JTWC判定11/06Z升格為Tropical Cyclone 21S，預測將移向西澳西北海岸。

WTXS31 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 21S (TWENTYONE) WARNING NR 001//
REF/A/MSG/JOINT TYPHOON WRNCEN PEARL HARBOR HI/101551ZMAR2020//
AMPN/REF A IS A TROPICAL CYCLONE FORMATION ALERT.//
RMKS/
1. TROPICAL CYCLONE 21S (TWENTYONE) WARNING NR 001   
   01 ACTIVE TROPICAL CYCLONE IN SOUTHIO
   MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
   WIND RADII VALID OVER OPEN WATER ONLY
    ---
   WARNING POSITION:
   110600Z --- NEAR 16.4S 116.9E
     MOVEMENT PAST SIX HOURS - 185 DEGREES AT 09 KTS
     POSITION ACCURATE TO WITHIN 015 NM
     POSITION BASED ON CENTER LOCATED BY SATELLITE
   PRESENT WIND DISTRIBUTION:
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT
                            050 NM SOUTHEAST QUADRANT
                            025 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   REPEAT POSIT: 16.4S 116.9E
    ---
   FORECASTS:
   12 HRS, VALID AT:
   111800Z --- 18.2S 115.9E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 050 NM NORTHEAST QUADRANT
                            060 NM SOUTHEAST QUADRANT
                            020 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 24 HR POSIT: 205 DEG/ 10 KTS
    ---
   24 HRS, VALID AT:
   120600Z --- 19.9S 115.0E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   RADIUS OF 034 KT WINDS - 050 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 36 HR POSIT: 200 DEG/ 10 KTS
    ---
   36 HRS, VALID AT:
   121800Z --- 21.7S 114.3E
   MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
   RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT
                            030 NM SOUTHEAST QUADRANT
                            010 NM SOUTHWEST QUADRANT
                            000 NM NORTHWEST QUADRANT
   VECTOR TO 48 HR POSIT: 195 DEG/ 09 KTS
    ---
   EXTENDED OUTLOOK:
   48 HRS, VALID AT:
   130600Z --- 23.5S 113.7E
   MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
   WIND RADII VALID OVER OPEN WATER ONLY
   DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER
    ---
REMARKS:
110900Z POSITION NEAR 16.9S 116.6E.
11MAR20. TROPICAL CYCLONE (TC) 21S (TWENTYONE), LOCATED APPROXIMATELY
253 NM NORTH-NORTHWEST OF PORT HEDLAND, AUSTRALIA, HAS TRACKED
SOUTHWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) REVEALS A PARTIALLY-EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION LOCATED OVERHEAD.
AN 110616Z AMSR2 89 GHZ MICROWAVE IMAGE DEPICTS A CLEARLY DEFINED
LLCC WITH LIMITED DEEP CONVECTION DIRECTLY OVER THE LLCC AND
EXTENDING TO THE SOUTHEAST. THE INITIAL POSITION IS SET WITH GOOD
CONFIDENCE BASED ON THE AFOREMENTIONED MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 35 KTS IS BASED ON AN 110152Z METOP-C DIRECT ASCAT PASS
WHICH SHOWS 35 KT WINDS WRAPPING INTO THE LLCC FROM THE EAST, PLACING
GOOD CONFIDENCE IN THE INITIAL INTENSITY. MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES ARE EVALUATED AT T1.5 (25 KTS, PGTW/KNES), LOWER
THAN THE CURRENT INTENSITY. OVERALL, TC 21S IS TRANSITING THROUGH A
MODERATELY FAVORABLE ENVIRONMENT WITH GOOD POLEWARD OUTFLOW, LOW TO
MODERATE (15-20 KT) VERTICAL WIND SHEAR (VWS), AND WARM (29-30
CELSIUS) SEA SURFACE TEMPERATURES (SST). TC 21S IS TRACKING ALONG THE
PERIPHERY OF A LOW- TO MID-LEVEL RIDGE SITUATED TO THE SOUTHEAST.
UNDER ITS INFLUENCE, THE SYSTEM WILL TRACK SOUTH-SOUTHWESTWARD
THROUGHOUT THE FORECAST PERIOD. BY TAU 36, THE SYSTEM WILL BE
APPROACHING THE NORTHWESTERN AUSTRALIA COAST. AT THIS POINT,
INCREASING VWS VALUES AND LAND INTERACTION WILL CAUSE THE SYSTEM TO
WEAKEN. HOWEVER, DUE TO HIGH SST PRIOR TO LANDFALL, TC 21S IS
EXPECTED TO REMAIN AS A MARGINAL SYSTEM UNTIL FULL DISSIPATION BY TAU
48, IF NOT SOONER. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT. OF
NOTE, GFS AND THE GFS ENSEMBLE MAINTAIN A MORE WESTWARD TRACK,
KEEPING THE SYSTEM OVER WATER THROUGH THE ENTIRE FORECAST. HOWEVER,
DUE TO THE GOOD AGREEMENT AMONG THE MAJORITY OF THE SOLUTIONS, THE
JTWC FORECAST TRACK IS PLACED NEAR THE MULTI-MODEL CONSENSUS WITH
GOOD CONFIDENCE. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 110600Z IS 12
FEET. NEXT WARNINGS AT 111500Z, 112100Z, 120300Z AND 120900Z.
2. THIS CANCELS AND SUPERSEDES REF A (WTXS21 PGTW 101600).//
NNNN

BoM則依然視為熱帶低壓，並不看好後續發展。

Tropical Cyclone Outlook for the Western Region
IDW10800

Tropical Cyclone Outlook for the Western Region
Issued at 2:00 pm WST on Wednesday 11 March 2020
for the period until midnight WST Saturday 14 March 2020.

Existing Cyclones in the Western Region:
##

Potential Cyclones:

A tropical low was located near 15.7S 116.8E at 11am WST Wednesday, about 560km north of Karratha and 750km north northeast of Exmouth. This system is forecast to move south southwest towards the northwest of Western Australia and lie near the far west Pilbara coast late Thursday evening or early Friday morning. This system is unlikely to develop into a tropical cyclone, however squally conditions and heavy rainfall are possible over the far western Pilbara from later on Thursday as the system moves by.

The low is expected to weaken on Friday, however moisture from the low is expected produce areas of rainfall over southwestern WA on the weekend.


Likelihood of this system being a tropical cyclone in the Western Region on:
Thursday:Low
Friday:Very Low
Saturday:Very Low

There are no other significant lows in the Western Region and none are expected to develop in the next three days.


Likelihood of another system being a tropical cyclone in the Western Region on:
Thursday:Very Low
Friday:Very Low
Saturday:Very Low

NOTES: The likelihood is an estimate of the chance of each system being a tropical cyclone in the Region for each day.
Very Low:less than 5%Low:5% to 20%
Moderate:20 to 50%High:Over 50%
The Western Region refers to the Indian Ocean between Longitudes 90-125E and south of 10S.

JTWC 09/18Z提升評級至Medium。

(1) THE AREA OF CONVECTION (INVEST 94S) PREVIOUSLY LOCATED
NEAR 11.7S 113.8E IS NOW LOCATED NEAR 11.0S 113.6E, APPROXIMATELY
647 NM NORTHWEST OF BROOME, AUSTRALIA. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY AND A 091331Z GMI 89GHZ MICROWAVE IMAGE REVEAL
ISOLATED DEEP CONVECTION WITHIN FRAGMENTED BANDING. INVEST 94S IS
CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT WITH GOOD POLEWARD
OUTFLOW, MODERATE (20 TO 25 KNOT) VERTICAL WIND SHEAR, AND WARM (29
TO 30 CELSIUS) SEA SURFACE TEMPERATURES. GLOBAL MODELS ARE IN GOOD
AGREEMENT THAT 94S WILL TURN ON A SOUTHWARD TRACK AND MAY REACH
TROPICAL STORM INTENSITY OVER THE NEXT 48 HOURS. MAXIMUM SUSTAINED
SURFACE WINDS ARE ESTIMATED AT 18 TO 23 KNOTS. MINIMUM SEA LEVEL
PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR THE
DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24
HOURS IS UPGRADED TO MEDIUM.