Tropical Cyclone Joni

[Somerset Squall]

Invest 99P has become better organised overnight, with deep convection developing over a well defined circulation, and convective banding wrapping around this circulation. Therefore, the system now qualifies as a tropical cyclone, 20P, with an inital intensity of 35kts.

20P is located in the southeast Pacific, quite far to the east for a tropical system. The storm is located 100 miles east of Rarotonga, around 158W, 21S. This CIMSS image shows how far east the system is:

To the far left of the image is New Caledonia, which is several hundred miles east of Australia. An this system is over a thousand miles east of New Caledonia, so it gives you an idea how far out to sea it is.

Favourable conditions of low shear, radial outflow and high ocean heat content should allow 20P to intensify over the coming 24hrs. The storm is tracking southwards along the western periphery of a low level ridge east of the system, which should ensure this motion over the coming days. This means in a around 24hrs 20P will reach colder waters if it doesn't manage to turn west. JTWC are calling for dissipation over colder waters in around 36hrs time.

20P is currently bringing very heavy rainfall to Rarotonga. These rains will hopefully subside as 20P moves south.

Edited March 11, 2009 by Ross B

[Cookie]

[Somerset Squall]

Thanks for the images Cookie.

20P has continued to get better organised this afternoon, and has been upgraded to Tropical Cyclone Joni. The storm has good banding features and solid central convection. Joni has the opportunity to strengthen a little before moving over colder waters in around 24hrs time on the southward track.

[Cookie]

joni

[Cookie]

55 knots

[Somerset Squall]

Joni has rapidly intensified to 55kts this evening. Banding is excellent and a good central dense overcast feature has formed. Radial outflow, low shear and warm waters has facilitated this rapid strengthening. However, time is running out for Joni to intensify, as cooler waters are about 12hrs away. In addition, outflow is expected to become more restricted which will cause steady weakening as dry, subsiding air supresses convection. JTWC expect Joni to dissipate over cold waters in 2 days.

[kold weather]

Mind you Joni is already a good deal stronger then was expected by the forecasting agencies so it may last a little longer then expected by them right now. As mentioned before Joni has a really pretty impressive circulation at the moment and earlier microwave suggested strong banding in the southern quadrant, to the point where even a weak eyewall type feature was developing, though I've not seen seen recent enough imagery to see if this is still the case.

Convective bursting is still occuring at the moment and so we should be seeing a peak and then soon after a steady weakening phase kicks in around 6-18hrs time kick in.

Edited March 11, 2009 by kold weather

[J07]

I certainly was not expecting to see a TC out that far.

So far this season NC and the Solomons have been pretty lucky, barring brief flirtation or two. And the main story of the tropical season in terms of weather itself has to date been the heavy rain in Fiji around Christmas, which IIRC was due to the SPCZ, not a cyclone.

[Cookie]

Storm Warning 008 ISSUED FROM RSMC NADI Mar 12/0706 UTC 2009 UTC.

Tropical Cyclone JONI 11F centre [985hPa] CATEGORY 2 was located near

23 decimal 2 South 158 decimal 7 West at 120600 UTC.

Position Poor.

Repeat position 23.2S 158.7W at 120600 UTC.

Cyclone moving south at about 08 knots.

Expect sustained winds of 50 knots close to the centre.

Expect winds over 48 knots within 20 nautical miles of centre.

Expect winds over 33 knots within 150 nautical miles of centre in the

southeastern semicircle and within 60 nautical miles of centre

elsewhere.

Forecast position near 25.4S 158.9W at 121800 UTC.

and near 28.2S 158.9W at 130600 UTC.

[kold weather]

Joni still looking pretty decent, if anything it has strengthened from last night and I'd put it between 60-65kts right now, decent CDO now establised and there is a decent wrapround around the center as well which suggests about the strength I've suggested.

Still would expect it to weaken fairly soon though.

[Somerset Squall]

Still would expect it to weaken fairly soon though.

Indeed, and that process looks like it's begun. Shear is gradually increasing and waters are also cooling as Joni moves south. JTWC have weakened the storm to 50kts, and expected Joni to dissipate shortly after 24hrs. The storm doesn't look as organised as it was earlier with convectional banding decreasing, particularly in the northwestern quadrant, though convection is still persisting over the centre.

[Somerset Squall]

Joni is not giving up that easily. Over the last few hours, Joni has strengthened again, and intensity is currently back up at 55kts. The system's banding features are improving again with a strong feeder band wrapping itself into the eastern quadrant of the storm. Joni is moving into cooler waters, so it can only be said that weakening should resume soon, but this has been said before. Low shear and good outflow is probably cancelling out the cooler waters for now but stronger shear should affect Joni tommorrow.

[Cookie]

thanks for the updates guys

[Cookie]

newer image

[Somerset Squall]

Joni has rapidly weakened today, and intensity has decreased to 35kts. You can see by latest satellite imagery that the LLC has become distorted and ill defined, and convection is rapidly decreasing in coverage. Shear has been analysed to be at around 30-40kts, which is far too high for a tropical cyclone to sustain itself. Additionally, Joni has accelerated south into much colder waters. JTWC have issued their final alert on Joni as they expect full dissipation within the next 24hrs.

[Cookie]

thanks for the updates, she got mangled fast!