SIO: LORNA - Post-Tropical

[Nancy Smar]

SH, 90, 2019042018, , BEST, 0, 50S, 790E, 15, 0, DB, 0, , 0, 0, 0, 0, 0, 0, 0, 0, 0, , 0, , 0, 0, INVEST, ,

[Nancy Smar]

East of Diego Garcia :
Benefiting from conducive environmental conditions aloft and from a good low-level convergence, a clockwise circulation should emerge within the Eastern NET branch by the end of the week-end. From Tuesday, the strengthening upper divergence should allow the development of the system. The available guidance is in good agreement to forecast a moderate cyclogenesis risk for the second half of next week.
For the next five days, the risk of formation of a moderate tropical storm becomes low Wednesday then moderate from Thursday east of Diego Garcia.

[TorSkk]

Upgraded to Cyclone Lorna. The 2018-19 season is now the most active on record

[Sciencerocks]

26/0530 UTC 11.3S 87.1E T3.5/3.5 LORNA

[Sciencerocks]

WTXS32 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 25S (LORNA) WARNING NR 019//
RMKS/
1. TROPICAL CYCLONE 25S (LORNA) WARNING NR 019
01 ACTIVE TROPICAL CYCLONE IN SOUTHIO
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
280000Z --- NEAR 15.8S 89.0E
MOVEMENT PAST SIX HOURS - 180 DEGREES AT 08 KTS
POSITION ACCURATE TO WITHIN 025 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 060 KT, GUSTS 075 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 050 KT WINDS - 070 NM NORTHEAST QUADRANT
065 NM SOUTHEAST QUADRANT
050 NM SOUTHWEST QUADRANT
045 NM NORTHWEST QUADRANT
RADIUS OF 034 KT WINDS - 130 NM NORTHEAST QUADRANT
125 NM SOUTHEAST QUADRANT
100 NM SOUTHWEST QUADRANT
095 NM NORTHWEST QUADRANT
REPEAT POSIT: 15.8S 89.0E
---
FORECASTS:
12 HRS, VALID AT:
281200Z --- 17.7S 89.2E
MAX SUSTAINED WINDS - 055 KT, GUSTS 070 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 050 KT WINDS - 070 NM NORTHEAST QUADRANT
070 NM SOUTHEAST QUADRANT
040 NM SOUTHWEST QUADRANT
030 NM NORTHWEST QUADRANT
RADIUS OF 034 KT WINDS - 170 NM NORTHEAST QUADRANT
240 NM SOUTHEAST QUADRANT
200 NM SOUTHWEST QUADRANT
080 NM NORTHWEST QUADRANT
VECTOR TO 24 HR POSIT: 190 DEG/ 09 KTS
---
24 HRS, VALID AT:
290000Z --- 19.4S 88.9E
MAX SUSTAINED WINDS - 050 KT, GUSTS 065 KT
WIND RADII VALID OVER OPEN WATER ONLY
RADIUS OF 050 KT WINDS - 040 NM NORTHEAST QUADRANT
090 NM SOUTHEAST QUADRANT
060 NM SOUTHWEST QUADRANT
020 NM NORTHWEST QUADRANT
RADIUS OF 034 KT WINDS - 240 NM NORTHEAST QUADRANT
300 NM SOUTHEAST QUADRANT
230 NM SOUTHWEST QUADRANT
090 NM NORTHWEST QUADRANT
VECTOR TO 36 HR POSIT: 190 DEG/ 09 KTS
---
36 HRS, VALID AT:
291200Z --- 21.1S 88.5E
MAX SUSTAINED WINDS - 040 KT, GUSTS 050 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
RADIUS OF 034 KT WINDS - 220 NM NORTHEAST QUADRANT
290 NM SOUTHEAST QUADRANT
190 NM SOUTHWEST QUADRANT
070 NM NORTHWEST QUADRANT
VECTOR TO 48 HR POSIT: 175 DEG/ 10 KTS
---
EXTENDED OUTLOOK:
48 HRS, VALID AT:
300000Z --- 23.1S 88.6E
MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
---
REMARKS:
280300Z POSITION NEAR 16.3S 89.0E.
TROPICAL CYCLONE (TC) 25S (LORNA), LOCATED APPROXIMATELY 507 NM WEST-
SOUTHWEST OF COCOS ISLAND, AUSTRALIA, HAS TRACKED SOUTHWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS THE SYSTEM CONTINUED TO DETERIORATE AS
EVIDENCED BY ELONGATION ALONG THE SOUTHERN FLANK AND WARMING CENTRAL
CLOUD TOPS. HOWEVER, RAIN BANDS REMAIN TIGHTLY WRAPPED INTO THE LOW
LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS EXTRAPOLATED
FROM DEFINED LLCS IN THE 272235Z AMSU AND 272035Z SSMI 37GHZ
MICROWAVE IMAGES. THE INITIAL INTENSITY IS HELD SLIGHTLY LOWER THAN
DVORAK ESTIMATES OF T4.0/65KTS TO REFLECT THE CONVECTIVE DECAY. UPPER
LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA OF HIGH (25 KNOTS
AND INCREASING) VERTICAL WIND SHEAR (VWS). HOWEVER, A STRONG POLEWARD
OUTFLOW CONTINUES TO PROVIDE VENTILATION TO THE ASSOCIATED
CONVECTION. ALONG TRACK SEA SURFACE TEMPERATURES ARE BECOMING LESS
CONDUCIVE AT 27C. TC 25S WILL CONTINUE TO TRACK ALONG THE WESTERN
PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST.
AFTER TAU 12, THE STR IS EXPECTED TO BUILD SLIGHTLY AND STEER THE
CYCLONE ON A MORE SOUTH-SOUTHWESTWARD TRACK. INCREASING VWS AND
COOLING SSTS WILL TRIGGER A GRADUAL WEAKENING PHASE, LEADING TO
DISSIPATION BY TAU 48. NUMERICAL MODELS ARE IN GOOD AGREEMENT,
LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 280000Z IS 27 FEET. NEXT WARNINGS AT
280900Z, 281500Z, 282100Z AND 290300Z.//
NNNN

[TorSkk]

RSMC / TROPICAL CYCLONE CENTER / LA REUNION
TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN)

1.A POST-TROPICAL DEPRESSION 15 (EX-LORNA)

OVER THE LAST 6 HOURS, CLOUD PATTERN HAS DETERIORATED DUE TO STRONG
INCREASING WESTERLY VERTICAL WINDSHEAR (ANALYSED AT 40 KT BY THE CIMSS
AT 09Z) WITH A CENTER COMPLETLY EXPOSED NORTH-WEST TO THE DEEP
CONVECTION.
DURING THE NEXT FEW DAYS, LORNA SHOULD KEEP ON ITS SOUTHWARD TRACK,
NEAR 90°EAST, STEERING BY THE WESTERN SIDE OF THE MID LEVEL RIDGE. FROM
TUESDAY, A MID LEVEL RIDGE LOCATED SOUTH OF THE SYSTEM THAT LIMITED A
FASTER EVACUATION TO THE SOUTH IS EXPECTED TO MOVE EASTWARD WITH THE
ARRIVAL OF A DEEP UPPER LEVEL TROUGH COMING FROM THE SOUTH-WEST. SO
LORNA SHOULD ACCELERATE TOWARDS THE SOUTHEAST AHEAD THE TROUGH.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN UNFAVORABLE. THE
NORTH-WESTERLY TO WESTERLY VERTICAL WINDSHEAR IS STRONG INDUCING DRY
AIR INTRUSIONS IN MID TROPOSPHERE. THE SYSTEM IS FORECAT TO FILL UP MORE
CLEARLY FROM TUESDAY.