SIO: CHERONO (07R/18S) - Tropical Depression

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WTIO30 FMEE 201241


RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE TECHNICAL BULLETIN (SOUTH-WEST INDIAN OCEAN)

0.A WARNING NUMBER : 22/7/20102011
1.A TROPICAL DEPRESSION 7 (EX-CHERONO)

2.A POSITION 2011/03/20 AT 1200 UTC :
WITHIN 20 NM RADIUS OF POINT 21.7S / 60.5E
(TWENTY ONE DECIMAL SEVEN DEGREES SOUTH AND SIXTY DECIMAL FIVE DEGREES
EAST)
MOVEMENT : WEST-SOUTH-WEST 12 KT

3.A DVORAK ANALYSIS : 2.5/2.5 /D 0.5/12 H
4.A CENTRAL PRESSURE : 997 HPA
5.A MAX AVERAGE WIND SPEED (10 MN) : 30 KT
RADIUS OF MAXIMUM WINDS (RMW) : 40 KM

6.A EXTENSION OF WINDS BY QUADRANTS (KM):
28 KT NE: 075 SE: 330 SO: 330 NO: 055
34 KT NE: SE: 130 SO: 130 NO:

7.A FIRST CLOSED ISOBARE (PRESSURE / AVERAGE DIAM): 1006 HPA / 440 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: DEEP

1.B FORECASTS:
12H: 2011/03/21 00 UTC: 22.9S/57.9E, MAX WIND=040KT , MODERATE TROP.
STORM.
24H: 2011/03/21 12 UTC: 24.2S/55.6E, MAX WIND=040KT , SUBTROPICAL.
36H: 2011/03/22 00 UTC: 25.5S/54.1E, MAX WIND=035KT , SUBTROPICAL.
48H: 2011/03/22 12 UTC: 26.9S/53.5E, MAX WIND=035KT , EXTRATROPICAL.
60H: 2011/03/23 00 UTC: 28.3S/54.6E, MAX WIND=030KT , EXTRATROPICAL.
72H: 2011/03/23 12 UTC: 29.5S/57.6E, MAX WIND=030KT , EXTRATROPICAL.

2.B LONGER-RANGE OUTLOOK:
96H: 24/03/2011 12 UTC: 30.7S/65.5E, MAX WIND=035KT , EXTRATROPICAL.
120H: 25/03/2011 12 UTC: 30.4S/75.9E, MAX WIND=035KT , EXTRATROPICAL.

2.C ADDITIONAL INFORMATIONS:
T=2.5- CI=2.5
VERTICAL WINDSHEAR HAS WEAKENED AND DEEP CONVECTION EXISTS MORE CLOSER TO
THE CENTER WITHIN THE LAST PAST HOURS.
LLCC IS NO MORE EXPOSED SINCE 1030Z BUT 0910Z TRMM MULTISPECTRAL IMAGERY
REVEALED JUST BEFORE A LESS DEFINED LLCC THAN THE PREVIOUS 0414Z F18
IMAGERY.
IT IS THEREFORE UNLIKELY THAT WINDS IN THE NORTHERN SEMI-CIRCHE HAS
ENOUGH STRENGHTENED TO ALLOW THE SYSTEM HAVING REACH BACK MODERATE STORM
STAGE.
DEEP CONVECTIVE ACTIVITY HOWEVER ONLY EXISTS IN THE SOUTHEASTERN
SEMI-CIRCLE. CONVECTION KEEPS ON FLARING UP , WELL SUSTAINED BY THE VERY
FAVOURABLE POLEWARD UPPER LEVEL DIVERGENCE.
STRUCTURE IS ASYMETRIC WITH STRONGESTS WINDS EXTENDING FAR IN THE SOUTH
DUE TO THE GRADIENT EFFECT WITH THE SUBTROPICAL HIGH PRESSURES.
VERTICAL WINDHSEAR IS EXPECTED TO STRENGTHEN AGAIN GRADUALLY ALOFT AS THE
SYSTEM IS APPROCHING AN UPPER LEVEL TROUGH LOCATED TO THE SOUTHWEST.
SEVERAL NWP MODELS (AS ECMWF AND FRENCH MODEL ARPEGE) CLEARLY SUGGEST AN
INTERACTION BETWEEN EX-CHERONO AND THE UPPER LEVEL TROUGH MONDAY AND
TUESDAY ...THERMODYNAMICAL STRUCTURE OF THE SYSTEM COULD EVOLVE TOWARDS
AN HYBRID FORM ...MEANS SUBTROPICAL FORM (SUGGESTED BY PHASIS DIAGRAM
FROM GFS).
THIS SCENARIO APPEAR NOW LIKELY AND IS REFLECTED IN THE CURRENT INTENSITY
FORECAST.
THE CURRENT TRACK TOWARDS THE WEST-SOUTH-WEST SHOULD MAINTAIN WITHIN THE
NEXT 24 TO 36 HOURS. BEYOND, THE MORE REALISTIC FORECAST REMAINS
RECURVATURE OF THE TRACK SOUTHWARDS AND THEN SOUTHEASTWARDS IN RELATION
WITH A GAP IN THE SUBTROPICAL HIGH PRESSURE.

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WTIO30 FMEE 210007
RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE TECHNICAL BULLETIN (SOUTH-WEST INDIAN OCEAN)
0.A WARNING NUMBER : 24/7/20102011
1.A TROPICAL DEPRESSION 7 (EX-CHERONO)
2.A POSITION 2011/03/21 AT 0000 UTC :
WITHIN 30 NM RADIUS OF POINT 22.8S / 58.7E
(TWENTY TWO DECIMAL EIGHT DEGREES SOUTH AND FIFTY EIGHT DECIMAL SEVEN
DEGREES EAST)
MOVEMENT : WEST-SOUTH-WEST 12 KT
3.A DVORAK ANALYSIS : 2.0/2.5 /S 0.5/6 H
4.A CENTRAL PRESSURE : 997 HPA
5.A MAX AVERAGE WIND SPEED (10 MN) : 30 KT
RADIUS OF MAXIMUM WINDS (RMW) : 45 KM
6.A EXTENSION OF WINDS BY QUADRANTS (KM):
28 KT NE: 055 SE: 400 SO: 370 NO: 090
34 KT NE: SE: 150 SO: 150 NO:
7.A FIRST CLOSED ISOBARE (PRESSURE / AVERAGE DIAM): 1009 HPA / 400 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM
1.B FORECASTS:
12H: 2011/03/21 12 UTC: 23.8S/56.3E, MAX WIND=040KT, SUBTROPICAL.
24H: 2011/03/22 00 UTC: 25.0S/54.7E, MAX WIND=040KT, SUBTROPICAL.
36H: 2011/03/22 12 UTC: 26.2S/54.1E, MAX WIND=040KT, SUBTROPICAL.
48H: 2011/03/23 00 UTC: 28.0S/54.4E, MAX WIND=030KT, BECOMING
EXTRATROPICAL.
60H: 2011/03/23 12 UTC: 29.3S/57.2E, MAX WIND=030KT, BECOMING
EXTRATROPICAL.
72H: 2011/03/24 00 UTC: 30.2S/60.8E, MAX WIND=040KT, EXTRATROPICAL.
2.B LONGER-RANGE OUTLOOK:
96H: 25/03/2011 00 UTC: 31.2S/70.2E, MAX WIND=040KT, EXTRATROPICAL.
120H: 26/03/2011 00 UTC: 33.3S/81.3E, MAX WIND=025KT, EXTRATROPICAL.
2.C ADDITIONAL INFORMATIONS:
T=2.0 CI=2.5
CONVECTVE ACTIVITY HAS LESSENING FOR THE LAST 6 HOURS.
CENTER HAS BEEN LOCATED BY EXTRAPOLATION OF THE AVHRR-NOAA18 AT 21.19Z.
LOW LEVEL CENTER KEEPS ON TRACKING WEST-SOUTH-WESTWARD.
UPPER LEVELS VERTICAL WIND SHEAR IS STRENGTHENING AHEAD A TROUGH WEST OF
THE SYSTEM.
THE WIND PATTERN OF THE REMNANT LOW REMAINS ASYMETRIC WITH STRONGER WINDS
IN THE SOUTHERN SEMI-CICRLE IN RELATION WITH THE GRADIENT EFFECT WITH
THE SUBTROPICAL HIGH PRESSURE (CF ASCAT DATA AT 18.18Z).
WITHIN THE NEXT 24 TO 36 HOURS, NWP MODELS SUGGEST THAT SYSTEM SHOULD
ENTER IN PHASE WTH THE APPROACHING UPPER LEVEL TROUGH. EX-CHERONO SHOULD
EVOLVE IN A SUBTROPICAL STRUCTURE (CF PHASIS DIAGRAM FROM GFS).
SURFACE WIND SHOULD STENGTHEN.
BEYOND J+3 (WEDNESDAY) SYSTEM SHOULD BEGIN ITS EXTRATROPICAL TRANSITION.
SYSTEM IS EXPECTED TO KEEP ON TRACKING WEST-SOUTHWESTWARD TO
SOUTH-WESTWARD DURING THE NEXT 36 HOURS. BEYOND, IT SHOULD SLOW DONWN AND
THE RECURVE SOUTH-EAST AND THEN EASTWARD.

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ZCZC 439
WTIO30 FMEE 210641
RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE TECHNICAL BULLETIN (SOUTH-WEST INDIAN OCEAN)
0.A WARNING NUMBER : 25/7/20102011
1.A TROPICAL DEPRESSION 7 (EX-CHERONO)
2.A POSITION 2011/03/21 AT 0600 UTC :
WITHIN 20 NM RADIUS OF POINT 23.1S / 58.1E
(TWENTY THREE DECIMAL ONE DEGREES SOUTH AND FIFTY EIGHT DECIMAL ONE
DEGREES EAST)
MOVEMENT : WEST-SOUTH-WEST 8 KT
3.A DVORAK ANALYSIS : 2.5/2.5 /D 0.5/6 H
4.A CENTRAL PRESSURE : 997 HPA
5.A MAX AVERAGE WIND SPEED (10 MN) : 30 KT
RADIUS OF MAXIMUM WINDS (RMW) : 45 KM
6.A EXTENSION OF WINDS BY QUADRANTS (KM):
28 KT NE: 055 SE: 400 SO: 370 NO: 090
34 KT NE: SE: 150 SO: 150 NO:
7.A FIRST CLOSED ISOBARE (PRESSURE / AVERAGE DIAM): 1009 HPA / 400 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: MEDIUM
1.B FORECASTS:
12H: 2011/03/21 18 UTC: 24.8S/55.8E, MAX WIND=040KT, SUBTROPICAL.
24H: 2011/03/22 06 UTC: 26.3S/55.2E, MAX WIND=040KT, SUBTROPICAL.
36H: 2011/03/22 18 UTC: 28.0S/56.9E, MAX WIND=040KT, SUBTROPICAL.
48H: 2011/03/23 06 UTC: 29.3S/59.8E, MAX WIND=040KT, BECOMING
EXTRATROPICAL.
60H: 2011/03/23 18 UTC: 30.1S/63.9E, MAX WIND=035KT, EXTRATROPICAL.
72H: 2011/03/24 06 UTC: 30.5S/69.1E, MAX WIND=035KT, EXTRATROPICAL.
2.B LONGER-RANGE OUTLOOK:
96H: 25/03/2011 06 UTC: 32.6S/81.4E, MAX WIND=035KT, EXTRATROPICAL.
120H: 26/03/2011 06 UTC: 31.6S/88.0E, MAX WIND=030KT, EXTRATROPICAL.
2.C ADDITIONAL INFORMATIONS:
T=2.5 CI=2.5
CONVECTION IS VERY FLUCTUATING AND REMAINS CONFINED IN THE SOUTHERN PART
OF THE SYSTEM THAT IS STILL UNDERGOING A NORTHWESTERLY WINDSHEAR. LLCC IS
WELL VISIBLE ON LATEST CC SATELLITE IMAGERY AND CONTINUES TO TRACK
WEST-SOUTHWESTWARD. THE WINDS STRUCTURE REMAINS ASYMMETRIC WITH STRONGER
WINDS IN THE
SOUTHERN SEMI-CIRCLE DUE TO GRADIENT EFFECT WITH THE SUBTROPICAL HIGH
PRESSURES (CF ASCAT DATA AT 20/1818Z).
SYSTEM IS EXPECTED TO KEEP ON TRACKING WEST-SOUTHWESTWARD TO
SOUTH-WESTWARD DURING THE NEXT 12 HOURS. BEYOND, IT SHOULD SLOW DOWN AND
RECURVE SOUTH-EASTWARD AND THEN EASTWARD.
VERTICAL WINDSHEAR REMAINS STRONG AHEAD OF UPPER LEVEL TROUGH EXISTING
WEST OF THE SYSTEM. WITHIN THE NEXT 24 HOURS, THE SYSTEM SHOULD ENTER IN
PHASE WTH THE APPROACHING UPPER LEVEL TROUGH. EX-CHERONO SHOULD EVOLVE IN
A SUBTROPICAL STRUCTURE (CF PHASIS DIAGRAM FROM GFS). SURFACE WINDS
MIGHT STRENGTH
EN SOME STILL DUE TO GRADIENT EFFECT IN THE SOUTHERN PART OF THE SYSTEM.
BEYOND WEDNESDAY, SYSTEM SHOULD BEGIN ITS EXTRATROPICAL TRANSITION IN THE
SOUTH LATITUDES WESTERLY CIRCULATION .
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