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Somerset Squall

Severe Tropical Cyclone Ula

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Tropical Cyclone Ula has formed in the southern Pacific, about 300 miles east-northeast of Pago Pago, American Samoa. Winds are estimated at 45kts according to JTWC. Ula has intense central convection, flanked by impressive banding features. The cyclone is currently heading southwards on the west side of a ridge to the east.

The cyclone is poised to strengthen, perhaps rapidly. Shear is low, and Ula is experiencing good, radial outflow. Based on Ula's well organised convective pattern, I'd say it won't be long before Ula is a hurricane strength system, especially as an eye feature appears to be emerging already.

The southward track will continue at first, but Ula is expected to be then steered by a building ridge to the south, which will drive the cyclone to the west. In 4 to 5 days time, Ula should head southwest as it reaches the western periphery of the ridge.

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Ula has rapidly strengthened, and winds are up to 90kts, a cat 2 on the SS scale. The cyclone has developed a small eye, embedded in the small, circular central dense overcast. Further quick strengthening is expected, and I think a cat 4 peak on the SS scale is possible.

20151231.2252.goes15.x.vis1km_high.06PUL

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Ula did not strengthen beyond 90kts as shear rose and weakened the cyclone. Since, Ula has had a second peak of winds at 90kts, and has once more weakened slightly to 85kts. The cyclone will weaken slowly over the coming days as shear slowly increases once more. The track forecast is pretty interesting, with a sessation in poleward movement and a track west favoured. By day 5, Ula should be a very weak system if current forecasts verify, however.

 

sh0616-1.thumb.gif.ba8ae9cfd106713ac3ec0

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Ula is still alive, currently at 45kts and moving northwest after it's southwestward dip. Convection largely vanished over the system yesterday, as dry air and strong shear eroded Ula. Convection has returned over Ula today as the cyclone remains over warm water and has moved into an area of reduced shear. Ula is forecast to slip southwest again in a few days, which will weaken the system again in a few days.

 

sh0616-2.thumb.gif.7e0fdc275a9a9184550a1

 

 

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10 day old Ula continues to restrengthen. Winds are up to 55kts. Ula is now forecast to become a hurricane strength system again before recurving southeast and ultimately becoming extratropical.

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Against all forecasts, Ula has strengthened significantly, and winds are back up at 80kts. The small system has regained a well developed eye. JTWC now forecast a new peak intensity of 110kts in the next 36hrs. 5 days ago, Ula was forecast to be a weakening 35kt system at this point, so the environment has certainly changed in the area.

 

20160108.2100.goes15.x.vis1km_high.06PUL

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For the third time, long lived Ula has reached an intensity of 90kts, cat 2 on the SS scale. The tiny cyclone maintains a fairly large but quite well defined eye this morning. Some additional intensification is expected in the next 24hrs before Ula recurves southeast into cooler waters and higher shear, inducing extratropical transition.

 

Interesting track:

sh0616-3.thumb.gif.aadd14ac35041fa008765

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Ula has become a category 4 on the SS scale, with winds of 115kts. This makes it even more unbelievable that forecasts called for Ula to dissipate after it started properly weakening first time. 

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Ula passing east of New Caledonia with 115kt winds:

 

20160110.1200.goes15.x.ir1km_bw.06PULA.1

It's lucky that a cyclone has intense as Ula has largely avoided the most populated areas on it's twisty track.

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13 day old Ula is now slipping southwards out of the tropics and will accelerate southeastwards whilst completing extratropical transition tomorrow. Winds are down to 65kts currently, and further weakening will occur as Ula transitions, but it will still be a fairly potent extratropical storm. Looks like Ula will hold on long enough as a tropical system to make it 2 weeks old. Interesting storm to track with the very unpredictable intensity!

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It was fun watching little Ula meander across the Pacific, until she strengthened and affected some of the islands that is.  Her extratropical remnants are feeding some moisture down to the North Island of NZ at the moment.

 

Next one to watch is the larger TD08F which is expected to form in the next couple of days and affect the Cook Islands - image copied from Metservice NZ:

Cyclones.thumb.jpg.5de2c2d94384b97bca540

http://www.metservice.com/warnings/tropical-cyclone-activity

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