Intense Tropical Cyclone Cleo

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Invest 90S has become the third tropical cyclone of the season with intensity at 35kts. Latest warning from JTWC:

TROPICAL CYCLONE (TC) 03S (THREE), LOCATED APPROXIMATELY 570 NM EAST

OF DIEGO GARCIA, HAS TRACKED WESTWARD AT 08 KNOTS OVER THE PAST SIX

HOURS. RECENT ANIMATED INFRARED SATELLITE IMAGERY AND A 062050Z TRMM

IMAGE SHOW IMPROVED CONVECTIVE BANDING WRAPPING INTO A LOW LEVEL

CIRCULATION CENTER. A 062330Z PGTW DVORAK VALUE OF 2.5 AND IMPROVING

STRUCTURE EVIDENT IN THE AFOREMENTIONED TRMM IMAGE INDICATE THAT

MAXIMUM SUSTAINED WIND SPEEDS HAVE INCREASED TO THE 35 KNOT WARNING

INTENSITY THRESHOLD. TC 03S IS TRACKING WESTWARD ALONG THE NORTHERN

PERIPHERY OF A MID-LEVEL SUBTROPICAL STEERING RIDGE TO THE EAST-

SOUTHEAST. AN APPROACHING MIDLATITUDE TROUGH IS EXPECTED TO WEAKEN

THE STEERING RIDGE, INDUCING A POLEWARD STAIRSTEP IN THE STORM TRACK

THROUGH ABOUT TAU 36. THEREAFTER, THE SUBTROPICAL RIDGE WILL BUILD

IN THE WAKE OF THE MIDLATITUDE TROUGH AND TC 03S WILL RESUME A

WESTWARD TRACK. TC 03S IS LOCATED EQUATORWARD OF AN UPPER-LEVEL

RIDGE AXIS, IN AN AREA OF LOW TO MODERATE EASTERLY VERTICAL WIND

SHEAR AND GOODD POLEWARD OUTFLOW. THE SYSTEM WILL INTENSIFY OVER

THE NEXT 72 HOURS AS THESE FAVORABLE UPPER LEVEL CONDITIONS PERSIST.

THEREAFTER, THE INTENSITY IS EXPECTED TO LEVEL OFF AS ALONG TRACK

OCEAN HEAT CONTENT DECREASES AND VERTICAL WIND SHEAR INCREASES

SLIGHTLY. THE AVAILABLE NUMERICAL MODEL GUIDANCE IS IN FAIR

AGREEMENT WITH THIS STORM TRACK FORECAST, WITH ALL MODELS

FORECASTING A STEADY WESTWARD TRACK. THIS WARNING SUPERSEDES AND

CANCELS REF A, NAVMARFCSTCEN 061121Z DEC 09 TROPICAL CYCLONE

FORMATION ALERT (WTXS21 PGTW 061130). MAXIMUM SIGNIFICANT WAVE

HEIGHT AT 070000Z IS 11 FEET. NEXT WARNINGS AT 071500Z AND 080300Z.//

NNNN

[Cookie]

[Somerset Squall]

03S has intensified through today, and is now named Cleo, with intensity having risen to 45kts. Cleo is developing in a favourable environment of low shear, warm sea temperatures and good outflow. These conditions will allow Cleo to strengthen further and MeteoFrance and JTWC seem both keen on at least bringing Cleo to cat 1 status, if not higher. Cleo already has an impressive central dense overcast with spiral banding- so all we need to look for now is the eye. In about 72hrs, shear is expected to increase, but only modestly, which will be enough to cause some weakening or a plateaux in intensity gain. Westwards heading should continue over the next few days with a subtropical ridge to the south being the primary steering influence. Track speeds will be quite quick initially, but the ridge is expected to slowly weaken which will slow Cleo down.

It is uncertain whether Cleo will affect land as yet but it should pass well south of Diego Garcia.

Image from MeteoFrance showing Cleo:

Edited December 7, 2009 by Somerset Squall

[Somerset Squall]

Cleo has literally gone nuts over the last 24hrs. Intensity increased to 55kts in the early hours, but then Cleo developed the dreaded pinhole eye today. Intensity is now 105kts, and pressure did fall to 927mb earlier today but has since risen a little (pressure fluctuations are common in intense tropical cyclones). That's an intensity gain of 60kts in 24hrs, which is nothing short of amazing!

Cleo has the potential to strengthen further over the next 36hrs, and a high end cat 4 seems likely, or even cat 5 can't be ruled out. Cleo has a very impressive structure with a well defined eye, and is over hot waters of around 30C. Shear is also low and outflow is excellent in all directions. After 36hrs, shear increases a little on the west-southwest track and water temps taper off a little. At this stage, Cleo is likely to begin to weaken.

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JTWC has upped Cleo's intensity to 115kts, making her a cat 4.

[Cookie]

another mental intensification again go Cleo

[Cookie]

starting to go down now

[Somerset Squall]

Indeed Cookie. Cleo is moving over cooler waters and moderate shear. Intensity has been reduced to 90kts. Cleo sill maintains a CDO feature for now, but the well defined eye of earlier is gone. A trough will eventually break down the subtropical ridge to the south, and a re-curve south and then southeastwards is favoured beyond 72hrs. This will cause extratropical transition to begin as the sea temps shelve off sharply to the south.

[Cookie]

down to a tropical storm

[Somerset Squall]

Cleo has been declared a remnant low. It's rapid demise in the final hours was due to strong shear and dry air which has stripped the LLC of convection. Due to the continuing hostility to the environment, redevelopment is unlikely.

Still, an interesting cyclone, particularly for it's rapid intensification. And a good start to the south indian ocean season to already have two cat 4's before mid December.

[Somerset Squall]

Cleo has made a comeback this morning, with deep convection persisting over the still well defined LLC. Cleo's second life should be shorter than the first, as the cyclone is moving towards cooler waters on a southerly track around the western periphery of a subtropical ridge positioned to the east. After 24hrs, Cleo is also expected to move into higher shear. These two factors suggest that extratropical transition to a weak baroclinic system will occur. However, for the next 24hrs, conditions are favourable which is why Cleo has respawned in the first place. Shear has lessened over the last 48hrs, and poleward outflow is good which has allowed the persistant convection to form. JTWC forecast that Cleo should strengthen today to a 35kt system, though with the outflow and low shear I think Cleo could make it to 40kts before the conditions deteriorate again.

It's worth noting that Cleo has travelled quite far west as a remnant low and therefore is quite close to Mauritius and La Reunion. Cleo could bring heavy rains to these islands as it passes to the east.

Satellite image showing Cleo reborn (a few hundred miles east of Madagascar):

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Cleo has not been holding on to deep convection for long enough periods to be classified as a TC anymore. A massive blow up of convection has occured in the last few hours, and a few hours before that the weakening LLC of Cleo had little convection attached to it. It seems that Cleo has already entered high shear and cooler waters which is disrupting the convective development. Cleo's remnants could still bring heavy rains to Mauritius before it pulls away to the southeast as it rounds the western periphery of the subtropical ridge to the east. Re-generation is not expected, unless this recent convective activity persists.