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

[AlphaToOmega]

Top 5 analogs according to Tropical Tidbits: 2010, 2000, 2013, 2017, and 1996
Things to note:
1. This is using CDAS SST analysis, which has a major cold bias for the MDR
2. This is using deviations from the global mean SST anomaly
3. This is using a one-month average
4. This has 2013 as an analog, which should be discarded unless the AMOC entirely shuts down

[Spacecoast]

I was curious about how well the 2021 forecasts are stacking up..
It seems to me they will (slightly) underestimate activity again this year.

Named Storms:
2021 CSU forecast was eighteen, so far we have had twelve.
Six more?

Hurricanes:
2021 CSU forecast was eight, so far we have had five.
Three more?

Major Hurricanes:
2021 CSU forecast was four, so far we have had three
One more?

Last year (2020) CSU predicted 24 named storms, 12 hurricanes and five major hurricanes.
Observed activity was 30 named storms, 13 hurricanes and six major hurricanes.

PROBABILITIES FOR AT LEAST ONE MAJOR HURRICANE LANDFALL (AFTER 4 AUGUST):
1) Entire continental U.S. coastline - 65% (full-season average: 52%)
2) U.S. East Coast Including Peninsula Florida - 40% (full-season average: 31%)
3) Gulf Coast from the Florida Panhandle westward to Brownsville - 41% (season average: 30%)

PROBABILITY FOR AT LEAST ONE MAJOR TRACKING INTO THE CARIBBEAN (AFTER 4 AUGUST):
1) 54% (full-season average for last century is 42%)

This seems like these probabilities should have been closer to 85%
IDA tracked through the caribbean, and made landfall fall near Port Fourchon, La., so it seems to have covered all these except:
2) U.S. East Coast Including Peninsula Florida.

[AlphaToOmega]

I was curious about how well the 2021 forecasts are stacking up..
It seems to me they will (slightly) underestimate activity again this year.

Named Storms:
2021 CSU forecast was eighteen, so far we have had twelve.
Six more?

Hurricanes:
2021 CSU forecast was eight, so far we have had five.
Three more?

Major Hurricanes:
2021 CSU forecast was four, so far we have had three
One more?

Last year (2020) CSU predicted 24 named storms, 12 hurricanes and five major hurricanes.
Observed activity was 30 named storms, 13 hurricanes and six major hurricanes.

PROBABILITIES FOR AT LEAST ONE MAJOR HURRICANE LANDFALL (AFTER 4 AUGUST):
1) Entire continental U.S. coastline - 65% (full-season average: 52%)
2) U.S. East Coast Including Peninsula Florida - 40% (full-season average: 31%)
3) Gulf Coast from the Florida Panhandle westward to Brownsville - 41% (season average: 30%)

PROBABILITY FOR AT LEAST ONE MAJOR TRACKING INTO THE CARIBBEAN (AFTER 4 AUGUST):
1) 54% (full-season average for last century is 42%)

This seems like these probabilities should have been closer to 85%
IDA tracked through the caribbean, and made landfall fall near Port Fourchon, La., so it seems to have covered all these except:
2) U.S. East Coast Including Peninsula Florida.

NOAA forecasts are typically conservative. In fact, it seems like it is standard practice for meteorologists to be bearish with forecasts.

[Woofde]

Larry is churning out some serious ACE units right now. When it's all added up, Larry should bring our season total to around 75-80. That's roughly equal to the end of September for climatology, and equal to about half the ACE required for a hyperactive season. Considering that we are looking at a likely backloaded season due to the La Nina, it seems likely that 2021 will end up hyperactive.

[AlphaToOmega]

Larry is churning out some serious ACE units right now. When it's all added up, Larry should bring our season total to around 75-80. That's roughly equal to the end of September for climatology, and equal to about half the ACE required for a hyperactive season. Considering that we are looking at a likely backloaded season due to the La Nina, it seems likely that 2021 will end up hyperactive.

Has the threshold for hyperactivity changed to 210 ACE (1991-2020 averages)?

[Teban54]

Larry is churning out some serious ACE units right now. When it's all added up, Larry should bring our season total to around 75-80. That's roughly equal to the end of September for climatology, and equal to about half the ACE required for a hyperactive season. Considering that we are looking at a likely backloaded season due to the La Nina, it seems likely that 2021 will end up hyperactive.

Has the threshold for hyperactivity changed to 210 ACE (1991-2020 averages)?

No:

The phrase "total overall seasonal activity" refers to the combined intensity and duration of Atlantic named storms and hurricanes occurring during the season. The measure of total seasonal activity used by NOAA is the Accumulated Cyclone Energy. The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named storms while they are at least tropical storm intensity. The 1991-2020 mean value of the ACE index is 122.1 x 104 kt2, and the median value is 129.5 x 104 kt2. With most of 1991-2020 being in an active era, using ACE values from 1951-2020 is more representative of the possible ranges of activity that can result in similar ACE values. The 1951-2020 ACE median is 96.7 x 104 kt2

The following classifications are based on an approximate tercile partitioning of seasons based on the ACE index, combined with the seasonal number of tropical storms, hurricanes and major hurricanes.

Extremely active season: An ACE index above 159.6 x 104 kt2 (corresponding to 165% of the 1951-2020 median).

Above-normal season: An ACE index above 126.1 x 104 kt2 (corresponding to the 67th percentile of the ACE values from 1951-2020).

Below-normal season:An ACE index below 73.0 x 104 kt2 (corresponding to less than 33rd percentile of the values from 1951-2020 median).

Near-normal season: Neither the above- nor below-normal season criteria are met.
A near-normal season will typically have an ACE range of 73-126 x 104 kt2 (corresponding to approximately 75%-130% of the 1951-2020 median).

[Woofde]

Larry is churning out some serious ACE units right now. When it's all added up, Larry should bring our season total to around 75-80. That's roughly equal to the end of September for climatology, and equal to about half the ACE required for a hyperactive season. Considering that we are looking at a likely backloaded season due to the La Nina, it seems likely that 2021 will end up hyperactive.

Has the threshold for hyperactivity changed to 210 ACE (1991-2020 averages)?

The wording makes it a little hard to tell. I believe they are using the (1951-2020) averages instead, but I may be wrong.

"Hurricane season averages and classifications for overall activity are based on data from the 30-year period 1991-2020. This base period is updated from the prior period, 1981-2010, as is customary with the calculation of normals for many variables. The update to normals is routinely accomplished, every 10 yeras."

"With most of 1991-2020 being in an active era, using ACE values from 1951-2020 is more representative of the possible ranges of activity that can result in similar ACE values. The 1951-2020 ACE median is 96.7 x 104 kt2"

https://www.cpc.ncep.noaa.gov/products/ ... round.html

[Shell Mound]

I think it's also interesting to note that 4 of the 5 hurricanes became hurricanes in the deep tropics south of 20°N. The deep tropics have been quite active thus far, in contrast to what some were anticipating.

Actually, Ida became a hurricane at 21.4°N, and Henri became a hurricane much farther north. So three of the five actually became hurricanes in the deep tropics.

[cycloneye]

 https://twitter.com/MJVentrice/status/1434497835194585092

[AlphaToOmega]

https://twitter.com/MJVentrice/status/1434497835194585092

Climatology cannot be stopped. Look at the September 2019 VP anomaly pattern: it looks unfavorable. Despite that, seven storms developed within September 2019. It would take an extremely powerful force to fight climatology.

[aspen]

Many above-average seasons with a very active August were followed by a quality-over-quantity September, with less storms overall but more big ones and long trackers.

September 2004 had 4 NS compared to a whopping 8 in August, but all four September storms were long-tracking hurricanes. That month also had the most ACE in a single month until being surpassed by September 2017.

September 2012 had only two new storms while August had 8 (Leslie lasted into September), but all were hurricanes. Michael was a major and Nadine just would not die.

1995 only had 3 NS form in September following Luis dissipating, but all three were hurricanes, including the strong Cat 4 Opal.


Also, other active seasons had relatively lackluster Septembers but still ended up as above-average in terms of NS and ACE. 2008 only had 4 NS in September, and Ike was the only one of any significance, but the following months had a Cat 4 each and four additional storms total. September 2016 was nothing but weak struggling TS systems until Matthew blew up in the Caribbean near the very end of the month. September 2000 took some time to get going, but ended up producing 3 Cat 1s and 2 Cat 4s. It is quite possible 2021 ends up with a September break or has less storms than August, but will finish strong.

[AlphaToOmega]

We may or may not have a lull right now, but that does not mean September will be inactive. September 2019 had a lull of activity in early September; seven storms formed that month. I think it is likely that we will see at least seven storms this month given the favorable pattern forecasted by the models. Something would have to really screw up for that to bust

[Category5Kaiju]

Many above-average seasons with a very active August were followed by a quality-over-quantity September, with less storms overall but more big ones and long trackers.

September 2004 had 4 NS compared to a whopping 8 in August, but all four September storms were long-tracking hurricanes. That month also had the most ACE in a single month until being surpassed by September 2017.

September 2012 had only two new storms while August had 8 (Leslie lasted into September), but all were hurricanes. Michael was a major and Nadine just would not die.

1995 only had 3 NS form in September following Luis dissipating, but all three were hurricanes, including the strong Cat 4 Opal.


Also, other active seasons had relatively lackluster Septembers but still ended up as above-average in terms of NS and ACE. 2008 only had 4 NS in September, and Ike was the only one of any significance, but the following months had a Cat 4 each and four additional storms total. September 2016 was nothing but weak struggling TS systems until Matthew blew up in the Caribbean near the very end of the month. September 2000 took some time to get going, but ended up producing 3 Cat 1s and 2 Cat 4s. It is quite possible 2021 ends up with a September break or has less storms than August, but will finish strong.

I personally have a hard time believing September will be as quiet as some are suggesting. Yes, we may have had a very active August and the MJO would naturally enter a suppressive phase 30-40 days later, but is it going to be enough to hinder activity in the Atlantic during peak season, especially with an impending La Nina and what looks to be a sinking cell over the EPAC with models not very enthusiastic on strong development there? I don't think so, that would literally defy climatology.

[SFLcane]

 https://twitter.com/adrianlinares28/status/1434505387017973762

[AlphaToOmega]

Many above-average seasons with a very active August were followed by a quality-over-quantity September, with less storms overall but more big ones and long trackers.

September 2004 had 4 NS compared to a whopping 8 in August, but all four September storms were long-tracking hurricanes. That month also had the most ACE in a single month until being surpassed by September 2017.

September 2012 had only two new storms while August had 8 (Leslie lasted into September), but all were hurricanes. Michael was a major and Nadine just would not die.

1995 only had 3 NS form in September following Luis dissipating, but all three were hurricanes, including the strong Cat 4 Opal.


Also, other active seasons had relatively lackluster Septembers but still ended up as above-average in terms of NS and ACE. 2008 only had 4 NS in September, and Ike was the only one of any significance, but the following months had a Cat 4 each and four additional storms total. September 2016 was nothing but weak struggling TS systems until Matthew blew up in the Caribbean near the very end of the month. September 2000 took some time to get going, but ended up producing 3 Cat 1s and 2 Cat 4s. It is quite possible 2021 ends up with a September break or has less storms than August, but will finish strong.

There were also seasons with a very active August as well as a very active September. 1969 comes to mind as one of these. A lackluster September does not guarantee an inactive season, but a lackluster September seems unlikely as of now. It would take a very strong suppressed MJO phase in September to produce such a scenario.

[LarryWx]

Many above-average seasons with a very active August were followed by a quality-over-quantity September, with less storms overall but more big ones and long trackers.

September 2004 had 4 NS compared to a whopping 8 in August, but all four September storms were long-tracking hurricanes. That month also had the most ACE in a single month until being surpassed by September 2017.

September 2012 had only two new storms while August had 8 (Leslie lasted into September), but all were hurricanes. Michael was a major and Nadine just would not die.

1995 only had 3 NS form in September following Luis dissipating, but all three were hurricanes, including the strong Cat 4 Opal.


Also, other active seasons had relatively lackluster Septembers but still ended up as above-average in terms of NS and ACE. 2008 only had 4 NS in September, and Ike was the only one of any significance, but the following months had a Cat 4 each and four additional storms total. September 2016 was nothing but weak struggling TS systems until Matthew blew up in the Caribbean near the very end of the month. September 2000 took some time to get going, but ended up producing 3 Cat 1s and 2 Cat 4s. It is quite possible 2021 ends up with a September break or has less storms than August, but will finish strong.

I personally have a hard time believing September will be as quiet as some are suggesting. Yes, we may have had a very active August and the MJO would naturally enter a suppressive phase 30-40 days later, but is it going to be enough to hinder activity in the Atlantic during peak season, especially with an impending La Nina and what looks to be a sinking cell over the EPAC with models not very enthusiastic on strong development there? I don't think so, that would literally defy climatology.

There’s no suggestion Sept will turn out quiet. First, Larry is looking to end up being a hurricane for 10+ days and a MH for most of that period. In terms of ACE, that’s strong activity by itself….lots of energy for the first 13+ days of the month! Second, if the EPS has the right idea, there will be only a couple of days between the demise of Larry and the next MDR system or two. Third, there’s the threat of Gulf activity over the next 10 days or so. That may produce 1-2 more TCs. Fourth, ensembles go out only through 9/20-1. That still leaves ~1/3 of the month that can’t even be seen yet. Fifth, there usually are one or more TCs that aren’t even hinted at far in advance on models.

So, there really is no indication of anything less than an active Sept based on objective measurements.

[AutoPenalti]

Hold up, so about a couple post back in the Outlook thread there was heavy signal on the EPS for a TC to form in the MDR, followed by subsequent posts of favorable conditions for the rest of September, now on this thread there’s an unfavorable MJO phase in the latter half of September, but then another post that shows a Kelvin wave that will support favorable genesis.


So which is it? lol.

[LarryWx]

I forgot to add the chance of a far eastern MDR TC, sharp recurve or not, near 9/11-12 from the suggested very strong AEW still forecasted over Africa in a few days and then moving offshore ~9/11.

[Category5Kaiju]

Hold up, so about a couple post back in the Outlook thread there was heavy signal on the EPS for a TC to form in the MDR, followed by subsequent posts of favorable conditions for the rest of September, now on this thread there’s an unfavorable MJO phase in the latter half of September, but then another post that shows a Kelvin wave that will support favorable genesis.


So which is it? lol.

Considering how the Atlantic has been performing quite recently, I am willing to bet all of my hurricane tracking loving spirit that the former will be the case. I clearly do not see the WPAC or EPAC even remotely awake, let alone generating quality storms and being very active anytime soon. This is also definitely not another 2013 as we are already 12/5/3 (and it's only September 5!) If anything, I am willing to bet that by October 1, we will be at least at Rose.

[jconsor]

https://twitter.com/MJVentrice/status/1434497835194585092

This tweet from Dr. Ventrice is strongly misleading IMHO. MJO and Kelvin wave pattern favors an active second half of Sep in the tropical Atlantic.

 https://twitter.com/webberweather/status/1434519996302970882