SPAC: YASA - Post Tropical

[doomhaMwx]

91P INVEST 201211 0600 11.0S 170.5E SHEM 25 1001
91P INVEST 201211 0000 10.9S 170.4E SHEM 25 1001
91P INVEST 201210 1800 10.9S 170.2E SHEM 25 1002
91P INVEST 201210 1200 10.8S 170.0E SHEM 25 1004

TROPICAL DISTURBANCE TD02F CENTRE [1004HPA] WAS LOCATED NEAR 12.8S
169.4E AT 110600 UTC. TD02F MOVING SOUTH-SOUTHWEST AT ABOUT 23 KNOTS.
POSITION POOR.

[doomhaMwx]

Quoting from the TD 01F (TS 04P) thread.

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.

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.//
NNNN

[doomhaMwx]

ABPW10 PGTW 110600

THE AREA OF CONVECTION (INVEST 91P) PREVIOUSLY LOCATED
NEAR 10.9S 170.4E IS NOW LOCATED NEAR 10.9S 170.4E, APPROXIMATELY
423 NM NORTH-NORTHEAST OF PORT VILA, VANUATU. ANIMATED ENHANCED
INFRARED SATELLITE IMAGERY AND AN 110151Z AMSR2 89GHZ MICROWAVE
IMAGE DEPICT A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER WITH
SOME FLARING CONVECTION IN THE NORTHEASTERN SEMICIRCLE. A 102032Z
ASCAT-A PASS REVEALS AN ASYMMETRIC LLCC WITH 30 TO 35 KNOT WINDS TO
THE EAST AND WEAKER (5-10KT) WINDS TO THE SOUTHWEST. INVEST 91P IS
CURRENTLY IN A FAVORABLE ENVIRONMENT WITH STRONG OUTFLOW ALOFT, LOW
TO MODERATE (10-20KTS) VERTICAL WIND SHEAR, AND WARM (29-30C) SEA
SURFACE TEMPERATURES. GLOBAL MODELS ARE SOMEWHAT SPLIT WITH ECMWF
AND UKMET SHOWING THAT INVEST 91P WILL TRACK SOUTHEASTWARD, BECOMING
ABSORBED INTO TROPICAL CYCLONE 04P. GFS AND NAVGEM ARE SHOWING THAT
INVEST 91P WILL BECOME THE DOMINANT CIRCULATION, INTENSIFYING AND
EVENTUALLY ABSORBING TC 04P. MAXIMUM SUSTAINED SURFACE WINDS ARE
ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED
TO BE NEAR 1001 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.

[mrbagyo]

91P INVEST 201211 1200 12.6S 169.5E SHEM 25 1002

[aspen]

With solid banding and a CDO that has persisted for a good portion of the day, 91P is looking like a much better TC than 04P. It’ll likely be the dominant system that bombs out into the C2+ system forecast by much of the models.

[aspen]

This is what is called a "bruh moment".

[ElectricStorm]

This is what is called a "bruh moment".
https://i.imgur.com/PgYA3SZ.png

I smell a forecast change coming...

[doomhaMwx]

This is what is called a "bruh moment".
https://i.imgur.com/PgYA3SZ.png

That looks right, actually. Latest ASCAT didn't find a closed circulation yet in 91P but one is probably consolidating underneath the western part of that very deep convection (~170E). 04P is indeed still holding on to TS intensity.

[aspen]

This is what is called a "bruh moment".
https://i.imgur.com/PgYA3SZ.png

That looks right, actually. Latest ASCAT didn't find a closed circulation yet in 91P but one is probably consolidating underneath the western part of that very deep convection (~170E). 04P is indeed still holding on to TS intensity.

https://i.imgur.com/yZoaGC3.png
https://i.imgur.com/1iKoX2e.png

I’m not denying that 04P is a TS; its LLC is clearly visible. However, it’s quickly outrunning sheared convection that is melding into 91P’s expansive outflow. It should be long before 91P develops its own defined LLC and swallows up whatever is left of 04P.

[doomhaMwx]

TROPICAL DISTURBANCE ADVISORY NUMBER B1 ISSUED FROM RSMC NADI
Dec 120214 UTC.

TROPICAL DEPRESSION TD02F CENTRE [1000HPA] WAS LOCATED NEAR 12.7S
170.7E AT 120000 UTC. POSITION POOR BASED ON HIMAWARI-8 VIS IMAGERY
AND PERIPHERY SURFACE REPORTS.
TD02F MOVING SOUTH-SOUTHEAST AT ABOUT 05 KNOTS. MAXIMUM 10-MINUTE
AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 30 KNOTS.

CONVECTION REMAINED PERSISTANT OVER LLCC. ORGANISATION REMAINS POOR.
SYSTEM LIES UNDER AN UPPER RIDGE IN A LOW SHEARED ENVIRONMENT. SST IS
AROUND 30 DEGREES CELSIUS. TD02F IS SLOW MOVING. DVORAK ANALYSIS
BASED ON CURVED PATTERN, WITH 0.25 WRAP ON LOG 10 SPIRAL, YIELDING
DT=2.5. MET AND PAT AGREE. FT BASED ON DT THUS, YIELDING
T2.5/2.5/D0.5/24HRS.

FORECASTS :

AT 12 HRS VALID AT 121200 UTC 13.4S 171.9E MOV ESE AT 07 KT WITH 30
KT CLOSE TO CENTRE
AT 24 HRS VALID AT 130000 UTC 14.3S 172.6E MOV SE AT 06 KT WITH 35 KT
CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 131200 UTC 15.0S 172.6E MOV SE AT 05 KT WITH 45 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 140000 UTC 15.4S 172.4E MOV SSE AT 04 KT WITH 50
KT CLOSE TO CENTRE

WTPS21 PGTW 120330

REMARKS: THE AREA OF CONVECTION (INVEST 91P) PREVIOUSLY LOCATED
NEAR 10.9S 170.4E IS NOW LOCATED NEAR 12.6S 170.1E, APPROXIMATELY
321 NM NORTH-NORTHEAST OF PORT VILA, VANUATU. ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) DEPICTS CONVECTIVE BANDS SPIRALING INTO A
LOW LEVEL CIRCULATION CENTER (LLCC). A PARTIAL 112125Z METOP-B 89GHZ
SATELLITE IMAGE REVEALS A POCKET OF DEEP CONVECTION TO THE
SOUTHEASTERN PERIPHERY. INVEST 91P IS IN A FAVORABLE ENVIRONMENT FOR
DEVELOPMENT WITH RADIAL OUTFLOW, LOW (0-15 KT) VERTICAL WIND SHEAR
(VWS), AND WARM (29-30C) SEA SURFACE TEMPERATURES (SST). GLOBAL
MODELS GENERALLY AGREE THAT INVEST 91P WILL REMAIN QUASI-STATIONARY
OVER THE NEXT 24 HOURS WHILE CONSOLIDATING BEFORE TURNING TO A
SOUTHEASTERLY TRACK. DURING THIS TRACK, THE SYSTEM WILL LIKELY BEGIN
DIRECT CYCLONE INTERACTION WITH TROPICAL CYCLONE 04P, POSITIONED TO
THE SOUTHEAST, AND MAY RESULT IN A FUJIWHARA EFFECTS THEREAFTER.
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 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 HIGH.

[doomhaMwx]

05P FIVE 201212 1200 13.7S 172.9E SHEM 35 1000

Srfc circulation has definitely become much more improved/defined on the most recent ASCAT pass. This pass also clearly shows 04P just ~260km from 05P as the two undergoes Fujiwhara interaction.

[aspen]

The models are getting slightly more aggressive with this system. The most recent HWRF run shows a 125 kt/927 mbar Category 4, but based on its predicted IR satellite presentation, it could be stronger. 04P is likely to stall somewhere between Vanuatu and Fiji, so upwelling will become a significant issue eventually.

[doomhaMwx]

JTWC first warning has 110kts peak. Next name to be used in the SPac is "Yasa".

REMARKS:
121500Z POSITION NEAR 14.0S 172.9E.
12DEC20. TROPICAL CYCLONE (TC) 05P (FIVE), LOCATED APPROXIMATELY
413 NM NORTHWEST OF SUVA, FIJI, HAS TRACKED SOUTH-SOUTHEASTWARD
AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
(EIR) SATELLITE IMAGERY DEPICTS SPIRAL CONVECTIVE BANDS WRAPPING
INTO A LOW LEVEL CIRCULATION CENTER (LLCC) THAT IS PARTIALLY
OBSCURED BY DEEP CONVECTION. THE INITIAL POSITION IS PLACED WITH
FAIR CONFIDENCE BASED ON THE POSITION OF THE LLCC IN THE EIR
LOOP AS WELL AS THROUGH THE LOW LEVEL BANDING FEATURES PRESENT IN
A 120958Z AMSU COLOR COMPOSITE IMAGE. THE INITIAL INTENSITY IS
HEDGED SLIGHTLY HIGHER THAN A KNES DVORAK CURRENT INTENSITY
ESTIMATE OF T2.0 (30 KTS) BASED ON THE 35 KTS WINDS PRESENT IN
DATA FROM A 120844Z ASCAT-A PASS. THE WIND FIELD PRESENT IN THE
ASCAT-A PASS REVEALS THAT THE LOW LEVEL STRUCTURE REMAINS BROAD
AND ALSO CONSTRAINS THE INITIAL POSITION. TC 05P IS TRACKING
ALONG THE NORTHERN PERIPHERY OF A DEEP LAYER SUBTROPICAL RIDGE
(STR) POSITIONED TO THE SOUTH AND THROUGH A MARGINALLY FAVORABLE
ENVIRONMENT WITH WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES
(SST) AND MODERATE POLEWARD AND ROBUST EQUATORWARD OUTFLOW ALOFT
OFFSET SLIGHTLY BY MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS).
THE SYSTEM IS CURRENTLY UNDERGOING DIRECT CYCLONE INTERACTION
(DCI) WITH TC 04P WHICH LIES 115 NM TO THE SOUTH OF THE SYSTEM
CENTER. THE COMPLEX INTERACTION BETWEEN THESE TWO SYSTEMS RESULTS
IN A HIGH DEGREE OF UNCERTAINTY IN THE TRACK AND INTENSITY FORECAST
AS NUMERICAL MODELS STRUGGLE TO CONVERGE ON A COHERENT SOLUTION.
THE MAJORITY OF MODEL TRACK GUIDANCE SUGGESTS THAT TC 05P WILL
TRACK GENERALLY SOUTHWESTWARD AND GRADUALLY INTENSIFY DURING THE
CURRENT CAPTURE AND SUBSEQUENT MERGER PHASE OF DCI THROUGH TAU 72.
DURING THIS TIME, A REPOSITIONING OF THE STEERING STR WILL TAKE
PLACE DUE TO AN INCOMING MIDLATITUDE TROUGH WHICH PROPAGATES FROM
THE WEST. AS THE STR WEAKENS AND RETREATS TO THE EAST, IT WILL
BEGIN TO STEER THE SYSTEM GENERALLY SOUTHEASTWARD. THE MAJORITY OF
MODELS TRACK GUIDANCE AGREES THAT THIS CHANGE IN STORM MOTION WILL
OCCUR AT TAU 72, HOWEVER THE GALWEM MODEL PROVIDES A NORTHEASTWARD
MOTION FROM TAU 72 TO TAU 96 WITH A SOUTHEASTWARD TRACK MOTION
THEREAFTER. ULTIMATELY, TC 05P IS FORECAST TO TRACK SOUTHEASTWARD
THROUGH TAU 48, WHEREUPON IT WILL BECOME QUASI-STATIONARY THROUGH
TAU 72 DUE TO THE WEAKENING AND REPOSITIONING OF THE STR.
THEREAFTER TC 05P WILL TRACK GENERALLY SOUTHEASTWARD DURING THE
FINAL PORTION OF THE JTWC FORECAST THROUGH TAU 120. THE DYNAMIC
NATURE OF THE BINARY INTERACTION, COUPLED WITH THE REPOSITIONING OF
THE STEERING RIDGE, RESULTS IN A LARGE SPREAD IN MODEL TRACK
SOLUTIONS WITH A MAXIMUM ACROSS TRACK SPREAD OF 280 NM BY TAU 120.
THIS HIGH SPREAD IN MODEL SOLUTIONS LENDS OVERALL LOW CONFIDENCE IN
THE JTWC FORECAST TRACK WHICH IS PLACED EAST OF THE JTWC MULTI-MODEL
CONSENSUS TO OFFSET THE AFUM TRACK WHICH BRINGS THE VORTEX FARTHER
WEST. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 121200Z IS 16 FEET. NEXT
WARNINGS AT 122100Z, 130300Z, 130900Z AND 131500Z. REFER TO TROPICAL
CYCLONE 04P (FOUR) WARNINGS (WTPS33 PGTW) FOR THE FINAL WARNING ON
THIS SYSTEM.//
NNNN

[aspen]

12z HWRF is a little weaker, but it's been consistent with structure and a RI phase starting on Monday and peaking on Tuesday. This could be a very close call for the islands of Vanuatu.

[doomhaMwx]

05P FIVE 201213 1200 15.5S 172.6E SHEM 45 995

TROPICAL DISTURBANCE ADVISORY NUMBER B5 ISSUED FROM RSMC NADI
Dec 131403 UTC.

TROPICAL CYCLONE YASA CENTRE 995HPA WAS LOCATED NEAR 15.7S 172.3E AT
131200 UTC. POSITION GOOD POOR BASED ON HIMAWARI-8 IR IMAGERY AND
PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTH SOUTHWEST AT ABOUT
5 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED
AT ABOUT 35 KNOTS.

EXPECT WINDS ABOVE 33 KNOTS WITHIN 180 NAUTICAL MILES IN NE QUADRANT
AND WITHIN 180 NAUTICAL MILES IN SE QUADRANT
AND WITHIN 120 NAUTICAL MILES IN SW QUADRANT
AND WITHIN 120 NAUTICAL MILES IN NW QUADRANT.

DEEP CONVECTION WRAPPING ONTO SUPPOSED LLCC WITH OVERALL ORGANISATION
IMPROVING. SYSTEM LIES UNDER AN UPPER RIDGE IN A LOW SHEARED
ENVIRONMENT WITH GOOD OUTFLOW TO THE SOUTH AND NORTH. CYCLONIC
CIRCULATION EXTENDS UPTO 500HPA. SST IS AROUND 30 DEGREES CELSIUS.
DVORAK ANALYSIS BASED ON CURVED PATTERN, WITH 0.60 WRAP ON LOG 10
SPIRAL, YIELDING DT=3.0. MET AND PT AGREE. FT BASED ON DT THUS,
YIELDING T3.0/3.0/D0.5/24HRS.

GLOBAL MODELS MOVE THE SYSTEM IN NORTHWARD TRACK AND THEN
SOUTHEASTWARDS WITH FURTHER INTENSIFICATION.

FORECASTS :
AT 12 HRS VALID AT 140000 UTC 16.3S 171.7E MOV SW AT 04 KT WITH 45 KT
CLOSE TO CENTRE
AT 24 HRS VALID AT 141200 UTC 16.2S 171.2E MOV WSW AT 03 KT WITH 50
KT CLOSE TO CENTRE

OUTLOOK :
AT 36 HRS VALID AT 150000 UTC 15.7S 170.8E MOV W AT 02 KT WITH 60 KT
CLOSE TO CENTRE
AT 48 HRS VALID AT 151200 UTC 15.2S 170.8E MOV WNW 02 KT WITH 65 KT
CLOSE TO CENTRE.

[doomhaMwx]

TROPICAL DISTURBANCE ADVISORY NUMBER B5 ISSUED FROM RSMC NADI
Dec 131403 UTC.

TROPICAL CYCLONE YASA CENTRE 995HPA WAS LOCATED NEAR 15.7S 172.3E AT 131200 UTC. POSITION GOOD POOR BASED ON HIMAWARI-8 IR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTH SOUTHWEST AT ABOUT 5 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 35 KNOTS.

...

Don't know if it's "good" or "poor", but don't they ever look at scatterometer data?

[aspen]

TROPICAL DISTURBANCE ADVISORY NUMBER B5 ISSUED FROM RSMC NADI
Dec 131403 UTC.

TROPICAL CYCLONE YASA CENTRE 995HPA WAS LOCATED NEAR 15.7S 172.3E AT 131200 UTC. POSITION GOOD POOR BASED ON HIMAWARI-8 IR IMAGERY AND PERIPHERAL SURFACE REPORTS. CYCLONE MOVING SOUTH SOUTHWEST AT ABOUT 5 KNOTS. MAXIMUM 10-MINUTE AVERAGE WINDS NEAR THE CENTRE ESTIMATED AT ABOUT 35 KNOTS.

...

Don't know if it's "good" or "poor", but don't they ever look at scatterometer data?

https://i.imgur.com/pLcEFpb.jpg

Considering how many tropical storms are not classified in the eastern hemisphere despite ASCAT data, I’m assuming the answer is no.

[aspen]

An eyewall is almost fully formed as of 15-16z.

[ElectricStorm]

Starting to get pretty concerned for Fiji on this one. Each JTWC forecast shifts it a little closer. And it could be a Cat 3/4 by the time it gets there

[doomhaMwx]

05P YASA 201214 0600 15.8S 171.7E SHEM 65 981