Southern Hemisphere: Invest Thread 2009

[Somerset Squall]

South Indian Ocean:

Convection associated with 93S has increased overnight, however, it's become less organised. There are little or no signs of any LLC, and though the convection is deeper and more widespread, it's not concentrated in any one area. Moderate to high shear is effecting this system, which makes the chances for TC development unlikely.

Invest 94S has formed to the north-northwest of Madagascar. Convection is flaring up quite nicely in the area, but the system lacks a LLC. Shear is currently low to moderate, but increases dramatically to the south. As the system currently lacks a well defined LLC, and there is only a small area of low shear, then chances for TC development in the near term are poor.

South Pacific:

No invests.

[Somerset Squall]

South Indian Ocean:

93S has dissipated.

94S has dissipated.

South Pacific:

Invest 95P has formed, near the Solomon Islands. A large expanse of showers and thunderstorms is persisting in the area, and is showing signs of rotation indicating a possible circulation, or mulitiple circulations. The disturbance as a whole is moving southeastwards. Shear is currently low over 95P, but increases to destructive levels to the south. I don't think this system will have time to develop into a TC before it slips southeastwards into the high shear.

[Somerset Squall]

South Indian Ocean:

Invest 90S has formed in the central South Indian Ocean, a few hundred miles southeast of Diego Garcia. Tropical disturbances are rare in this basin in August, but not unheard of. Deep convection is exploding in the area, and is showing signs of weak rotation suggesting there is a weak circulation. However, this circulation probably doesn't extend to the surface and is probably mid to high level. Sea temperatures are marginal, and rapidly cool further south. Current motion is high to gauge without a significant circulation though it looks like the disturbance as a whole is moving southwestwards. Chances for TC formation are poor if this motion continues.

Image below clearly shows 90S

:

South Pacific:

No invests.

[Cookie]

91S?

I might be wrong with this one

ABIO10 PGTW 161800

MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//

SUBJ/SIGNIFICANT TROPICAL WEATHER ADVISORY FOR THE INDIAN

/OCEAN/161800Z-171800ZSEP2009//

RMKS/

1. NORTH INDIAN OCEAN AREA (MALAY PENINSULA WEST TO COAST OF AFRICA):

A. TROPICAL CYCLONE SUMMARY: NONE.

B. TROPICAL DISTURBANCE SUMMARY: NONE.

2. SOUTH INDIAN OCEAN AREA (135E WEST TO COAST OF AFRICA):

A. TROPICAL CYCLONE SUMMARY: NONE.

B. TROPICAL DISTURBANCE SUMMARY:

(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 3.3S 95.8E,

IS NOW LOCATED NEAR 3.8S 94.6E, APPROXIMATELY 1340 NM EAST OF

DIEGO GARCIA. RECENT ANIMATED MULTISPECTRAL SATELLITE IMAGERY

INDICATES SLOW CONSOLIDATION OF A LOOSELY ORGANIZED AREA OF

CONVECTION PERSISTING OFF THE WESTERN COAST OF SUMATRA. A 160659Z

AMSU-B MICROWAVE IMAGE DEPICTS DEEP CENTRAL CONVECTION FLANKING THE

WESTERN PERIPHERY OF A WELL-DEFINED, AND PARTIALLY EXPOSED, LOW

LEVEL CIRCULATION CENTER (LLCC). A 152338Z QUIKSCAT IMAGE SUGGESTS

THAT WINDS MAY BE AS HIGH AS 15 TO 20 KNOTS AT THE CENTER. DESPITE

AN IMPROVED CONVECTIVE SIGNATURE AND WELL-DEFINED LLCC, VERTICAL

WIND SHEAR IN EXCESS OF 40 KNOTS WILL BE A LIMITING FACTOR IN

FURTHER CONSOLIDATION AND STRENGTHENING. MAXIMUM SUSTAINED SURFACE

WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS

ESTIMATED TO BE NEAR 1008 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A

SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS POOR.

(2) NO OTHER SUSPECT AREAS.

FORECAST TEAM: DELTA//

NNNN

[Somerset Squall]

Nope, you're right Cookie.

South Indian Ocean:

90S dissipated.

As Cookie has mentioned, invest 91S has formed a few hundred miles west of Sumatra. JTWC states the system is being battered by heavy shear, and looking at CIMSS wind shear charts the shear is around 30kts currently. 91S has put up an impressive fight against the shear, by maintaining a deep area of convection just west of a partially exposed LLC. The LLC has got a little better defined over the last 24hrs. Slightly lower shear values are present to the west, but it is unclear whether 91S will find them as it is moving southwestwards. Waters are sufficiently warm to support TC formation but do generally decline south of 5S (the invest is around 3.5S currently). Blending all these facts together, I agree with JTWC that chances are poor for TC formation, but if 91S continues to organise in the face of the shear I may have to re-assess that judgement.

South Pacific:

No invests.

[Somerset Squall]

South Indian Ocean:

Shear has eased a little over 91S, and convection has become a little more centralised. JTWC have upgraded the chances of TC development within the next 24hrs to fair, and TCWC Jakarta are also forecasting a moderate risk of devleopment. Based on how well 91S has coped with shear so far, the easing of the shear may allow this system to develop into a tropical cyclone within the next couple of days.

South Pacific:

No invests.

[Cookie]

91S image

[Somerset Squall]

91S had lost all convection due to shear and wasn't considered a candidate for development over the last day or so. However, convection has made a significant comeback today, and 91S is finally approaching a more favourable environment. 91S is slowly heading west-southwestwards into a region of low shear, and is also moving over an area of very warm waters (around 28-29C). These factors favour development, and I give 91S a fair chance of TC development over the next couple days.

[Somerset Squall]

South Indian Ocean:

91S dissipated a few days after my last post.

South Pacific:

Invest 96P has persisted over the last few days a hundred miles or so west of the Solomon Islands. Only now has the disturbance looked more interesting. Convection is flaring over an area of pronounced turning evident in satellite imagery. Shear is moderate, and sea temps are warm. In addition, poleward outflow is good which should aid the spin up of a circulation. The system still has a lot of work to do, and chances of development of a TC in the near term is poor, but I may re-evaluate that asessment if an LLC forms.

Invest 97P is persisting around 7N, 177E. Deep convection is firing in the area, but is showing little sign of rotation. Closeness to the equator is probably a limiting factor, despit warm sea temps and low shear. For this reason, chances of TC formation are poor.

Edited October 22, 2009 by Somerset Squall

[Cookie]

things will be picking up again in the southern Hampshire soon.