJO phase
-The ECMWF shows an African Standing Wave for the rest of September (the ECMWF is the most reliable model for intraseasonal variation)
-The ECMWF shows a weak CCKW moving into the basin by late September, allowing for a burst of activity (the ECMWF is the most reliable model for intraseasonal variation)
-There are 3 AoIs in the Atlantic will strong global model and ensemble support despite an unfavorable MJO phase
-The GEFS and ECENS ensembles show a fourth tropical wave emerging off the African coast next week
-Climatology is most favorable in September (climatology is a force that cannot be fought unless there is a really anomalous circumstance)

Unless these change, September will be an active month. I feel like people have so little patience that they write off a month just because AoIs take longer-than-expected to develop.

I think you are clinging too hard to the idea that September was going to be hyperactive. Realistically a 10 named storm September was never likely even if the VP anomaly pattern was ideal. It's not unusual for September to be less active than August in years where August is very active. We've seen 3 storms this month including Larry (3-2-1), but it's possible we don't see another hurricane this month and ACE for the remainder of the month may be lackluster. I wouldn't be surprised if October was more active than normal, though.

Each month should be examined individually. An active August does not guarantee an inactive September. What I am seeing from the ECMWF VP charts and ensemble runs shows an active (7+ storms) September. I am also considering climatology, which is most favorable during September. Considering all of these facts, I am still convinced September will be active (7+ storms).

Nothing I'm seeing right now points to a hyperactive September. -CCKW and an unfavorable MJO phase are about to hit and last for the next few weeks. That doesn't mean nothing will form obviously, but I think a hyperactive 7+ named storm September is highly unlikely at this point. Late August and early September was the active phase this year, now late September is is the less favorable phase, which means October will likely be a favorable phase again. My guess is that the rest of September will not have a whole lot, followed by a dangerous burst of activity sometime in October.