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

[chaser1]

September and October really are behaving like 2007 save for the MDR being more favorable.

Gulf: Two Cat 1 hurricanes and a depression in the in 2007, one storm and one Cat 1 in 2021.
Caribbean: 2007 had Cat 5 Felix early in the month and then literally nothing until October 27. This year has gone without a storm in the Caribbean since late August.
Subtropics: Two short lived subtropical storms in 2007 with both transitioning; 2021 similarly only two short-lived subtropical storms, with neither transitioning fully.
MDR: 2007 saw 3/1/0. This was the biggest difference in performance, with 2021 producing 5/2/2.

https://twitter.com/AndyHazelton/status/1449731427583631366

After reading Andy Hazelton's reference to 2007 being the closest analogue to this year, I was curious about what other large scale variables seemed to be at play and were similarly occurring at this time. Both 2007 and 2021 similarly exhibiting a late season transition to La Nina, however I found the following particularly interesting:

"At the beginning of 2007, the Outgoing Longwave Radiation (OLR) Index was strongly negative, which reflected the enhanced tropical convection and cloudiness across the equatorial Pacific. However, this changed significantly in June when the OLR Index increased to a monthly value of +0.6. Subsequently, the OLR Index has been positive, and the index increased to +1.4 in October, which was the highest value of the year. The most recent monthly averaged OLR Index was again positive, but with a slightly lower value of +0.8 in November. The OLR Index increased significantly in December to a positive monthly value of +2.2, and similar to the SOI this was the highest value of the 2007/2008 La Niña." (this from the National Centers for Environmental Information El Nino Southern Oscillation annual report Nov, 2007 - https://www.ncdc.noaa.gov/sotc/enso/200713 ).

The current (10/16) forecast for MJO related anomalies using GEFS operational forecast for 6-15 day indicates a negative flip in the OLR index primarily for the E. Pacific initially, but with significantly more favorable conditions in the E. PAC as well as the E. GOM and Central & East Caribbean toward the second half of that 6-15 day cycle. Perhaps that time frame better coincides with the eventual passing of the anticipated Kelvin Wave around end of Oct.? In years past where the MJO seemed to play a significant factor, we'd typically await for the EPAC to light up for about a week and then waited for it's transition to then propagate eastward into the Caribbean. Remains to be seen if this late season forecast blip will actually pan out.

Some noteworthy comparisons of 2021 and that year shows 2007 ended with a fairly active 15/6/2 season but and primarily exhibited a lot of "slop" storms. Still, 2007 did product a pair of Cat 5 storms (Dean and Felix) which went on to torch Central America and Yucatan. Interestingly enough and in spite of the very high OLR, a late season hurricane did form (Oct 28 - Nov. 2) just east of PR tracking into the north/central Caribbean impacting DR and central Cuba. Oddly one other short lived TS in December (12/11 - 12/13) also formed east of PR and tracked westward to impact PR & Hispaniola (contrary to more typical Climo development in the W. Carib).

[AlphaToOmega]

For October and November 2021 not to feature a major hurricane, we would likely have to have a Strong La Nina (>1.5 C). Since the start of the satellite era, the only +AMO years with -ENSO that did not feature major hurricanes in either October or November were Strong La Ninas (exempli gratia 2007 and 2010).

[chaser1]

Here is the 1991-2020 climatology

Number Named systems Hurricanes Major Hurricanes
1 Jun 20 Aug 11 Sep 1
2 Jul 17 Aug 26 Sep 19
3 Aug 3 Sep 7 Oct 28
4 Aug 15 Sep 16 -
5 Aug 22 Sep 28 -
6 Aug 29 Oct 15 -
7 Sep 3 Nov 15 -
8 Sep 9 - -
9 Sep 16 - -
10 Sep 22 - -
11 Oct 2 - -
12 Oct 11 - -
13 Oct 25 - -
14 Nov 19 - -

I'm not sure i'm following this correctly? You sure this represents the entirety of the 29 year period shown?

[zhukm29]

Quite some timing for a suppressive Kelvin wave to come in when the MJO arrives for probably the last time during the favorable part of the season, especially during a MJO dependent season. If you had told me 0 storms would form in October during the last week in September, I wouldn't believe it - but now it is actually looking more and more plausible (although I still think we will get at least one during the final week). Good news for the Caribbean though, especially after 2020.

2007 only had one more NS before November 30 (technically two to end the year, but Olga was a rare December storm that isn't guaranteed to happen), so what a tease it would be if we missed the auxiliary list

[AlphaToOmega]

Ah yes, a VERY suppressed look for the Atlantic

[Category5Kaiju]

Ah yes, a VERY suppressed look for the Atlantic

https://i.postimg.cc/V6HkQBNs/cfs-avg-chi200-Mean-global-2.png

We'll see if that verifies or not, but if it does and still nothing forms in the Atlantic even in the last week or few days of October, then at that point I think it can be safely assumed that the MJO propagation may not be entirely to blame for the inactivity in the Atlantic and that there's something else more bizarre going on.

[SFLcane]

Funny how the Atlantic started behaving the opposite of a Nina year as soon as the Nina officially developed. Is there a La Niña version of a Modoki El Niño, where the Nina results in unfavorable conditions across the Atlantic?

This response isn't really because of La Nina. Just a combo of unfavorable MJO plus overall convective response. It's not a La Nina thing

[SFLcane]

Ah yes, a VERY suppressed look for the Atlantic

https://i.postimg.cc/V6HkQBNs/cfs-avg-chi200-Mean-global-2.png

Looks more favorable. We'll see if anything can consolidate

[WiscoWx02]

 https://twitter.com/AndyHazelton/status/1449731427583631366




2007 seems to be coming up a lot, we still had cat 1 hurricane Noel that year though at the end of October. Just something to remember.

[Hammy]

CFS continues to show nothing discernable, though hinting at an EPAC system making it into the Gulf later in the month.

[Category5Kaiju]

Just a question out of curiosty, but were there any times (like in the years since CFS or Tropical Tidbit model-watching really became a commonly performed thing among hurricane trackers) where the models collectively thought that development of some storm or hurricane would occur on the EPAC side, only for them to be completely wrong with development on the Atlantic side, or for the models to flat out miss the genesis of some Atlantic storm that went on to become a decent strength system (like not a pop up, weak TS)?

[AlphaToOmega]

The CFSv2 shows zonal wind anomalies of -4 to -6 knots in the Caribbean. Last year, -4 to -10 knot anomalies for zonal wind were observed in the Caribbean. This year is also forecast to have lower zonal wind anomalies than last year. The CFSv2 shows favorable shear and VP patterns, which is expected in a -ENSO year. The lack of activity is very likely a result of an unfavorable MJO phase and not because of an unfavorable base state. Something similar happened this August; as the MJO was transitioning from Phase VIII to Phase I, the models had difficulty foreseeing activity, which is why storms such as Grace formed with very little model support.

[wxman57]

Here is the 1991-2020 climatology

Number Named systems Hurricanes Major Hurricanes
1 Jun 20 Aug 11 Sep 1
2 Jul 17 Aug 26 Sep 19
3 Aug 3 Sep 7 Oct 28
4 Aug 15 Sep 16 -
5 Aug 22 Sep 28 -
6 Aug 29 Oct 15 -
7 Sep 3 Nov 15 -
8 Sep 9 - -
9 Sep 16 - -
10 Sep 22 - -
11 Oct 2 - -
12 Oct 11 - -
13 Oct 25 - -
14 Nov 19 - -

I'm not sure i'm following this correctly? You sure this represents the entirety of the 29 year period shown?

That's a 30-yr period, by the way. The average number of NS/H/MH is 14/7/3. You can see the full data here: https://www.nhc.noaa.gov/climo/

It's supposed to represent the average date that each NS, H, and MH forms. What caught my eye was the average date of the 3rd MH forming is Oct 28. I cannot find a single case of the 3rd MH forming past about the 3rd week of October, much less an average of the 28th. A number of seasons had less than 3 major hurricanes. I suppose that skewed the results later? Dates for NS and H formation look good. Average first hurricane forming Aug 11 looks good. In fact, the trend is later since 1950, when the average date was earlier in August. Hurricanes are trending later and named storms are earlier, most likely due to better detection of weak storms far out to sea, naming of subtropical storms, and changing naming criteria (trending more liberal).

[Hammy]

Just a question out of curiosty, but were there any times (like in the years since CFS or Tropical Tidbit model-watching really became a commonly performed thing among hurricane trackers) where the models collectively thought that development of some storm or hurricane would occur on the EPAC side, only for them to be completely wrong with development on the Atlantic side, or for the models to flat out miss the genesis of some Atlantic storm that went on to become a decent strength system (like not a pop up, weak TS)?

The GFS and Euro have done this frequently, but the GFS has just as often shown things that aren't there. The Canadian however doesn't have a history of doing this--the instances where the GFS/Euro missed storms still had the Canadian and CFS showing some kind of development.

[aspen]

*pokes the Atlantic* C’mon, do something

*pokes worldwide tropics* C’mon, do something normal

[AlphaToOmega]

It is probably only a matter of time before development is showed on the models. As they say, models show nothing until they show something. There is a forecasted favorable upper-level pattern for the Caribbean.

[Category5Kaiju]

*pokes the Atlantic* C’mon, do something

*pokes worldwide tropics* C’mon, do something normal

The Atlantic right now after being told to produce at least one NS by October's end:

[SFLcane]

It is probably only a matter of time before development is showed on the models. As they say, models show nothing until they show something. There is a forecasted favorable upper-level pattern for the Caribbean.

https://i.postimg.cc/V6HkQBNs/cfs-avg-chi200-Mean-global-2.png
https://i.postimg.cc/pTSz3JHR/cfs-avg-u200a-Mean-global-1.png
https://i.postimg.cc/FRz0PnwT/cfs-avg-u200a-Mean-global-2.png

Gulf and Florida definitely done for the year.

[skyline385]

It is probably only a matter of time before development is showed on the models. As they say, models show nothing until they show something. There is a forecasted favorable upper-level pattern for the Caribbean.

Think that's not going to be enough, there is still tons of shear on the models along with plenty of dry air. The cold fronts also keep dropping and there looks to be a major one coming around Oct 30th over the SE coast.

[Hammy]

It is probably only a matter of time before development is showed on the models. As they say, models show nothing until they show something. There is a forecasted favorable upper-level pattern for the Caribbean.

https://i.postimg.cc/V6HkQBNs/cfs-avg-chi200-Mean-global-2.png
https://i.postimg.cc/pTSz3JHR/cfs-avg-u200a-Mean-global-1.png
https://i.postimg.cc/FRz0PnwT/cfs-avg-u200a-Mean-global-2.png

Think that's not going to be enough, there is still tons of shear on the models along with plenty of dry air. The cold fronts also keep dropping and there looks to be a major one coming around Oct 30th over the SE coast.

Never trust the long range models regarding fronts, the GFS always overplays them.