2016-2017 Southern Hemisphere tropical cyclone season

[Calasanjy]

I am a little surprised that this topic has not already been created in light of the fact that there are already topics for the 2017 Eastern and Western Pacific seasons which have not yet started, but the 2016-2017 tropical cyclone season is well underway in the Southern Hemisphere. Strangely, it has been dead for the last several months, as the only tropical cyclone to have formed this season was 01S/Abela in July of all months in the Southwest Indian Ocean. A few invests spun up in November, but quickly disintegrated.

According to the Colorado State University information provided at the following link, the Accumulated Cyclone Energy for the Southern Hemisphere this season as of today is 2.4, which pales in comparison to the 1981-2010 average of 24.6. As mentioned above, there has been only one JTWC-warned TC this season (01S/Abela in JULY). The average to this point according to the CSU data is 4 JTWC-warned TCs:

http://tropical.atmos.colostate.edu/Realtime/

Most of the drastic departure from the 1981-2010 cyclone season activity can be attributed to lack of activity in the South Indian Ocean (average of 3.1 JTWC-warned TCs to this point in comparison to an average of 0.9 in the South Pacific Ocean). Based on some information I have found, it seems that the monsoon trough may dip further south in a week or so enhancing the potential for cyclone development in the Southern Hemisphere, particularly to the northwest of Australia south of Sumatra, but the season is still well below average to this point.

Any thoughts on the reasons for the inactivity since July in the Southern Hemisphere? Of course there is not usually much activity until October or November, but the entire hemisphere has remained dead tropics-wise during this entire period through today.

[1900hurricane]

99P is now up.

[Calasanjy]

Thanks for the update - I saw that 99P is now active and the JTWC currently has it classified as having a low chance of development. It would be nice to track a cyclone in this region at last as long as it does not have any adverse effects.

I just found it surprising and a little alarming that that the Southern Hemisphere has not produced any JTWC-numbered cyclones since July, as that is a significant departure from normal.

[1900hurricane]

It might be worth noting that the SIO did produce a named subtropical system, Bransby, which was not given any advisories by JTWC (since they don't issue advisories on subtropical systems). Regardless, the SHEM has been tame so far this season.

[euro6208]

[euro6208]

EURO agrees with GFS on a cyclone passing close to Socotra in the Arabian Sea as well as another cyclone meandering west of Fiji in the South Pacific.

Both seems to develop a very strong cyclone Northwest of Australia with EURO bottoming it out at 979 mb and GFS at 934 mb. GFS even takes this to East Timor and Timor and passes it south of Sumba.

Now that would be something.

[euro6208]

Peaks at 908mb and landfalls over Northwest Australia.

[Calasanjy]

It would be startling to see a cyclone of that intensity, but stranger things have happened.

It now appears the area near Fiji (TD04F/Invest 99P) is struggling to develop. There is a possibility that two cyclones could form off northern Australia in the coming week, however. At least one cyclone appears to be well-predicted by the models. Dr. Klotzbach mentioned on Twitter that the 2016-2017 cyclone season currently has the lowest ACE to date on record, which is since 1960.

[Calasanjy]

It might be worth noting that the SIO did produce a named subtropical system, Bransby, which was not given any advisories by JTWC (since they don't issue advisories on subtropical systems). Regardless, the SHEM has been tame so far this season.

I'm not considering subtropical systems in my assessment. However, I am happy to see the Meteo-France jurisdiction crossing another name off its list.

[Calasanjy]

What is going on in the Southern Hemisphere this year? The accumulated cyclone energy (ACE) is 4.8, which is slightly higher than ten percent of the 45 units of expected ACE to this point in the cyclone season (which technically runs from July 1 through June 30, but is typically active from the middle of November through April). The statistics are shown on the Colorado State University tropical meteorology Website:

http://tropical.atmos.colostate.edu/Realtime/

I realize that there are still several months to come in this season, so we could still have a reversal. Of course, I am not wishing for people to be harmed by cyclones, but it would be nice to have some "fish" over the central southern Indian Ocean or the open waters of the South Pacific to track, as we are supposed to have this time of year. As someone who finds Southern Hemisphere cyclones very intriguing, I have been quite bored so far this season.

Any thoughts on causes of the inactivity, or if the SHEM will become more active in coming weeks? There is a strong low over Australia which could move over water and become a weak-to-modest cyclone, although the models I have seen (GFS and NAVGEM) currently have it extremely close to the coast or inland. In addition, there is an area of disturbed weather southwest of Sumatra and another one that some models forecast to form near Madagascar in the next week. It seems that only areas near landmasses have seen much convection the last month or two, in many cases preventing consolidation into tropical cyclones.

It is also worth noting that the 2015-2016 season only had 20 JTWC-warned tropical cyclones, which is a stark contrast to the multiple seasons in the 1980s and 1990s with 30 or more such cyclones. No season since the start of the new millennium has recorded 30 or more JTWC-warned tropical cyclones.

I look forward to hearing thoughts on this.

Thanks,

Calasanjy

[euro6208]

Current season compared to climatology...Very quiet down there.

[euro6208]

[euro6208]

The quietness continues.

EURO doesn't develop anything in the SHEM. GFS however for the past few runs has an Australian Cyclone.

[Calasanjy]

Thanks. Yes, I have not seen much of anything predicted by the majority of the models in the Southern Hemisphere in the coming week. I may now go watch paint dry instead of paying attention to this thus-far-nonexistent cyclone season.

In all seriousness, I plan to do a little more research on the atmospheric conditions impacting the formation of cyclones in the Southern Hemisphere to see if I can identify any definite explanations for this lack of activity (aside from the fact that ocean temperatures in the South Indian Ocean are currently cooler than normal). I am specifically interested in the following:

- Comparison of the number of tropical cyclones in the Southern Hemisphere during globally-warmer versus cooler years

- Correlations in activity between the traditional Southern Hemisphere basins (excluding the South Atlantic) and those in other parts of the world (if any significant correlations)
- I did read of a supposed positive correlation between Southern and Northwest Pacific cyclone activity

- Interactions between El Nino/La Nina and the Pacific Decadal Oscillation, Indian Ocean Dipole, and other multiannual/decadal cycles, as well as their influence upon tropical cyclone formation in each of the Southern Hemisphere basin (again, if any significant correlations exist)
I am aware of the following:
- Definite enhancement of TC activity in the central South Pacific during El Nino years/seasons, and suppression during La Nina years/seasons
- Definite enhancement of TC activity in the waters surrounding Australia during La Nina years/seasons, and suppression during El Nino years/seasons
- A potential suppression of Southwest Indian Ocean TC activity during El Nino and La Nina years/seasons, and enhancement during neutral years/seasons (further research probably needed on this)

If anyone has any thoughts on this (or even better, substantive data regarding any of the items mentioned above), please feel free to share. I have been somewhat dismayed by the lack of data and historical analysis available online on Southern Hemisphere tropical cyclones, although it is certainly much better than what was available in 2000 when I started following Southern Hemisphere tropical cyclones. For instance, many tropical cyclones from the 1980s and before have been reanalyzed based on satellite imagery and found to have been (in some cases significantly) stronger than originally thought. I intend to post on this at some point. On that note, if anyone has ever seen a satellite image of Cyclone Elinah from the quite inactive 1982-1983 Southwest Indian Ocean season, it is obvious to me that it was not a tropical storm as it was originally classified. It looks more like a Category 3 or 4 hurricane from my judgement. Images of this storm as well as others from that era are available on Wikipedia as well as the great (for information on Southwest Indian Ocean tropical cyclones) Website http://www.firinga.com.

[Calasanjy]

Other factors which should be taken into account include the Antarctic Oscillation and Walker circulations, the latter of which is found to inhibit tropical cyclone formation in the Southwest Indian Ocean, such as during the 2010-2011 season, which also occurred during a La Nina episode.

Anyway, some of the models are now picking up on potential formation of a cyclone north of the Mascarene Islands in the coming week.

[Digital-TC-Chaser]

GFS is hinting the last week of Jan will active in the shem the IO and SPAC, shem cyclones are mostly triggered by either a MT or the MJO. One thing to note is the SAM has been mostly in a negative phase so far this season and may be the reason for such the dismal season, ridges have been pushing all the way up to almost the EQ in the SW IO so far. And the occasional strong cold fronts are still moving over the SW IO. NZ has been battered by all season by a procession of CFronts.


http://www.cpc.ncep.noaa.gov/products/p ... .sprd2.gif

[Steve820]

The Southern Hemisphere has been acting really quiet this year. What is going on?! I feel like the Walker circulation could be in place in the SIO this year and, along with cooler than normal SSTs, could be suppressing activity. The SPac is very quiet as we should expect during La Nina, but the Australian region has been very quiet too. Apparently the SHem doesn't get the memo that it is January, and should be getting active. Instead, it's dead quiet... The only in-season named storm (not including off-season storms like Abela and Bransby) in the whole SHem so far was Yvette, which was a weakling. If this inactivity keeps up 2016-17 might go down as the least active SHem season ever recorded. I hope the GFS forecasts noted by Digital-TC-Chaser come true - not that I want destruction, but I want activity for once.

[Calasanjy]

the Australian region has been very quiet too.

As you noted, the only "in-season" tropical cyclone thus far has been the impotent Yvette. Then again, I was not thrilled about the prospect of the 908-mb cyclone that at least one model had forecast at the end of 2016 striking western Australia. I would rather simply have a "normal" season, with many moderate tropical cyclones and a few major storms, hopefully remaining over water. The 2015-2016 season, while quite exactly normal in terms of total ACE, was notable in that the majority of the ACE (if I am correct) was contributed by only two extremely powerful storms (11P/Winston and 19S/Fantala). It was the least active season in terms of JTWC-warned storms since at least the late 1970s, with 20 such storms (there were several prior seasons since the late '70s with 21 JTWC-warned storms). Unless we see a notable burst of activity in the next three months, this season may finish significantly below 20 JTWC-warned storms, beating last season's abnormally-low number.

The major inhibiting factor that I have seen thus far this season for Australian region cyclones has been the landmass of Australia itself. I can think of two lows offhand that would in all likelihood have developed into tropical cyclones had they not moved over Australia (one formed the last week of 2016 simultaneously with Yvette, and the other formed last week). Even though this has been only a weak La Nina episode, the typical pattern of greater concentration of tropical convection around Australia has been evident. I am not sure about the presence of a Walker circulation, although the pattern of activity in the South Indian Ocean seems to match that which would be expected if one were present.

[Digital-TC-Chaser]

[quote="Digital-TC-Chaser"]GFS is hinting the last week of Jan will active in the shem the IO and SPAC, shem cyclones are mostly triggered by either a MT or the MJO. One thing to note is the SAM has been mostly in a negative phase so far this season and may be the reason for such the dismal season, ridges have been pushing all the way up to almost the EQ in the SW IO so far. And the occasional strong cold fronts are still moving over the SW IO. NZ has been battered by all season by a procession of CFronts.

Sam
https://www.youtube.com/watch?v=ZQwgosJ_RL0

STR
http://www.youtube.com/watch?v=mqHbpgzBQLA




Ridge from just below Perth pushing all the way up-to near coco's island blocking MT flow to NW Australia.


Huge cold airmass with a strong front is behind the ridge,for Jan IMO not the typical pattern i would expect to see at
this time of the year. These fronts i think are disrupting the hadley cell that pulls the MT south over EQ.


Interesting there appears to be another wwb across Borneo Indonesia atm,unfortunately on the wrong side of the EQ.

[euro6208]

Both EURO and GFS hinting on a somewhat strong cyclone with the latter almost making a direct hit on Mauritius in the SIO.

They also have a Cyclone threatening Northwest Australia.