Severe Tropical Cyclone Dianne

[Somerset Squall]

TC 16S has formed to the northwest of Learmonth, Australia, with intensity at 35kts. The system is expected to move southwards and intensify. I'll have a full update later.

[Somerset Squall]

16S has strengthened to 40kts and has been named Dianne. Dianne is trapped in a weak steering environment and is moving very little. Ridging a long way south of the system is expected to break down to be replaced by a trough, and this trough should eventually pull Dianne southwards well west of the west coast of Australia. The environment is favourable for Dianne to strengthen, with low shear, good outflow and very warm sea temps. Dianne could become quite intense before meeting coolder water and higher shear on the southward track. Any eastward deviation in the track will put Exmouth at risk of gales, but land impact, at present, looks like it will be minimal.

[Somerset Squall]

Dianne has moved very little today and continues to be sandwiched between two ridges in a competitive steering environment. For the reason I explained in my last post, Dianne should begin to move southwards soon well west of the west coast of Australia.

Dianne has strengthened to 55kts. A central dense overcast feature has readily formed today, with impressive banding flanking the LLC. With low shear and very warm sea temps, further strengthening is likely until Dianne reaches cooler waters in around 48hrs time.

[Somerset Squall]

Dianne has strengthened further to 65kts. The cyclone is moving southwestwards at a faster pace, putting it at more of a distance from land. With favourable upper levels and warm waters persisting, Dianne should strengthen further and could get to around 100kts in intensity before colder waters induce weakening.

[Cookie]

[Somerset Squall]

Dianne has continued moving southwestwards whilst intensifying. The cyclone has been upgraded to a severe tropical cyclone by BOM, and intensity has risen sharply to 85kts, making Dianne a cat 2 on the SS scale. Dianne has developed a well defined eye embedded in a small central dense overcast, flanked by strong banding. Dianne has about another 24hrs to strengthen before the southwesterly to southerly track forces the cyclone over colder waters and higher shear, inducing weakening. Thereafter, extratropical transition should occur.

[Somerset Squall]

Dianne has moved faster than anticipated, and has reached cooler waters much sooner. Accordingly, Dianne has weakened since yesterday afternoon, with intensity falling to 70kts. Convection has become more shallow due to the reduced ocean heat content, but the eye is still clearly evident in satellite imagery. On the general southwest to southerly track over the next couple days, Dianne should weaken further and begin extratropical transition.

[Somerset Squall]

Dianne has moved out of the tropics and therefore has rapildy dissipated, with convection vanishing and the remnant low winding down.