Possible subtropical cyclone off South Africa?

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Coredesat

Possible subtropical cyclone off South Africa?

#1 Postby Coredesat » Sun Mar 18, 2007 9:08 pm

I can't take credit for first noticing this (that should go to Chacor), but there's a really interesting low off South Africa. It looks almost subtropical in nature:

Image

The 18z models also indicate that it has a shallow warm core:

GFS - http://moe.met.fsu.edu/cyclonephase/gfs ... 18/10.html
UKMET - http://moe.met.fsu.edu/cyclonephase/ukm ... 18/24.html

The 12z CMC shows it with a cold core, and the 12z NOGAPS makes it appear to be ex-Indlala (which, when compared to the other tracks, seems kind of odd).
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#2 Postby HURAKAN » Sun Mar 18, 2007 9:22 pm

Image

There is the strong non-tropical system. It seems to be still attached to a cold front, but nevertheless, it looks powerful just by looking how close the isobars are.
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#3 Postby Chacor » Sun Mar 18, 2007 9:24 pm

Latest synoptic chart from South Africa:

[web]http://www.weathersa.co.za/ship/ship.gif[/web]
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#4 Postby Chacor » Mon Mar 19, 2007 1:43 am

Philippe Caroff of Met-France has kindly responded (within 4 hours!) to my email regarding this (well, to be more precise, regarding the boundaries of MF's warning area, which I thought was up to 30S, but it's apparently been extended to 40S).

It seems that, according to him, this system had baroclinic origins, but it was in warm waters, therefore convection developed, and he feels that transition to a subtropical cyclone is not impossible, and I quote, "in this case we might decide to warn on it".
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#5 Postby Coredesat » Mon Mar 19, 2007 1:50 am

Looking good at 06Z:

Image
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#6 Postby MississippiHurricane » Mon Mar 19, 2007 2:46 am

This brings up a question.....has a system ever crossed into the Atlantic from this side of Africa?
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#7 Postby Coredesat » Mon Mar 19, 2007 3:45 am

As far as I know, no. From what I can tell, cyclones either dissipate inland over southern Africa or recurve southeastward and out to sea, though there has been at least one that came close:

Image

They wouldn't survive long on the other side due to shear and marginal SSTs, and they wouldn't be able to round the tip due to the subtropical westerlies.
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#8 Postby HURAKAN » Mon Mar 19, 2007 8:45 am

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#9 Postby AJC3 » Mon Mar 19, 2007 12:37 pm

Also, cyclone Leon-Eline (2000) made a very deep westward penetration into southern Africa. Don't have time to expand further upon this, but Google it - there's a ton of info about it on the web.
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#10 Postby P.K. » Mon Mar 19, 2007 4:19 pm

When, if ever, did RSMC La Reunion last warn for a subtropical system. I know the operational manual contains the phrase "subtropical disturbance" but that is it and it certainly isn't mentioned on their public page on the types of systems.
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#11 Postby Chacor » Mon Mar 19, 2007 8:49 pm

P.K. wrote:When, if ever, did RSMC La Reunion last warn for a subtropical system. I know the operational manual contains the phrase "subtropical disturbance" but that is it and it certainly isn't mentioned on their public page on the types of systems.


I'm not sure, that's why I asked if they would warn on it.
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#12 Postby Meso » Tue Mar 20, 2007 4:58 am

Hah,this storm created some really big swells off the coast of Durban,doing lots of damage to the beaches and areas there was a spring high tied accompanied with the cut off low it was pretty huge.

What this was,was a cold front supported with sharp trough that developed into a cut-off low which remained stationary for a while.See a few of them every few years.This one deepened a bit more than usual though

Here is a short local press release on it : http://www.weathersa.co.za/Pressroom/20 ... r20KZN.jsp

Article : http://www.news24.com/News24/South_Afri ... 47,00.html

And here is what AJC3 was talking about : http://www.weathersa.co.za/Pressroom/20 ... CEline.jsp
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#13 Postby Coredesat » Tue Mar 20, 2007 7:46 am

Looks to be in the process of becoming fully extratropical again. It's got a better-defined front and is becoming elongated:

Image
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#14 Postby Chacor » Tue Mar 20, 2007 9:00 am

Interestingly, SAB issued one Hebert-Poteat classification, at 0900Z today:

20/0900 UTC 34.5S 36.7E ST2.5/2.5 99S -- South Indian Ocean

WWIO21 KNES 200935
SATELLITE WEATHER BULLETIN
SOUTH INDIAN OCEAN MET-7 VIS/IRDAY
.
MARCH 20 2007 0900Z
.
34.6S 36.7E ST2.5 SUBTROPICAL DISTURBANCE
.
PAST POSITIONS....NEWLY DEVELOPED DISTURBANCE
.
REMARKS....FLORIDA STATE UNIVERSITY CYCLONE PHASE DIAGRAMS BASED
ON 00Z MAR 20 RUN OF THE GFS INDICATE THE SYSTEM SOUTH SOUTHWEST
OF MADAGASCAR POSSESSES A NOMINAL SHALLOW WARM CORE STRUCTURE.
CONSISTENT WITH SUBTROPICAL SYSTEMS MOST OF THE CONVECTION IS
LOCATED EAST AND POLEWARD OF THE CENTER...BY 1 TO 1.5 DEGREES
LATITUDE. QUIKSCAT DATA FROM 0336Z SUPPORTS AN INTENSITY OF 35-
40 KNOTS.
.
POSITION ACCURATE WITHIN 40 NMI
.
THE NEXT BULLETIN WILL BE ISSUED BY 20/1600Z.
.
FOR AREAL DISPLAY OF RAINFALL POTENTIAL SEE OUR WEB SITE AT
HTTP://WWW.SSD.NOAA.GOV/PS/TROP/TRAP-IMG.HTML
ALL LOWER CASE LETTERS EXCEPT PS/TROP
.
TURK
.
NNNN
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#15 Postby Coredesat » Tue Mar 20, 2007 9:30 am

Actually, it still looks fairly good on Reunion's satellite imagery. The angle of the EUMETSAT image threw me off.
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#16 Postby Chacor » Tue Mar 20, 2007 10:07 am

20/1430 UTC 35.6S 37.0E ST2.5/2.5 99S -- South Indian Ocean

WWIO21 KNES 201500
SATELLITE WEATHER BULLETIN
SOUTH INDIAN OCEAN MET-7 VIS/IRDAY
.
MARCH 20 2007 1430Z
.
35.6S 37.1E ST2.5 SUBTROPICAL DISTURBANCE
.
PAST POSITIONS....34.6S 36.7E 20/0900Z IRDAY/VIS
.
REMARKS....FLORIDA STATE UNIVERSITY CYCLONE PHASE DIAGRAMS BASED
ON 00Z MARCH 20 RUN OF THE GFS INDICATES THE SYSTEM SOUTH
SOUTHWEST OF MADAGASCAR POSSESSES A NOMINAL SHALLOW WARM CORE
STRUCTURE. CONSISTENT WITH SUBTROPICAL SYSTEMS MOST OF THE
CONVECTION IS LOCATED EAST AND POLEWARD OF THE CENTER...BY 1-1.5
DEGREES LATITUDE.
.
POSITION ACCURATE WITHIN 40 NMI.
.
THE NEXT BULLETIN WILL BE ISSUED BY 20/2200Z
.
FOR AREAL DISPLAY OF RAINFALL POTENTIAL SEE OUR WEB SITE AT
HTTP://WWW.SSD.NOAA.GOV/PS/TROP/TRAP-IMG.HTML
ALL LOWER CASE LETTERS EXCEPT PS/TROP
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KIBLER
.
NNNN
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#17 Postby HURAKAN » Tue Mar 20, 2007 3:50 pm

20/1900 UTC 36.0S 37.1E ST2.5/2.5 99S -- South Indian Ocean

Dvorak continues to make estimates.
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#18 Postby Chacor » Tue Mar 20, 2007 9:10 pm

Doesn't look as good now. SAB still hasn't issued a bulletin for their 19Z ST fix, weirdly enough.
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#19 Postby HURAKAN » Wed Mar 21, 2007 8:01 am

21/0830 UTC 36.6S 38.5E ST2.5/2.5 99S -- South Indian Ocean

Still subtropical.
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#20 Postby P.K. » Wed Mar 21, 2007 5:14 pm

It was given a ST2.5 this afternoon but is down to ST1.5 with this being the last bulletin.

SATELLITE WEATHER BULLETIN
SOUTH INDIAN OCEAN MET-7 IRNIGHT
.
MARCH 21 2007 1900Z
.
36.6S 41.0E ST1.5 SUBTROPICAL DISTURBANCE
.
PAST POSITIONS...36.6S 38.5E 21/0830Z VIS/IRDAY
35.6S 37.1E 20/1430Z IRNIGHT

.
REMARKS...SYSTEM CONTINUES TO WEAKEN. LOCATED LOW LEVEL
CIRCULATION WITH THE AID OF QUIKSCAT WINDS.
.
POSITION ACCURATE WITHIN 60 NMI.
.
THIS IS THE FINAL BULLETIN.
.
FOR AREAL DISPLAY OF RAINFALL POTENTIAL SEE OUR WEB SITE AT
HTTP://WWW.SSD.NOAA.GOV/PS/TROP/TRAP-IMG.HTML
ALL LOWER CASE LETTERS EXCEPT PS/TROP
.
BROWN
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