#3 Postby Extratropical94 » Wed Apr 13, 2011 12:07 pm
WTIO30 FMEE 131248
RSMC / TROPICAL CYCLONE CENTRE / LA REUNION
TROPICAL CYCLONE TECHNICAL BULLETIN (SOUTH-WEST INDIAN OCEAN)
0.A WARNING NUMBER : 1/9/20102011
1.A SUBTROPICAL DEPRESSION 9
2.A POSITION 2011/04/13 AT 1200 UTC :
WITHIN 20 NM RADIUS OF POINT 27.9S / 48.6E
(TWENTY SEVEN DECIMAL NINE DEGREES SOUTH AND FORTY EIGHT DECIMAL SIX
DEGREES EAST)
MOVEMENT : SOUTH-SOUTH-WEST 6 KT
3.A DVORAK ANALYSIS : /D / H
4.A CENTRAL PRESSURE : 1001 HPA
5.A MAX AVERAGE WIND SPEED (10 MN) : 30 KT
RADIUS OF MAXIMUM WINDS (RMW) : NIL
6.A EXTENSION OF WINDS BY QUADRANTS (KM):
28 KT NE: 070 SE: 700 SO: 450 NO: 090
7.A FIRST CLOSED ISOBARE (PRESSURE / AVERAGE DIAM): 1009 HPA / 550 KM
8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION: SHALLOW
1.B FORECASTS:
12H: 2011/04/14 00 UTC: 28.6S/48.1E, MAX WIND=030KT, SUBTROPICAL.
24H: 2011/04/14 12 UTC: 29.9S/46.8E, MAX WIND=030KT, SUBTROPICAL.
36H: 2011/04/15 00 UTC: 31.2S/45.9E, MAX WIND=030KT, SUBTROPICAL.
48H: 2011/04/15 12 UTC: 32.7S/45.9E, MAX WIND=030KT, SUBTROPICAL.
60H: 2011/04/16 00 UTC: 34.7S/47.1E, MAX WIND=030KT, BECOMING
EXTRATROPICAL.
72H: 2011/04/16 12 UTC: 37.7S/49.1E, MAX WIND=035KT, EXTRATROPICAL.
2.B LONGER-RANGE OUTLOOK:
96H: 17/04/2011 12 UTC: 41.8S/57.5E, MAX WIND=035KT, EXTRATROPICAL.
120H: 18/04/2011 12 UTC: 43.8S/69.7E, MAX WIND=030KT, EXTRATROPICAL.
2.C ADDITIONAL INFORMATIONS:
NO DVORAK ANALYSIS.
SATELLITE IMAGERY SHOWS A WELL-DEFINED AND PARTIALLY EXPOSED LOW LEVEL
VORTEX. A CONVECTIVE BAND IS PRESENT IN THE SOUTHERN SEMI-CIRCLE OF THE
SYSTEM AND WRAPS FAIRLY CLOSELY FROM THE CENTRE, BUT DIFFICULTY PERSISTS
AT THIS LOCATION. ASCAT SWATH 0557Z IS NOT CENTERED ON THE SYSTEM, BUT IT
IS VERY LIKELY THAT WINDS STRUCTURE IS ASYMMETRIC WITH A LARGE STRONG WINDS
HALF-RING REACHING 35/40 KT WITH GRADIENT EFFECT FROM 70 TO 250 NM FROM
THE CENTRE, AND WEAKER WINDS AT ABOUT 25/30 KT IN THE NORTHERN
SEMI-CIRCLE THAT JUSTIFY THE SUBTROPICAL DEPRESSION STAGE.
THE SYSTEM STILL EVOLVES IN A BAROCLINIC ENVIRONMENT (COLD UPPER LEVEL
LOW AND LOWER THAN USUAL DYNAMICAL TROPOPAUSE) AND GOOD UPPER LEVEL
DIVERGENCE PRESERVES CONVECTION IN THE SOUTHWESTERN EDGE IN PHASIS WITH A
WEAK VERTICAL WINDSHEAR ON THE TROUGH AXIS.
AVAILABLE NWP MODELS FORECAST THAT THE SYSTEM KEEPS A SOUTH-SOUTHWESTWARD
MOVEMENT FOR THE NEXT 36 HOURS AND BEYOND RECURVES SOUTH-EASTWARD. UNTIL
FRIDAY EVENING, UPPER LEVEL CONDITIONS ARE FAVOURABLE AND THE LOW COULD
A LITTLE DEEPEN. DESPITE COLDER SST (25/26C) TOWARD THE SOUTH, IT IS
POSSIBLE THAT THE SUBTROPICAL SYSTEM TEMPORARILY EVOLVES TO A TROPICAL
STRUCTURE IF CONVECTION INCREASES NEAR THE CENTRE AND PERSISTS. ON
AND AFTER 48/60 HOURS, THE SYSTEM SHOULD BEGIN ITS EXTRA-TROPICALIZATION
IN THE WESTERLY CIRCULATION OF THE MID-LATITUDES.
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