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Southern Hemisphere Tropical Cyclone Discussion


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Didn't see a thread so I figured I'd start one.

 

Tropical Cyclone Bansi (05S) is currently located in the SW Indian Ocean a ways north of La Reunion. Bansi is assessed by JTWC as being of an intensity of 130 kt (1 min) and forecast to strengthen as high as 150 kt, solid category five equivalent intensity. The storm will likely pass between Mauritius and Rodrigues in the next couple of days.

 

LATEST.jpg

 

sh0515.gif

 

Not sure how much attention this thread will attract, but it might help some of us get that tropical cyclone fix during the northern hemisphere offseason.

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ADT was having some issues locating the eye of Bansi earlier (as seen with the waviness of the adjusted T values), but seems to be sorted out for now. Raw Ts with version 8.2.1 up to 7.0 now.

 

05S.GIF

 

05SP.GIF

 

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.2.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 12 JAN 2015 Time : 223000 UTC
Lat : 17:27:35 S Lon : 57:12:32 E


CI# /Pressure/ Vmax
5.8 / 950.0mb/109.8kt



Final T# Adj T# Raw T#
5.8 6.7 7.0

Estimated radius of max. wind based on IR : 16 km

Center Temp : +12.9C Cloud Region Temp : -77.9C

Scene Type : EYE

Positioning Method : RING/SPIRAL COMBINATION

Ocean Basin : INDIAN
Dvorak CI > MSLP Conversion Used : PACIFIC

Tno/CI Rules : Constraint Limits : 1.3T/6hr
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : 133km
- Environmental MSLP : 1010mb

Satellite Name : MET7
Satellite Viewing Angle : 20.4 degrees

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Bansi is likely near peak intensity. The central dense overcast has become more asymmetric over the past few hours despite persistent convection <-80C. As strong as the cyclone is now, I think it would've had the potential to go even higher if it weren't for an anticyclone positioned offshore the southeastern coast of Africa. This feature appears to be imparting westerly shear on the system and perhaps advecting some drier air into the circulation.

 

Either way, definitely a beauty.

 

Wty0ila.gif

x3OzQXm.gif

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Yep, agree Bansi has peaked (although it's quite a bit easier to tell now visiting this thread over 12 hours later). Thinking the shear TA13 mentioned helped get a bit of dry air into the core. MW shows a good deal of the west side of the storm missing and also alludes to the possibility of an eyewall replacement cycle. JTWC has the storm getting back up to 140 kt in their latest forecast, but that seems unlikely to me based on the latest microwave passes and with dry air still lurking about.

 

20150113.1242.f16.x.91h.05SBANSI.130kts-

 

20150113.1449.f17.x.vapor.05SBANSI.130kt

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Bansi's massive eye is clearing out now. The now much larger tropical cyclone could be headed for Rodrigues in 36 hours or so.

 

2015SH05_4KMIRIMG_201501142230.GIF

The 18z GFS forecasts Bansi to undergo rapid intensification over the next day, reaching a minimum pressure of 910mb by 12z Friday. The 12z ECMWF is a bit more reserved and slower, showing a peak of 927mb by 12z Saturday.

 

eEtWUDl.png

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Rapid intensification would be a curious occurance to say the least considering the current structure. I could see the storm possibly go annular if it drops some of the banding, but I'm a little skeptical about rapid intensification prospects. Crazier things have happened though I suppose.

 

Here's another VIIRS night visible image.

 

2015SH05_SRSNPPTN_201501142116.png

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I see JTWC is all gung-ho on intensity again, but I'm still skeptical category 5 can be reached a second time. Convection has warmed some during the day there (to be expected to some extent), but the convective pattern seems a little more disorganized than one would expect to occur with direct solar heating. Microwave passes have been a little thin lately, but both an AMSU and an AMSUB pass (the low res ones) within the past few hours suggest that part of the western eyewall may be thin or even missing.

 

1118Z AMSU pass:

 

2015SH05_AMSUSR89_201501151118.GIF

 

1221Z AMSUB pass:

 

20150115.1221.noaa18.x.89.05SBANSI.120kt

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La Reunion, which is the official RSMC for the South-West Indian Ocean, assessed 10-minute sustained winds of 130kt or 1-minute sustained winds of 150kt at 6z last night, making Eunice the strongest cyclone on record in the basin. This surpasses the previous record of 125kt 10-minute winds, or 145kt 1-minute winds, held by 2004's Cyclone Gafilo.

 

An impressive feat in the wake of a weak upward MJO signal and a convectively-suppressed kelvin wave.

 

Based on microwave imagery, Eunice is likely a bit past peak as dry air enters the eastern semicircle of the cyclone.

 

W5hdxMo.jpg

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  • 3 weeks later...
  • 3 weeks later...

Models continue to show the South Pacific becoming very active with tropical cyclones this week. European model shows an intense TC forming in the area E of Vanuatu, with another strong TC developing NW of Australia and threatening their west coast. Also hints at another TC developing NE of Australia and potentially threatening Queensland.

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Yeah, guidance is certainly raising some eyebrows in the southern hemisphere, particularly in the South Pacific near Vanuatu. All the globals are very consistent in developing a very strong system out of 93P, with the GFS developing something historic. Whether or not you believe the bonkers GFS output or not, 93P is developing over the warmest and most heat laden waters in the entire world. Based on all this, I'd say the confidence is fairly high that we could be looking at something quite interesting this coming week, and that's not even outlining the other possible threats wxsmwhrms mentioned above.

 

2015065sst.png

 

2015065.png

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Ha yep, the GFS has been deep below 900 mb with 93P for many consecutive runs now. We should all be skeptical of output like that, but other guidance is forecasting a strong storm too. Looking at the environment, it's not hard to see why either.

 

Speaking of 93P, it might be time for an upgrade based on the latest microwave pass, which clearly shows a low level circulation directly beneath a central convective complex with tops approaching -100*C.

 

20150308.1354.gcomw1.x.89h.93PINVEST.25k

 

2015SH93_4KMIRIMG_201503081532.GIF

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Not getting much publicity but the capital of Vanuatu (Port-Vila) is at risk of taking a direct hit by Pam. 140/150 kt, sub 900 range.

 

The latest forecast track has Pam moving south and then sse, with the eye remaining just east of the islands, but that's not what's happening.  Instead, it continues to track ssw and it appears the eye will hit the capital.

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The latest forecast track has Pam moving south and then sse, with the eye remaining just east of the islands, but that's not what's happening.  Instead, it continues to track ssw and it appears the eye will hit the capital.

 

Appears the western eyewall is going right over them. Well, at least it appears the cloud tops warmed a tad on approach and they are on the slighty weaker side of the storm. Regardless, this is going to be a very severe for those islands.

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 Two southern-most islands are now about to get raked with the stronger eastern eyewall. Appears the capital itself may have just missed the eyewall (though not the eastern end of the island). Given the track and storrm strength, Pam is likely going to be the most damaging cyclone for these islands.

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