Tropical Cyclone 11S

[Somerset Squall]

After a two week slumber, the South Indian Ocean has awoken with the formation TC11S, which formed from invest 97S. 11S is located around 300 miles northeast of La Reunion. Intensity is 35kts currently, and 11S is exhibiting some fairly deep convection over the centre with banding wrapping from the east into the southern quadrant of the storm. 11S has some opportunity to strengthen, but only for about another 24-36hrs. Shear is low and waters are warm currently, but the waters get significantly cooler on the southward track beyond 36hrs. 11S will move along the western periphery of a subtropical ridge to the east. Eventually, 11S should curve southeastwards influenced by mid-lattitude westerlies, and at this point extratropical transition should begin as shear increases. I only expect a peak of around 40-45kts, unless 11S really makes use of the short while it has in a favourable environment.

[Somerset Squall]

11S is going through an interesting evolution right now. The system has failed to strengthen due to the presence of a cold cored upper level low which resided to the southwest of 11S and has now swung to the northwest. The effect the low has had on 11S is rather complex, but the bottom line is it has been advecting cold, dry air into the circulation of 11S which has caused an overall decrease in convection, and a reduction in intensity to 30kts. Additionally, the LLC of 11S remains warm cored, but at the upper levels the core is analysed as cold, and therefore MeteoFrance has declared 11S as subtropical, and JTWC also suggest that 11S as transitioned into a subtropical depression. The LLC is entirely exposed, and the strongest winds are removed to the southern quadrant of the circulation, adding further credence to the subtropical classification. The upper level low is expected to move away, but by this time the subtropical depression will have moved over colder waters, which is likely to initiate a quick extratropical transition. During this transition to a fully cold cored system, 11S is likely to intensify to storm strength as the low is enhanced by spin created by the belt of mid-lattitude westerlies to the south of 11S.

Looks a beauty on satellite imagery (exposed LLC's often are):

[Somerset Squall]

11S is now fully extratropical. As expected, the depression has remained well defined through the transition.