Severe Tropical Cyclone Bune

[Somerset Squall]

After a month of silence from the South Pacific, invest 99P has become the nineteenth tropical cyclone this season for the Southern Hemisphere. Intensity is 35kts. 19P is currently in a low shear environment, with waters around 29C beneath the system. These conditions won't last too long however. 19P will head southwestwards and begin interacting with an advancing trough to the west. The trough will increase shear over 19P in about 36hrs time, and at the same time will force the cyclone southwards over cooler water. These two factors will induce extratropical transition. Until then, 19P should intensify. 19P should not affect land.

[onlyME]

Looking good and closing to hurricane strength

Advisory

Tropical cyclone (tc) 19p (bune), located approximately 260 nmsoutheast of Nadi, Fiji, has tracked south-southwestward at 05 knotsover the past six hours. Animated multispectral satellite imageryindicates a consolidating low-level circulation center (LLCC) withdeep convection surrounding the well-defined center. Animated watervapor imagery depicts improving outflow, especially over the westernsemi-Circle. A 240654z ssmis image also supports a consolidatingsystem with tightly-curved banding wrapping into the center andmultiple convective bands over the eastern semi-Circle. The currentposition is based on a 240538z ssmis as well as the 240654z ssmiswith good confidence. The current intensity is based on Dvorakestimates of 45 knots from pgtw, knes and abrf. Tc 19p is trackingslowly southward along the western periphery of the low- to mid-level subtropical ridge and is expected to maintain a generallysouthward track through tau 72. Near tau 72, tc 19p is expected toturn southeastward and to accelerate ahead of an approaching deepmidlatitude shortwave trough. The bulk of the dynamic models supportthis track to include ukmo, GFS, GFDN, ECMWF and WBAR, althoughthere is poor agreement between the models. The NOGAPS model is thesole outlier with an unrealistic westward track through tau 120 thatsomehow steers the system westward despite the deep trough diggingto the system's south. The ukmo and GFDN models have indicated awestward to southwestward track through tau 72 but have beenshifting eastward over the past few runs. This forecast ispositioned on the eastern edge of the aids envelope closer to theGFS and ECMWF solutions, which appear more realistic. Peak intensityhas been increased to 75 knots by tau 72 due to generally favorableconditions to include favorable SST, low to moderate vertical windshear and good outflow. After tau 72, tc 19p is forecast to beginextra-tropical transition (ett) as it interacts with the barocliniczone associated with the aforementioned trough. Tc 19p is expectedto complete ett by tau 120. Maximum significant wave height at240600z is 15 feet. Satellite

[Somerset Squall]

19P has been named Tropical Cyclone Bune with intensity rising quite sharply to 55kts. A banding eye seems to be developing in a well formed central dense overcast feature. Bune should strengthen further over the next 48hrs on the slow south-southwesterly track. Based on the rate of intensification so far, I think the JTWC estimation of a peak of 75kts could well turn out too low.

Thanks for the image Wobbuffet, shows Bune's good organisation well.

[Cookie]

Looking good

[Somerset Squall]

Bune has strengthened further overnight and has become a Severe Tropical Cyclone, with intensity now at 75kts, making Bune a category 1 on the SS scale. Bune has a fairly well developed eye and some strong banding, but convection is limited on the western side of the cyclone due to subsidence. This will limit further intensification but Bune should still reach cat 2 strength on the SS scale. Bune is currently heading southwards but should turn to the southwest soon as a steering ridge builds to the southeast. This southwesterly motion won't last long as an advancing mid-lattitude trough from the west should kick Bune southeastwards at an accelerated speed. This will quickly take Bune over colder water and increase the upper level shear, causing the cyclone to undergo extatropical transition. The system should transform into a pretty potent extratropical storm northeast of New Zealand.

[Somerset Squall]

Subsidence and dry air prevented Bune from strengthening any further, and the storm has now weakened to 65kts. A large dry slot is infiltrating the CDO, and the eye has opened up. However, Bune still has some strong banding on the southern and eastern sides of the LLC. Bune will continue to weaken over progressively cooler water and begin extratropical transition soon.

[onlyME]

Bune got annular look today morning.

[J07]

Suspect Bune will still be classified as a TC at 06Z, 12Z and 18Z. Probably 00Z also, but likely that 06Z will re-classify.

It is looking to make a direct hit on Raoul Island. The DOC workers there have been notified, and warned of sustained winds close to 100km/h and gusts of 150km/h. The centre is likely to be overhead at 12Z! So provided the AWS does not fail we will find out for sure what the central pressure of this TC is, which in this part of the world (very sparse observations) is really rare!

Current warning (00Z today):

TCSTORM WARNING 661

This affects ocean area: SUBTROPIC

Tropical Cyclone BUNE [975hPa] centre was located near 27.4 South 179.1 West at 280000 UTC.

Position Fair.

Repeat position 27.4S 179.1W at 280000 UTC.

Cyclone is moving southeast 12 knots.

Expect sustained winds of 60 knots close to the centre easing to 55 knots by 281200 UTC and then easing to 50 knots by 290000 UTC.

Expect winds over 48 knots within 100 nautical miles of centre.

Expect winds over 33 knots within 220 nautical miles of centre.

Forecast position near 29.7S 177.8W at 281200 UTC

and near 32.1S 176.5W at 290000 UTC.

This warning cancels and replaces warning 654.

Issued at 1:26pm Monday 28 March 2011

[J07]

No longer a TC.

STORM WARNING 689

This affects ocean areas: SUBTROPIC FORTIES and PACIFIC

AT 290000UTC

Low 972hPa, former Cyclone BUNE, near 33S 175W moving southsoutheast 20kt.

1. Within 180 nautical miles of low in sector from southeast through southwest to north: Clockwise 45kt rising to 60kt next 6-12 hours.

2. Outside area 1 and within 180 nautical miles of low in northeast quadrant: Clockwise 55kt.

3. Outside areas 1 and 2 and within 360 nautical miles of low in eastern semicircle: Clockwise 40kt.

4. Outside areas 1 to 3 and within 300 nautical miles of low in western semicircle: Clockwise 40kt.

Storm and gale areas moving with low.

This warning cancels and replaces warning 686.

Issued at 1:24pm Tuesday 29 March 2011

[J07]

A post about Bune passing over the Kermadecs.

http://blog.metservice.com/2011/03/the-eye-of-the-storm/