Typhoon Sonca

[Somerset Squall]

TD 19W has formed around 700 east of the island of Chichi Jima, Japan. 19W is in an area of moderate to high shear which is partially exposing the well defined LLC. Shear is expected to cap any significant intensity gains but 19W should become a tropical storm over the next few days.

19W should move northwestwards along the southwestern periphery of a subtropical ridge to the northeast. A break in the ridge is forecast to materialise in a few days time and allow 19W to recurve northeastwards well east of mainland Japan. Extratropical transition should occur at this stage as waters cool and shear remains high.

[Konstantinos]

Tropical Storm Sonca Tracking Map

Five Day Forecast Map

Edited September 15, 2011 by Konstantinos

[Somerset Squall]

Thanks for posting the track maps Konstantinos

Indeed, 19W has become Tropical Storm Sonca. Intensity rose to 40kts but has fallen back to 35kts this evening as dry air has been driven into the core of Sonca by moderate to high shear. Convection is very shallow in association with the LLC, and the banding features do not contain significantly deep convection either. Any strengthening will be slow due to the less than ideal environment. Sonca is not expected to become a typhoon before it recurves east of mainland Japan.

[Cookie]

A pretty system

[onlyME]

Of course,Cookie.

BTW,Sonca is now a Cat1 typhoon.

Convection is not very deep,but it is very well organized and the eye is distinct.

[Somerset Squall]

Dry air previously affecting Sonca has not been penetrating the core over the last 24hrs due to decreasing shear. Consequently, Sonca has strengthened to 65kts and has a fairly well defined eye embedded in a very small central dense overcast. Sonca is a small typhoon due to the dry air in the environment around it. Sonca is pretty near Chichi Jima and will deliver strong winds and heavy rains here. The typhoon is now moving northwestwards and is forecast to recurve into the westerlies east of Japan, and become extratropical in doing so. Poleward outflow is expected to improve briefly as Sonca heads to the north, which may allow some further intensification before shear increases and waters become cooler.

Yes, a very pretty typhoon Cookie, I agree. A tiny one though!

[Somerset Squall]

Sonca has strengthened to 75kts. The small typhoon is still exhibiting a small, well defined eye. Sonca has probably peaked as a recurve into the westerlies has began. This means shear will begin to increase and Sonca will also be moving over colder water, forcing the typhoon to weaken.

[onlyME]

Sonca still has well defined eye,but ring of convection around the eye is very thin.

Eyewall is weak on the northern side.

I cannot see much on WeatherUnderground's satellite animation because it's too fast,but it looks that Sonca is moving in NNE direction.

Edited September 18, 2011 by onlyME

[Somerset Squall]

Sonca has become a cat 2 typhoon with intensity rising to 85kts. The tiny typhoon continues to sport a well defined eye in a small central dense overcast, surrounded by dry air. Shear values rise significantly with lattitude, and will begin to impact Sonca later this evening.

[Cookie]

not looking bad at the moment

[cornishbrooksy]

what is the size estimate on Sonca? certainly a very small but very nice looking storm!

[Konstantinos]

When we say the size of a cyclone, what do we mean?

[cornishbrooksy]

Sorry, i meant diameter or radius from eye. Should have been clearer than that. Maybe its diameter of destructive winds...something to gauge how small this is in comparison to say an average size typhoon?

[Somerset Squall]

The current radius of tropical storm force winds is around 90 nautical miles. So quite a small typhoon in comparison to the usual West Pacific brutes. For example, Ma-on earlier in the year had tropical storm force winds extend 200 nautical miles from the centre, and Ma-on was by no means one of the largest typhoons.

[Somerset Squall]

Sonca became extratropical early this morning as it raced eastwards into the westerlies. Regeneration is not expected.