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Southern Hemisphere: Invest Thread 2009


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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

No invests.

South Pacific:

Shear has increased over 98P today, and all convection has been removed from the now entirely exposed LLC. As shear is forecast to remain strong, development is not expected.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

Invest 90S has formed, south of Diego Garcia. Deep convection is flaring along a trough located in the area. There is little evidence of convectional rotation as yet, so little evidence of an LLC. Shear is moderate to high in the region, so further development, if any, will be slow at best.

South Pacific:

98P has dissipated.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

90S has become slightly better organised today. Rotation is evident in the large area of convection and there are signs of weak banding on the southern and western sides of the disturbance. Shear is still high which will hinder further development.

Invest 91S has formed to the northwest of Madagascar. A rather shapeless area of deep convection has persisted for the last 12 hours, but it is being buffeted by strong shear. Further development will depend on the shear easing.

South Pacific:

No invests.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Thanks Cookie.

South Indian Ocean:

90S has dissipated.

91S has dissipated.

Invest 92S has formed to the east of where 90S dissipated. An ill defined LLC is surrounded by fragmented, disorganised convection. Moderate shear will dampen further development. Due to current disorganisation and unfavourable environment, chances for development into a TC are poor, at elast in the near term.

South Pacific:

No invests.

Edited by Somerset Squall
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

92S has dissipated.

Invest 94S has formed, in the central south Indian Ocean, several hundred miles southeast of Diego Garcia. Deep convection is flaring over an ill defined LLC. The disturbance is moving slowly southwards, towards colder waters. Shear is moderate over the system. Development will have to occur sooner rather than later as the system is not far from the cooler waters. The moderate shear might prevent this from happening.

South Pacific:

No invests.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

94S has rapidly moved south and is now over cold waters. In addition shear has now increased to destructive levels. Convection has vanished and the LLC is doing the same thing. Chances for developement are next to none.

Invest 95S has formed, the the north of the Northern Territories in the Arafura Sea. Disorganised convection is flaring in a broad area, but there is no sign of a defined LLC. Waters are warm but shear is moderate to high, so further development is not anticipated.

Invest 96S has formed, a few hundred miles north of La Reunion. Though waters are warm, very high shear (typical winter pattern) is preventing the LLC from organising and convection from forming. Unless the shear eases, chances for TC developent are poor.

South Pacific:

No invests.

Edited by Somerset Squall
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

94S is nothing but an exposed swirl of low clouds sinking south into the Southern Oceans. Development is not likely.

95S has become better organised overnight. Shear has lessened, and waters remain plenty warm enough for development. Convection is organising around a developing LLC, and the system is showing signs of developing outflow, indicative of a better defined system. I think there is a fair chance of this one developing into a TC next week.

96S has dissipated.

South Pacific:

No invests.

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Posted
  • Location: Tiree
  • Location: Tiree

95S

20090419.0430.gms6.x.ir1km.95SINVEST.15kts-1010mb-79S-1290E.100pc.jpg

TROPICAL CYCLONE OUTLOOK

TROPICAL CYCLONE OUTLOOK

FOR THE AREA BETWEEN LONGITUDES 125 EAST - 142 EAST

Issued by the BUREAU OF METEOROLOGY, DARWIN

at 2:15 pm CST Sunday 19 April 2009

A tropical low, 1006 hPa, is situated in the Timor Sea, about 500 kilometres

north of Darwin, near 8S 130E. The low is expected to remain slow moving over

the next three days, and may slowly develop.

The likelihood of a Tropical Cyclone occurring in the region in the next three

days is:

Monday: low,

Tuesday: low,

Wednesday: moderate.

NOTE: Development Potential is an estimate of the probability of tropical

cyclone development for each day... Low = 10% or less, Moderate = 20% - 40%,

High = 50% or more.

DARWIN Regional Forecasting Centre.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

94S remains insignificant. An entirely exposed LLC persists, but cool waters and high shear are preventing convectional flare-up. Chances for TC development are poor.

95S has become less organised this afternoon and evening. Convection is no longer wrapping around the LLC and is now fragmented and disorganised. The LLC remains fairly well defined. Some slow development is possible over the coming days.

South Pacific:

Invest 97P has formed, a hundred or so miles east-southeast of Brisbane. A non tropical low is tracking in an unusual direction, north, into the tropics. Warmer waters are allowing the system to slowly acquire tropical characteristics. Convection is attempting to wrap around a very well defined LLC. Shear is high but as this system started off extratropical west of New Zealand this isn't having much of a negitive effect on the LLC. However, convection is mostly lumped west of the centre. With such high shear in the region, development appears unlikely, however, if the shear lessens then the well defined LLC is already there for quick development.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

95S remains very disorganised. Shear is moderate, and land interaction with Indonesia has somewhat limited the system's organisation. There is little sign of a developed LLC, and chanches for development are poor at best.

South Pacific:

97P is drifting very slowly eastwards just north of 30S, on the edge of tropical waters. The system is unusually far south, and for this reason, though the LLC is well defined, there is little deep convection over the system due to marginal sea temps. Also a characteristic of subtropical waters this far south, and particularly as we head into Southern Hemisphere winter, shear is very high. The cirulation remains strong which leads me to believe this system is mostly extratropical, and this is probably backed up by the lack of really deep convection. There is some limited convection, and that's probably the only reason this low has been given invest status. Chances for development are poor unless the system lifts north into the tropics proper.

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Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL

We need to be careful with terminology here...

The system is almost certainly not extratropical, likewise it is almost certainly not tropical!

It is best described as subtropical.

It's not extratropical for two main reasons: it's warm cored, and there is no cold air on the western flank. Animated satellite images show it fairly well.....the western edge is being fed by the trade winds coming off northern New Zealand- these are not really transferring any cold air to it. The cloud pattern is boring old stratocumulus, clearly no open cell cumulus at all. If you tried to draw a cold front in there somewhere you would fail.

There's a subtropical analysis technique, which gives it an "ST" of 2.5, that is equivalent to winds of intensity 35-40knots near the centre. The idea is that if the cyclone acquired tropical characteristics (which it won't), it would becomes a DT2.5.

It will head slowly in a roughly southerly direction over the next few days, so no chance of tropical development. I would guess that SSTs up there at 30S are about 24C?

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

Indeed J07, bad terminology by me, I did say almost extratropical but of course the correct term is subtropical :D

South Indian Ocean:

95S has moved little in the last 24hrs. Convection is patchy and disorganised still, and is being hindered by dry air. Chances for development are poor.

South Pacific:

97P has dipped south of 30S, therefore is no longer considered suspect for tropical cyclone development.

Edited by Somerset Squall
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Posted
  • Location: City of Gales, New Zealand, 150m ASL
  • Location: City of Gales, New Zealand, 150m ASL

I was reading on another forum earlier about this system, some claimed that were it in the Atlantic it would have been considered a TC at some point.

http://www.storm2k.org/phpbb2/viewtopic.ph...59&t=105128

Anyway, yes it's not a risk of becoming tropical, and is forecast to very slowly progress south. We are still some way from it turning into an extratropical/mid-latitude low though.

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

95S remains unimpressive. Patchy convection is intermittantly firing near an ill defined LLC. The system has very slowly drifted eastwards. Shear remains moderate, and the atmosphere quite dry, surpressing further development.

South Pacific:

Invest 98P has formed in the northern Coral Sea, off the east coast of the Cape York Peninsula. Deep convection is flaring over a weak LLC. Moderate shear is impinging on the system, but waters are still warm enough in the region to support development. Slow organisation is possible over the coming days.

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Posted
  • Location: Tiree
  • Location: Tiree

95S

is getting its act together

TROPICAL CYCLONE OUTLOOK

FOR THE AREA BETWEEN LONGITUDES 125 EAST - 142 EAST

Issued by the BUREAU OF METEOROLOGY, DARWIN

at 2:15 pm CST Sunday 26 April 2009

A developing tropical low, 1005 hPa, is situated in the northern Arafura Sea,

near 8S 135E. The low is expected to move slowly northwest away from the NT

coast. The potential for development into a Tropical Cyclone has increased in

the past 24 hours.

The likelihood of a Tropical Cyclone occurring in the region in the next three

days is:

Monday: moderate,

Tuesday: moderate,

Wednesday: moderate.

NOTE: Development Potential is an estimate of the probability of tropical

cyclone development for each day... Low = 10% or less, Moderate = 20% - 40%,

High = 50% or more.

DARWIN Regional Forecasting Centre.

Tropical Cyclone Formation Alert

WTPS21 PGTW 260100

SUBJ/TROPICAL CYCLONE FORMATION ALERT//

RMKS/

1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN

A 200 NM RADIUS OF 7.8S 135.8E WITHIN THE NEXT 12 TO 24 HOURS.

AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CY-

CLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO

BE 25 TO 30 KNOTS. METSAT IMAGERY AT 260030Z INDICATES THAT A

CIRCULATION CENTER IS LOCATED NEAR 7.8S 135.8E. THE SYSTEM IS

MOVING EAST-NORTHEASTWARD AT 03 KNOTS.

2. REMARKS: THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 8.0S

136.0E, IS NOW LOCATED NEAR 7.8S 135.8E, APPROXIMATELY 410 NM NORTH-

EAST OF DARWIN, AUSTRALIA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY

INDICATES IMPROVED CONSOLIDATION WITH MULTIPLE DEEP CONVECTIVE BANDS

WRAPPING INTO A DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A

252204Z SSMI/S IMAGE DEPICTS CONVECTIVE BANDING WRAPPING FROM THE

WESTERN QUADRANT INTO THE EASTERN QUADRANT. RECENT SCATTEROMETER

DATA HAS BEEN UNAVAILABLE, HOWEVER, A 25/18Z SHIP REPORT FROM

VDRX2, LOCATED ABOUT 100 NM SSW, INDICATED WINDS OF 110/24 AND

SLP OF 1008.5 MB. THIS SUPPORTS THE ESTIMATED 25-30 KNOT MAXIMUM

SUSTAINED SURFACE WINDS. THE LLCC IS LOCATED JUST EQUATORWARD OF

THE UPPER-LEVEL SUBTROPICAL RIDGE AXIS UNDER MODERATE VERTICAL

WIND SHEAR, HOWEVER, ANIMATED WATER VAPOR IMAGERY SHOWS IMPROVED

POLEWARD OUTFLOW ENHANCED BY MIDLATITUDE WESTERLIES OVER NORTHERN

AUSTRALIA. ADDITIONALLY, SST, OCEAN HEAT CONTENT AND MOISTURE ARE

FAVORABLE FOR FURTHER DEVELOPMENT. TRACK MOTION HAS BEEN SLOW AND

ERRATIC BUT THE SYSTEM IS EXPECTED TO BEGIN TRACKING WESTWARD TO

NORTHWESTWARD WITHIN THE NEXT 24 HOURS. MAXIMUM SUSTAINED SURFACE

WINDS ARE ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE

IS ESTIMATED TO BE NEAR 1002 MB. THE POTENTIAL FOR THE DEVELOPMENT

OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS GOOD.

3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED

BY 270100Z.//

NNNN

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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

95S has become TC 27S.

Invest 99S has formed, south-southeast of Christmas Island. Fragmented convection is flaring to the east of an ill defined LLC. Moderate shear is preventing any rapid development. Waters are still warm enough to support development, but they shelve off and become much colder to the west. 99S has remained practically stationary over the last 24hrs. Slow development is possible if the system stays away from the cold waters to the west.

South Pacific:

98P has dissipated.

Edited by Somerset Squall
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Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

No invests.

South Pacific:

Invest 92P has formed, north of New Caledonia. Shear is low over the system, and waters are still warm enough for development. If the system can avoid turning south, then further development is likely. To the south lies cooler waters, and some very high shear, typical for this time of year in the south Pacific. The system is not moving much at the moment, perhaps a small southeastward drift in the last 24hrs. Whether this motion will continue is uncertain.

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  • 2 weeks later...
Posted
  • Location: Taunton, Somerset
  • Weather Preferences: Snow, thunder, strong winds
  • Location: Taunton, Somerset

South Indian Ocean:

Invest 93S has formed, northeast of Diego Garcia, just 3 degrees south of the equator. Deep convection is concentrating in the area and showing signs of weak rotation. 93S is in an area of moderate shear, but warm sea surface temperatures. Based on the current weak LLC, and moderate shear, chances for TC development in the near term are poor.

South Pacific:

No invests.

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