2017 indicators: SST's / MSLP / SAL / Steering / Instability

[Steve]

JMA is respected for large scale patterns and sometimes for seasonal deterministic factors. I don't follow it closely because I don't have access to their real products or never found them.

[AutoPenalti]

https://twitter.com/BenNollWeather/status/895600731654299649

Could the ATL get busy by the end of August?


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Hasn't the JMA been almost as bad as the CFS?

JMA is actually really good at forecasting patterns across the region.

Not exactly for hurricanes though.

[dexterlabio]

low RH definitely is not a positive. Probably explains why we do not have anything forming in the GFS

That's kind of puzzling to me because the GFS seems to be putting the active MJO phase over the Western Hemisphere for the next 2 weeks.

Or perhaps there is more for me to learn about MJO/Kelvin wave and the tropics in general, because most of the time I consider it as the be-all, end-all indicator.

[Steve]

It's still early August, and we have high SAL still in a lot of the Eastern Atlantic and even in the MDR. I'm sure that's part of why there is lower relative humidity but since I haven't looked at it historically for similar conditions I don't know if the lower RH is an anomaly.
http://tropic.ssec.wisc.edu/real-time/s ... od=splitEW

Also, here is some of the juice for late August and early September.
http://satellite.imd.gov.in/insat.htm

[cycloneye]

@MJVentrice
When the MJO is located over the Indian Ocean (Blue shading), there's a 4x more likelihood for Hurricanes over the Atlantic Basin

 https://twitter.com/MJVentrice/status/895952133819904000

[Kingarabian]

That chart is confusing. If the MJO being over the Indian ocean favors hurricanes, then why is the Atlantic suppressed in weeks 3 and 4?

Furthermore, the EPS has lower than normal pressures across the Atlantic to end August for a while now -- which in theory would favor TC genesis. However the models continue to be bearish in their respective forecast periods and I expect them to remain that way if the EPac becomes active as the models continue to indicate.

[NDG]

:uarrow: That chart is confusing. If the MJO being over the Indian ocean favors hurricanes, then why is the Atlantic suppressed in weeks 3 and 4?

Furthermore, the EPS has lower than normal pressures across the Atlantic to end August for a while now -- which in theory would favor TC genesis. However the models continue to be bearish in their respective forecast periods and I expect them to remain that way if the EPac becomes active as the models continue to indicate.

An active EPac over the next couple of weeks may affect conditions over the Caribbean but not over the central & eastern Atlantic MDR.

[cycloneye]

@EricBlake12
I'd even argue the first KW occurred in an unfavorable MJO state. The next one has more of a MJO signature, which to me means more impacts

 https://twitter.com/EricBlake12/status/895986597664923649

[cycloneye]

@BenNollWeather
CFSv2 weeklies also indicate that conditions are ripe for an active Africa-Atlantic through at least the first week of September.

 https://twitter.com/BenNollWeather/status/895986356119191553

[tolakram]

Let's look at some familiar graphs and some explanations. I'm learning as I go along here, perhaps a pro met can comment on this.

Source: http://www.ssd.noaa.gov/PS/TROP/TCFP/atlantic.html

Instability


Once again it's flatlined heading into the hear of the season. It's still up to debate if this is a leading or trailing indicator, but it is telling us the MDR has been dead. Note that the normal instability starts to rise faster mid August with a peak in mid October.

Wind Shear


Shear has been decently below average, pressures above average.


SST's above average


IMO, assuming instability is a trailing indicator, it has to be low relative humidity (dry air) that is causing some if not most of the problems right now.

Here's the description (such that it is) of the parameters used on these graphs. I've bolded the ones I'm interested in.

CLIM: Climatological TC formation probability. This was derived from the NHC Atlantic and east Pacific best track files from 1949-2010. Formation was defined as the first entry of tropical depression or higher in the best track. Extratropical cases were excluded.
PLND: The percent of the area covered by an r=500km circle covered by land
DNST: The closest distance to any existing tropical cyclone.
RSST: The average weekly Reynold's SST.
VSHD: The average 850-200 hPa vertical shear.
RVOR: The average 850 hPa relative vorticity.
THDV: The average vertical instability parameter, defined as the vertical average temperature difference between the equivalent potential temperature of a parcel lifted from the surface to 200 hPa, and the saturation equivalent potential temperature of the environment.
HDIV: The average 850 hPa horizontal divergence.
PCCD: The percent of channel 3 pixels colder than -40 degree. All full disk images within 3 hours after and 6 hours before each synoptic time are include, so that this parameter represents the amount of sustained deep convection.
BTWM: The average channel 3 brightness temperature, after the cold pixels in parameter 9 above have been eliminated. This parameter is a measure of mid- to upper-level moisture.
MSLP: The average mean sea level pressure.
TADV: The average 850 hPa horizonal temperature advection.

Looking at those graphs ...

Vorticity looks around average. I assume this can be viewed as a loose measure of waves and other disturbances in the MDR. The more the better.


Cold pixel count looks generally below average, maybe not by much.


BTWM (mid and upper level moisture)


This last graph may be the key? I am assuming this is showing below normal levels of moisture in the mid and upper atmosphere.

Here is more of the product description for how the probability map is created:

In the screening step, the probability of formation is set to zero for 5 by 5 degree areas where formation almost never occurred based upon the best track data (1949-present), NCEP reanalysis fields (1981-present), and GOES climatology (1995-present). The following areas are eliminated:

SCREENING STEP:
Maximum climatological SST < 21 degree C
Latitude < 5 degrees north
Areas that are 100% over land
Areas that already contain a tropical cyclone
850 hPa Circulation < -5 kt
Vertical Shear > 65 kt
Vertical Instability < -8 degrees C
GOES cold pixel count = 0%
GOES brightness temperature > -23 degrees C

Based on the screening steps above we see the limits of even considering an area for development, but some of these are a tad extreme. > 65kt of vertical shear? Seems like that could be lower. The bolded part above is key to understanding the moisture graph. Higher temps = less moisture so the graph is clearly showing the drier air in the MDR. Also note that one of the screening steps is to evaluate instability, throwing out any area less than -8C. Those kinds of readings only occur in the winter so that number is as extreme as the shear number. I'm not sure what that means other than instability may not be that critical of a leading indicator.

Too many graphs, too much text, but hopefully this helps.

[SFLcane]

Ventrice this morning going gang busters on things really popping soon in the Atlantic. Yet no signal in the models...Lets see if this changes soon.

[SFLcane]

CMC up to its craziness with 5 named storms it seems BUT it may not be all the nuts with the potential setting up in the Atlantic this go around.

[Alyono]

CMC up to its craziness with 5 named storms it seems BUT it may not be all the nuts with the potential setting up in the Atlantic this go around.

I only see 2 storms on the CMC run. The low in the Caribbean is not even a TD. The two in the subtropical Atlantic are ET

[Ntxw]

Ventrice this morning going gang busters on things really popping soon in the Atlantic. Yet no signal in the models...Lets see if this changes soon.

He's been giving some mixed signals lately. Some tweets about positive MJO and CCKW and some tweets about suppressed phase late month into early Sept. It has been somewhat of a mixed bag from him that varies with analysis of overall models via the background state.

[WeatherEmperor]

It is possible the bulk of the hurricane season can occur from Sept - Nov. The 2001 season is a good example of that. I know the atmosphere and sst, etc are probably not a good analog for comparison to 2017 but it is good to understand. In 2001, June - August produced 4 tropical storms and 0 hurricanes. September - November produced 11 named storms including 9 hurricanes (4 major hurricanes).

Again, 2001 may not be a good analog in terms of atmospheric conditions but it is a recent example of a backloaded season. Perhaps something similar happens in 2017??

http://weather.unisys.com/hurricane/atl ... /index.php


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[WeatherEmperor]

https://twitter.com/MJVentrice/status/8 ... 3114261504

Ventrice talks about surpressed rainfall in the equatorial Pacific...but the graph he uses also shows some of the same in the ATL basin.


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[bubba hotep]

@EricBlake12
I'd even argue the first KW occurred in an unfavorable MJO state. The next one has more of a MJO signature, which to me means more impacts

 https://twitter.com/EricBlake12/status/895986597664923649

To add to Eric's point, the strongly suppressed phase of a CCKW moved across Africa prior to the "hype" wave that was supposed to set off the Atlantic.

 https://twitter.com/whatisthisrds/status/892523477701361665

[Ntxw]

That was the discussion we had here prior to the passage of the CCKW. It was the coming CCKW vs a less than stellar background state (this is evident globally as well).

We have to be careful not to overhype the CCKW imo. It is a great compliment to background conditions and is definitely a plus but you still have to consider there is still some shear and mid level dry air around the basin also which are more local conditions. The WPAC hasn't yet yielded a STY or has a major occured in the EPAC with this strong CCKW yet like some models have portrayed. Something in the background is not favorable globally. But it does help increase the chance of something forming in the coming days to weeks.

This is an interesting "test case" for what a strong CCKW can do. A very strong KW signal vs a somewhat unfavorable background. It'll be a fun few weeks in the tropics (at least for me since this fits right into my research interests).

In the end it was not the answer for everything (the first CCKW passage) but improved things some enough to wring out the first short lived Hurricane, but certainly no crazy outbreak

[Alyono]

Ventrice this morning going gang busters on things really popping soon in the Atlantic. Yet no signal in the models...Lets see if this changes soon.

He's placing far too much emphasis on Kelvin Waves. There are other factors as well.

His study did show a nice correlation. However, we also had that with the QBO winds. Last decade, additional research showed that the correlation broke down the year after Gray published his QBO paper.

Not sure if the Ventrice study examined this, but I'd be interested to see if there is a difference between Kelvin Waves in the Atlantic vs the Pacific. I ask because these equatorial waves that come into the Atlantic have to cross a very high mountain range in South America. I've long suspected these are far weaker in the Atlantic as a result

[RL3AO]

[

Not sure if the Ventrice study examined this, but I'd be interested to see if there is a difference between Kelvin Waves in the Atlantic vs the Pacific. I ask because these equatorial waves that come into the Atlantic have to cross a very high mountain range in South America. I've long suspected these are far weaker in the Atlantic as a result

This is the closest to what you're looking for. Fig. 5 breaks down by basin and equatorial wave. Kelvin wave doesn't quite reach the 99% confidence level in Atlantic as in the EPac. It shows the ER wave is the most impactful in the Atlantic (after the TD/MRG type of course). With ER being westward moving waves, I'm not sure if there are some impacts on that filtering band from easterly waves though.

I remember back to TD Four forming after a weak CCKW passed though. There was also a moderate ER wave signature too and we even had a low spin up near Brazil which matches up with the idealized ER wave.

http://journals.ametsoc.org/doi/abs/10. ... 11-00110.1