Southern Hemisphere: Invest Thread 2009/2010

[Somerset Squall]

South Indian Ocean:

97S became TC 11S.

Invest 92S has formed in the Mozambique Channel, midway between the country itself and Madagascar, and about halfway down the channel. Deep convection is firing over a moderately defined LLC, which has shown some improvement over the last 12hrs. In addtition, it appears some weak banding is beginning to form. This is not surprising given that shear is low, waters are warm and 92S is developing dual outflow channels which will further tighten the LLC and enhance convection. I think there is a good chance of a TC forming here over the next few days.

South Pacific:

Invest 90P formed and became TC Oli.

Invest 93P has formed, aroudn 12S, 150W, several hundred miles east of TC Oli. This invest is quite a long way east in the South Pacific basin and is no threat to large landmasses. Convection is disorganised at present though is showing signs of weak rotation. The environment is good, with low ahear and warm sea surface temperatures. Shear rises dramatically to the south, but if 93P can avoid this then some slow development could occur.

Edited February 1, 2010 by Somerset Squall

[Somerset Squall]

South Indian Ocean:

92S became TC Fami.

Invest 96S formed a couple days ago and has been unimpressive so far. However, convection has been steadily increasing today around an LLC located near 12S, 90E. Shear is currently low over the system, and sea temperatures are warm. Therefore further development appears likely if conditions remain favourable.

South Pacific:

Invest 93P dissipated.

Invest 98P has formed around 12S 172W. The invest appears to be rapidly organising, in a similar vain to the formation of TC Pat. A well defined mid-level circulation is evident, with deep convection continually building in the vicinity of the centre. Once the circulation extends to low levels, a tropical cyclone could rapidly form as the system is already showing some impressive spin. Shear is low and waters are warm, the only complication being TC Pat to the southeast, however, interaction between the two systems is considered unlikely at present. I think there is a fair chnace of this system becoming a tropical cyclone over the next couple days.

[Somerset Squall]

South Indian Ocean:

96S has become less organised over the last 24hrs. Convection has decreased, and rotation is weak. The disturbance could easily dissipate at any time. Chances for development are poor.

South Pacific:

98P seems to be the verge of becoming a tropical cyclone. Curved banding is wrapping well around the tightening LLC, though the convection directly over the centre is currently lacking. This will have to be rectified before further intensification can occur. However, conditions look set to remain favourable, so there is a good chance of this one becoming a tropical cyclone.

Invest 99P has formed several hundred miles west-northwest of 98P, around 10S 171W. Convection is steadily increasing and showing signs of rotation around a developing LLC. Shear is low and water temps are in excess of 30C. In addition, upper level outflow is also good. With the good environment and early signs of rotation, there is a fair chance this system will become a tropical cyclone in the next few days.

[Somerset Squall]

South Indian Ocean:

96S dissipated.

Invest 91S has formed a couple hundred miles north of the island of St. Brandon, east of Madagascar. Both JTWC and MeteoFrance are keen to make this one a tropical cyclone within the next 24hrs. Satellite imagery shows why, with deep, persistant convection located over a tightening LLC. Conditions are good for further development, with low shear and warm sea temps.

Invest 92S has formed, much farther to the east. Deep convection is pulsing over an ill defined LLC, but is not showing any persistance. Moderate shear could slow further development.

South Pacific:

98P became TC Rene.

99P dissipated.

[Somerset Squall]

South Indian Ocean:

91S became Intense Tropical Cyclone Gelane.

92S dissipated.

South Pacific:

Invest 94P has formed, 550 miles northeast of Pago Pago, at 6S, 162W. Deep convection is gradually becoming more persistant over a consolidating LLC. 94P is in a favourable environment for further development, with low shear, warm sea temps and good upper level outflow which should further enhance the convection and tighten the LLC. JTWC give this system a fair chance of becoming a TC in the next 24hrs, and there is a good chance it seems beyond this.

[Cookie]

92P

[Somerset Squall]

South Indian Ocean:

Invest 90S is located just off the east coast of Madagascar. The invest has lingered here for the last few days with little development. The system is bring heavy rainfall to central and eastern Madagascar. Through the day, stronger rotation has been evident within the convection which may be indicative of a circulation trying to form. In addition, convection is slowly increasing. Waters are warm beneath 90S, and shear is low to moderate. These factors support further development, but a complicating factor is land interaction, which could slow or even stop development, particularly if the disturbance travels any further to the west. I think there is a 30% chance of this system becoming a tropical cyclone within the next 24hrs, and the chances may increase slightly if the invest moves to the east.

Invest 94S has formed at 14S 76E, several hundred miles south-southeast of Diego Garcia. Deep, flaring convection is showing signs of rotation around a weak LLC. Shear is low, and waters, for now, are warm. However, waters cool significantly to the south which could hinder long term development. However, the environment appears conducive for some slow development of this disturbance over the next few days.

South Pacific:

Invest 92P is an unimpressive invest which consists of messy convection with little rotation or organisation. Moderate to high shear is preventing convection from persisting or for any circulation centres to become stacked to form a tropical cyclone. Waters are warm, but unless the upper level environment improves, further development potential is low.

[Cookie]

90S

[Somerset Squall]

South Indian Ocean:

90S has drifted southeastwards away from land and has become much better organised over the last 24hrs. Convection is not that substantial presently, but what is evident is a strong LLC. As soon as the convection increases further, a tropical cyclone could form. JTWC have issued a TCFA on the system, and MeteoFrance are keen on developing the system too. Future steering is uncertain, but MeteoFrance, despite the current southeasterly track, are favouring a westward heading which would only support a short lived tropical cyclone before landfall on the east coast of Madagascar.

94S has dissipated.

South Pacific:

92P has dissipated.

Invest 97P has formed to the east of where 92P dissipated. High shear is disrupting development of this highly disorganised invest. Development, if any in the shear, will be slow to occur.

[Cookie]

90S

[Somerset Squall]

South Indian Ocean:

90S became Tropical Cyclone Hubert.

South Pacific:

97P, against forecasts, developed into Tropical Cyclone 19P as the environment rapidly improved.

Invest 98P has formed to the west of TC 19P, to the north of Vanuatu. Deep convection is persisting over an increasingly well defined LLC and the JTWC have issued a tropical cyclone formation alert on the system. Shear is low, sea temps warm and equatorward outflow good which supports further development. If organisational trends continue, this one could be declared a tropical cyclone later tonight or early tomorrow.

[Somerset Squall]

South Indian Ocean:

Invest 90S has formed around 6S 86E, just in the Australian region of responsibilty. At present, 90S consists of a weak region of turning within an area of disorganised, limited convection. For this reason, any further development is likely to be slow. However, conditions are favourable for further development with low shear and warm sea temperatures in the surrounding area.

South Pacific:

98P became Severe Tropical Cyclone Ului.

[Cookie]

90S

[Somerset Squall]

South Indian Ocean:

90S became Tropical Cyclone Imani.

Invest 92S has formed around 7S 70E. The system is quite broad at present, with disorganised yet deep convection showing signs of weak rotation around several possible circulations. Shear is moderate to high (20-30kts), which is probably disrupting any formation of a strong LLC. Waters are very warm however, fuelling the deep convection currently present in association with 92S. If 92S can move southwards, it will find lower shear values, however, if it moves too far south, it will reach cooler waters. Unless shear eases where 92S is now, then development could be slow or not occur at all. I give this system a poor chance of becoming a TC in the next 24hrs, as there is only a small area of favourable conditions to the south of the system at present.

South Pacific:

Invest 91P has formed off the north coast of Australia, in the Arafura Sea. 91P is a disorganised monsoonal system with plenty of deep convection but only weak rotation at present. JTWC haven't picked up this system at all really, though BOM are very keen on it becoming a tropical cyclone in around 36hrs time as it moves towards the Gove coastline. Waters are very warm, and shear is low, so consolidation seems possible but whether a tropical cyclone can form out of this disorganised system within the 48hrs before landfall in Gove remains to be seen. Communuties from Maningrida eastwards to Nhulunbury need to be weary of this system even if it doesn't become a tropical cyclone, as there is likely to still be some extremely heavy rains from this system. If this system doesn't develop before landfall in around 48hrs time, then it still needs watching as it is forecast to move southeastwards where it could emerge into the Gulf Of Carpentaria, where conditions are currently favourable. It's a long way off, but Queensland also need to monitor this system because if it indeed develops in the Gulf Of Carpentaria, a continued southeasterly motion seems likely judging by model predictions, which could bring further flooding rains to areas affected by Severe TC Ului at the end of last week. A lot to keep an eye on!

[Cookie]

91P

this could really be an intresting one to track.

[Somerset Squall]

South Indian Ocean:

92S dissipated.

Invest 94S has formed, at 10S 93E, around 260 miles west-northwest of the Cocos Islands. An area of deep convection has been expanding through the day near an increasingly well defined LLC. Conditions are favourable for further development as shear is low and waters are warm. JTWC give 94S a fair chance of becoming a tropical cyclone within the next 24hrs.

South Pacific:

91P became TC Paul.

Invest 95P has formed around 19S 172E. The invest is little more than scattered convection showing no real signs of rotation. The system formed yesterday and does not look as impressive as then. As the system appears to be losing organisation, the chances for TC formation are poor.

[Somerset Squall]

South Indian Ocean:

94S became TC Robyn.

Invest 99S has formed around 10S, 103E, in the eastern South Indian Ocean. Messy, limited convection is showing signs of weak rotation. Most of this system's energy is probably being stolen by a larger invest to the east. Chances for TC development are poor.

Invest 91S has formed several hundred miles north of Port Hedland, Western Australia. A large and deep area of convection is expanding over a consolidating LLC. With toasty waters, low shear and good outflow, further development is expected with a fair chance of the system becoming a TC within the next 24hrs according to JTWC.

South Pacific:

No invests.

[Cookie]

about time to from the SIO

[Cookie]

94P

Has formed and is looking quite organized already.

[Somerset Squall]

South Indian Ocean:

No invests.

South Pacific:

So, 94P, interesting little system this. It has formed at 30S, and you can see from the imagery it is not far off the north island of New Zealand. Tropical cyclone formation is practically unheard of at this lattitude, which makes me think if this one is to develop at all it will be subtropical at very best. Waters are cool here, and it is surprising given that it's fast approaching Winter this side of the equator that this system has found shear low enough to develop. What I expect has happend (I haven't been watching this area over the last few days), is that an extratropical low has become cut off from the baroclinic zone, and these lows are found to be more resistant to shear. It will be a bit of a miracle if this one becomes a fully fledged tropical cyclone however.

[Cookie]

94P

something to watch anyway. interesting little system all the same.

[Somerset Squall]

Moving south and dissipating...

[J07]

94P was classified a ST2.5 using the Poteat Subtropical technique a few days ago. (Basically the same as Dvorak, but for subtropical cyclones). ST2.5 corresponds to DT2.5, which has a core of winds 35-40kts, aka a tropical cyclone.

Within the next 24 hours it will complete its transition to an extratropical cyclone, as cold air from near Australia pushes up its western flank.

Where did it come from in the first place? There was a pre-existing trough in the Coral Sea, about 25-30S. A weakening front transported this eastwards, where it sat stationary northwest of the North Island, deepening quite nicely. It developed some good banding over time. SSTs are approximately 23C there.

Subtropical cyclones are not too uncommon in such waters during autumn. They don't always form as this one did, sometimes a tropical cyclone will fail to make ET transition and instead become subtropical, before finally moving off to the south and developing the standard ET features of a fairly clear warm and cold front set.

[Somerset Squall]

South Indian Ocean:

Invest 95S has formed around 300 miles north-northeast of the Cocos Islands. Deep convection is persisting over a consolidating LLC. Shear is low and waters are still warm, and outflow is also good. This could support further development over the next day or so. If the invest keeps to it's current trend of organisation then there is a fair chance a tropical cyclone could form.

Invest 97S has formed near Diego Garcia. Deep convection is flaring and showing signs of broad rotation. Shear is low over the disturbance, and at a lattitude of 6S, waters are still pretty warm. The LLC is at best very broad at the moment but the conditions do support at least some slow development.

South Pacific:

94P is now fully extratropical to the southwest of New Zealand.

[Somerset Squall]

South Indian Ocean:

95S has remained in a steady state over the last few days. The invest has moved eastwards towards Indonesia. Convection has been flaring near the LLC but has lacked persistance. In addition, the LLC has weakened a bit since when I last posted. Waters are still warm and shear low to moderate, so I still think there is a fair chance this one could eventually become a tropical cyclone.

97S has been moving eastwards too and has not got any better organised than before. Like with 95S, convection has come and go over the last 48hrs and the LLC is still broad. Shear is still not too high so some slow development may still occur over the next day or so.

South Pacific:

No invests.