SPAC: 01F - Post-Tropical

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Nancy Smar
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SPAC: 01F - Post-Tropical

#1 Postby Nancy Smar » Mon Dec 07, 2020 6:36 pm

90P INVEST 201207 1800 13.0S 170.0W SHEM 15 0
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Re: SPAC: 01F - Tropical Depression (04P)

#2 Postby doomhaMwx » Fri Dec 11, 2020 5:20 am

For the record, this has been upgraded to TS 04P by JTWC (Tropical Depression 01F by FMS). As JTWC mentions, 04P is expected to interact with nearby developing Invest 91P, making the forecast highly-uncertain. 91P might actually turn out to be the dominant system though. Models show the merged system becoming a significant cyclone between Fiji and Vanuatu in the coming days.

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REMARKS:
110900Z POSITION NEAR 13.1S 178.5E.
11DEC20. TROPICAL CYCLONE (TC) 04P (FOUR), LOCATED APPROXIMATELY 313NM NORTH OF SUVA, FIJI, HAS TRACKED SOUTHWESTWARD AT 08 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH PERSISTENT DEEP CONVECTION SHEARED TO THE NORTHEAST. AN 110617Z MHS 89GHZ COMPOSITE MICROWAVE IMAGE INDICATES SHALLOW BANDING WRAPPING INTO THE LLCC, SUPPORTING THE INITIAL POSITION WITH GOOD CONFIDENCE. THE INITIAL INTENSITY REMAINS ASSESSED AT 35 KNOTS BASED ON A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF 2.5 (35 KNOTS) AND AN 110630Z ADT ESTIMATE OF 2.5. UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT WITH STRONG (25-30 KNOTS) VERTICAL WIND SHEAR OFFSET BY DIFFLUENT FLOW ALOFT AND WARM SST VALUES (29-30C). TC 04P IS EXPECTED TO TRACK GENERALLY WESTWARD THROUGH TAU 48 ALONG THE NORTHERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE SOUTH. THE SYSTEM IS ALSO TRACKING ALONG THE SOUTHERN PERIPHERY OF A LARGE MONSOON DEPRESSION (INVEST 91P), WHICH IS FORECAST TO GRADUALLY INTENSIFY OVER THE NEXT 1-2 DAYS INTO A CONSOLIDATED TROPICAL CYCLONE. DUE TO THE PROXIMITY OF INVEST 91P TO TC 04P, THERE WILL BE A LIKELY PHASE OF DIRECT CYCLONE INTERACTION (DCI) AND POSSIBLE FUJIWHARA/MERGER NEAR TAU 72. THIS COMPLEX SCENARIO INVOLVES A LARGE DEGREE OF UNCERTAINTY IN THE TRACK FORECAST AND INTENSITY FORECAST. GFS AGGRESSIVELY DEVELOPS INVEST 91P AND WEAKENS TC 04P LEADING TO 04P'S ABSORPTION WHILE NAVGEM/ECMWF INDICATE GRADUAL DEVELOPMENT OF INVEST 91P AND ABSORPTION OF TC 04P. DUE TO THE DCI/FUJIWHARA SCENARIO, THE JTWC FORECAST TRACK REFLECTS A SLOW/QUASI-STATIONARY MOTION FROM TAU 48 TO TAU 96. BY TAU 96, THE STR IS FORECAST TO BUILD TO THE EAST AND NORTHEAST AS A DEEP SHORTWAVE TROUGH APPROACHES. THUS, TC 04P WILL BEGIN TO TRACK POLEWARD BY TAU 120. TC 04P IS FORECAST TO STRUGGLE THROUGH TAU 48 WITH A SLIGHT INTENSIFICATION. AFTER TAU 48, THE MERGED SYSTEM SHOULD GRADUALLY INTENSIFY AS THE ENVIRONMENT IMPROVES WITH STEADY INTENSIFICATION TO A PEAK OF 80 KNOTS BY TAU 120. DUE TO THE UNUSUAL COMPLEXITY OF THIS FORECAST SCENARIO, THERE IS AN ALTERNATE SCENARIO WHERE INVEST 91P BECOMES THE DOMINANT SYSTEM AND TC 04P DISSIPATES. NUMERICAL MODEL GUIDANCE REMAINS IN POOR AGREEMENT LENDING LOW CONFIDENCE TO THE JTWC FORECAST TRACK. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 110600Z IS 12 FEET. NEXT WARNINGS AT 111500Z, 112100Z, 120300Z AND 120900Z.//
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Re: SPAC: 01F - Tropical Depression (04P)

#3 Postby doomhaMwx » Fri Dec 11, 2020 5:32 am

TROPICAL DEPRESSION TD01F [1000HPA] WAS ANALYSED NEAR 13.0S 179.0E
AT 110600UTC. TD01F MOVING WEST-SOUTHWEST AT ABOUT 08 KNOTS. POSITION
POOR.
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Re: SPAC: 01F - Tropical Depression (04P)

#4 Postby aspen » Fri Dec 11, 2020 6:22 pm

The LLC is racing ahead of the extremely sheared convection. Looks like it’s in the process of being destroyed and absorbed by 91P.
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Re: SPAC: 01F - Tropical Depression (04P)

#5 Postby doomhaMwx » Sat Dec 12, 2020 1:07 am

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TROPICAL DISTURBANCE ADVISORY NUMBER A4 ISSUED FROM RSMC NADI
Dec 120152 UTC.

TROPICAL DEPRESSION TD01F CENTRE [1000HPA] WAS LOCATED NEAR 14.8S
176.2E AT 120000 UTC. POSITION GOOD BASED ON HIMAWARI-8 VIS/IR
IMAGERY AND PERIPHERY SURFACE REPORTS. TD01F MOVING SOUTHWEST AT
ABOUT 15 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE
ESTIMATED AT ABOUT 30 KNOTS.

CONVECTION SHEARED TO THE NORTHEAST OF FULLY EXPOSED LLCC.
ORGANISATION REMAINS POOR. SYSTEM LIES TO THE SOUTH FO AN UPPER RIDGE
IN A HIGH SHEARED ENVIRONMENT. SST IS AROUND 29 DEGREES CELSIUS.
TD01F IS BEING STEERED TO THE SOUTHWEST BY THE NORTHERN PERIPHERY OF
THE SUBTROPICAL RIDGE LOCATED TO THE SOUTHEAST OF THE SYSTEM.
DVORAK ANALYSIS BASED ON SHEARED PATTERN, WITH CENTRE SHEARED TO
ABOUT 90NM, YIELDING DT=2.0. MET AND PAT AGREE. FT BASED ON DT THUS,
YIELDING T2.0/2.5/W0.5/24HRS

FORECASTS :
AT 12 HRS VALID AT 121200 UTC 15.5S 174.5E MOV WSW AT 09 KT WITH 30
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 130000 UTC 15.8S 173.3E MOV WSW AT 07 KT WITH 30
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 131200 UTC 16.1S 172.9E MOV WSW AT 06 KT WITH 30
KT CLOSE TO CENTRE
AT 48 HRS VALID AT 140000 UTC 16.4S 172.9E MOV WSW AT 05 KT WITH 30
KT CLOSE TO CENTRE

THE WILL BE THE LAST TROPICAL DISTURBANCE ADVISORY ON TD01F UNLESS IT
RE-INTENSIFIES.


Final warning from JTWC as well.
REMARKS:
121500Z POSITION NEAR 15.7S 172.9E.
12DEC20. TROPICAL CYCLONE 04P (FOUR), LOCATED APPROXIMATELY
337 NM WEST-NORTHWEST OF SUVA, FIJI, HAS TRACKED WESTWARD AT
14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS DISORGANIZED, FLARING
CONVECTION OBSCURING A LOW LEVEL CIRCULATION CENTER (LLCC).
THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON
THE POSITION OF THE LLCC IN THE EIR LOOP AS WELL AS VIA
EXTRAPOLATION THROUGH CONVECTIVE BANDING FEATURES PRESENT IN
A 120957Z AMSU COLOR COMPOSITE IMAGE. THE INITIAL INTENSITY
IS ASSESSED AT 35 KTS BASED ON A CIMSS ADVANCED DVORAK
TECHNIQUE CURRENT INTENSITY ESTIMATE OF T2.5 (35 KTS) AND THE
PRESENCE OF 35 KTS WINDS ALONG THE SOUTHEASTERN PERIPHERY OF
THE SYSTEM IN DATA FROM A 120844Z ASCAT-A PASS. THE SYSTEM IS
TRACKING ALONG THE NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE
POSITIONED TO THE SOUTH AND THROUGH A FAVORABLE ENVIRONMENT
WITH LOW (10-15 KTS) VERTICAL WIND SHEAR, WARM (28-29 CELSIUS)
SEA SURFACE TEMPERATURES (SST) AND DIVERGENT OUTFLOW ALOFT.
DESPITE THESE FAVORABLE CONDITIONS, THE SYSTEM HAS WEAKENED
SIGNIFICANTLY OVER THE PAST 12 HOURS AS IT ENTERED THE CAPTURE
PHASE OF A DIRECT CYCLONE INTERACTION (DCI) WITH TC 05P WHICH
IS LOCATED 115 NM NORTH OF THE SYSTEM CENTER. OVER THE NEXT 12
HOURS TC 04P WILL CONTINUE TO WEAKEN AND DISSIPATE OVER WATER
AS IT ENTERS AND COMPLETES THE MERGER PHASE OF THIS DCI AND
BECOMES INCORPORATED INTO TC 05P. NUMERICAL MODELS ARE IN FAIR
AGREEMENT DURING THIS 12 HOUR FORECAST AND THUS LEND FAIR
CONFIDENCE IN THE JTWC FORECAST TRACK WHICH IS PLACED SLIGHTLY
EQUATORWARD OF THE JTWC MULTI-MODEL CONSENSUS. THIS IS THE
FINAL WARNING ON THIS SYSTEM BY THE JOINT TYPHOON WRNCEN PEARL
HARBOR HI. THE SYSTEM WILL BE CLOSELY MONITORED FOR SIGNS OF
REGENERATION. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 121200Z IS 14
FEET. REFER TO TROPICAL CYCLONE 05P (FIVE) WARNINGS (WTPS31
PGTW) FOR SIX-HOURLY UPDATES.
//
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Re: SPAC: 01F - Tropical Depression (04P)

#6 Postby aspen » Sat Dec 12, 2020 9:12 pm

This has been fully consumed by 05P.
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