Sunday, October 30, 2011

Latest on AS-2: Updated 7.00pm IST Sunday.

Positioned at 6.00 pm IST, Sunday, at 14.7N and 58.9E. Movement in last 6 hrs : Slightly North.
Even though IMD terms it as a depression, being at 1006 mb now, after dropping to 1004 mb, its not gaining too much strength as such. Winds maintained at 20 knts.
Having a constant NW track, the clouding is apparently moving away from the Karnataka and Konkan coast (and away from Mumbai).

AS-2 will now move NW, and approach the South coast of Oman. As explained in earlier blog, may curve N later due to jet streams direction and wind shear, but as a weaker system. On skirting the Oman coast, it seems the system will weaken rapidly.

The Southern UAC is just South of the Southern tip of India. Clouding accumulated along the Kerala coast and Southern tip is due to this system.
System will gain, and will be numbered when the system descends to a sea level low by Tuesday. Expected to move NW, and cross into the Arabian Sea.


svt said...

Which are the various factors that affects movement of tropical system? What exactly is needed for current UAC (after its intensifies) around Kerala to move northward or northeast wards as it happend with Cyclone Phyan in November 2009. I'm confused with this. Plz Explain.

sset said...

Seems this NEM, cloud cover is not covering entire TN/Rayalseems/south interior karnataka - cloud mass is failing to travel upwards - some force/current is lacking. If it moves eastwards into Arabian sea, then again same pattern as AS2 depression or 2009 phyan may occur. So where is the UAC /depression over TN has predicted early during 31oct-1stNov -seems this may not happen.

Also AS2 seems to avoid Oman and fallback to Pakistan/Karachi with little signs of weaking, infact this may turn clockwise - pakistan/Rajisthan - re-emerge.

Current south probable UAC may start feeding AS2 depression to seed another whirl over Arabian sea - In all such circumstances TN may miss much requried rain.

Rajesh sir will explain us correct technical language.

rajesh said...

svt: When a system moves in the sea, there are several factors which guide its movement and strength. and not always the same factor will have affect a storm in the same way.Depends on the correlated situations. Factors which influence a storm, in different ways are, Upper jet streams, wind shear, SST, lower winds and sometimes the upper ridge. All depends.

sset: AS-2 is expected to move towards Oman and then curve towards North like I explained. Its clouding will spread as it then weakens with the jet streams.
The UAC can move NW and emerge in the A.Sea. At present it is drawing the cloudings from the North T.N. region. I have said we will wait for its coming into the western sea and then track it, if it strengthens.
anyway, please comment on Nov. forecast when i put it up tomorrow.

nr said...

When will the November forecast be put up?

Viravanalluran said...

[1] The lower wind speed shear will indicate [i.e Upper wind speed-lower wind speed]the vertical development or strong convective activity.
[2] The guiding 200hPa upper wind may sometimes drag the system in its course.
[3] Sea Surface Temperature is important for convective activity.
[4] The strength of the prevailing wind regime {SWlY OR NEly] many a time determine the course of the storm track
[5] The continuous weather activities in a particular sea surface area

svt said...

@Rajesh @viravanalluran Thanks. Early indications are that even next Low/Dep will move northwest wards. Hopefully forecasts changes in next few days.

junaid said...

@svt,,,,,i too hope that the forcasts change and the uac on intensifying affects mumbai and surrounding as the north konkan coast is suffering from high max temps of the range 34-36 and the nyts r also warm.....and this spillover ne monsoon rain shud definitely com to us !!!!rather than going to karachi or oman,,,,as chennai also got excess rain during aug and sept!!now its our turn ..:) :) :) :) :)

Viravanalluran said...

Some light on wind sped shear for readers:
CIMSS Tropical Cyclone Team
Atmospheric Motion Vectors (AMV) - Product Description

Atmospheric Shear

Background: Using the gridded atmospheric motion vector output u and v AMV components are averaged over an upper layer (150, 200, 250, 300, and 350 hPa) and a lower layer (700, 775, 850, and 925 hPa). The difference in these averaged components is used to compute the speed shear between the upper and lower layers. The contours show the vector magnitude shear (absolute value). The streamlines indicate the direction of the shear.

In the case when a tropical cyclone (TC) is present, the analyses are modified in the storm region by a procedure which removes the storm circulation within a prescribed radii. This allows a more representative depiction of the environmental shear acting on the storm.

Uses: The presence/lack of atmospheric wind shear is vital to hindering/supporting TC development. A low shear environment is favorable for tropical cyclone development, while a high shear environment will deter a immature TC region from (further) developing or destroy an already mature TC. Shear values below 10 m/s (20 kts) are considered low enough for tropical cyclogenesis.

rajesh said...

Thanks Viravanalluran for the detailed explanation.Readers benefit regularly from your inputs. Please keep them coming.