WPAC: CO-MAY - Post-Tropical - Discussion

[cycloneye]

Last warning from JMA.

T2508(Co-may)
Issued at 2025/07/26 00:45 UTC
Analysis at 07/26 00 UTC
Grade TD
Scale -
Intensity -
Center position N26°00′ (26.0°)
E125°00′ (125.0°)
Direction and speed of movement NNE 35 km/h (20 kt)
Central pressure 996 hPa

[Hayabusa]

JTWC thinks it's still alive and latest forecast show becoming a TS again, now that would be interesting if it becomes a TS again, would JMA reuse CO-MAY as the name or a new name?

WDPN33 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (CO-MAY)
WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
INITIAL POSITION: 26.8N 127.4E
INITIAL INTENSITY: 25 KTS
GEOGRAPHIC REFERENCE: 28 NM NORTHWEST OF KADENA AB
MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 05 KTS
SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN EXPOSED
LOW-LEVEL CIRCULATION (LLC), WITH FLARING DEEP CONVECTIVE BURSTS ALONG
THE SOUTHERN AND EASTERN PERIPHERIES. ANIMATED RADAR IMAGERY REVEALS
WEAK BANDING WRAPPING INTO AN ELONGATED LLC, WITH FRAGMENTED OUTER
BANDING. SURFACE OBSERVATIONS SUPPORT THE INITIAL POSITION WEST OF
OKINAWA, WITH MAXIMUM WINDS OF 21 KNOTS (10-MINUTE AVERAGE) REPORTED
AT KITAHARA. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON RADAR IMAGERY, EIR IMAGERY AND SURFACE OBSERVATIONS. THE
INITIAL INTENSITY OF 25 KNOTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON SURFACE OBSERVATIONS AND RECENT ASCAT DATA. ENVIRONMENTAL
CONDITIONS ARE MARGINALLY FAVORABLE, WITH MODERATE EQUATORWARD OUTFLOW
AND WEAK POLEWARD OUTFLOW, INHIBITED BY A TUTT CELL POSITIONED TO THE
NORTHWEST AND DRY AIR ENTRAINMENT OFFSET BY LOW VERTICAL WIND SHEAR
AND WARM SST VALUES.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT, WITH
SUBTROPICAL RIDGE (STR) TO THE EAST AND NORTH AND NEAR-EQUATORIAL
RIDGE (NER) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T1.5 - 25 KTS
CIMSS SATCON: 44 KTS AT 261658Z
CIMSS ADT: 32 KTS AT 261730Z
CIMSS AIDT: 35 KTS AT 261730Z
CIMSS D-MINT: 25 KTS AT 261658Z
CIMSS D-PRINT: 22 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
VWS: 10-15 KTS
SST: 28-29 CELSIUS
OUTFLOW: MODERATE EQUATORWARD
OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: MAJOR CHANGE TO THE JTWC FORECAST,
WITH SYSTEM NOW EXPECTED TO REINTENSIFY AND TRACK OVER EASTERN
CHINA.

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 11W IS FORECAST TO
TRACK SLOWLY EAST-NORTHEASTWARD THROUGH TAU 12 THEN TURN SHARPLY
NORTHWESTWARD TO WEST-NORTHWESTWARD AS THE STR TO THE NORTH BECOMES
THE DOMINANT STEERING INFLUENCE. THE SYSTEM WILL GRADUALLY INTENSIFY
TO 30 KNOTS BY TAU 24. AFTER TAU 24, TD 11W WILL ACCELERATE WEST-
NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR THROUGH
LANDFALL, WHICH WILL OCCUR SOUTH OF SHANGHAI NEAR TAU 60. TD 11W WILL
SLOWLY INTENSIFY DUE TO DRY AIR ENTRAINMENT. HOWEVER, THE SYSTEM IS
EXPECTED TO RE-MOISTEN JUST PRIOR TO LANDFALL, WITH A PEAK INTENSITY
OF 45 KNOTS NEAR TAU 60. AFTER LANDFALL, THE SYSTEM WILL RECURVE
POLEWARD OVERLAND TOWARD A BREAK IN THE STR TO THE NORTH, WITH STEADY
WEAKENING AND DISSIPATION EXPECTED.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN FAIR AGREEMENT,
WITH A 110NM CROSS-TRACK SPREAD AT TAU 48. THE DETERMINISTIC AND
ENSEMBLE MODELS DIVERGE THROUGH THE REMAINDER OF THE JTWC FORECAST,
WITH MEDIUM OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST. RELIABLE
INTENSITY GUIDANCE INDICATES A PEAK INTENSITY RANGING FROM 35 TO 45
KNOTS BETWEEN TAU 36 TO TAU 60.

FORECAST CONFIDENCE:
TRACK 0 - 72 HR: MEDIUM
TRACK 72-120 HR: MEDIUM
INTENSITY 0 - 72 HR: MEDIUM
INTENSITY 72-120 HR: MEDIUM//
NNNN

[Hayabusa]

12Z, for some reason Euro TC name tracker changed from CO-MAY to MAY

[Hayabusa]

JTWC back to TS intensity

11W CO-MAY 250727 1200 26.2N 130.4E WPAC 40 986

[Hayabusa]

JMA back to TS CO-MAY

T2508(Co-may)
Issued at 2025/07/27 13:20 UTC
Analysis at 07/27 12 UTC
Grade TS
Scale -
Intensity -
Center position N26°05′ (26.1°)
E129°35′ (129.6°)
Direction and speed of movement Almost stationary
Central pressure 992 hPa
Maximum sustained wind speed near center 18 m/s (35 kt)
Maximum wind gust speed 25 m/s (50 kt)
Radius of 30-kt wind area N500 km (270 NM)
S390 km (210 NM)
Forecast for 07/28 00 UTC
Grade TS
Intensity -
Center position of probability circle N27°25′ (27.4°)
E127°50′ (127.8°)
Direction and speed of movement NW 20 km/h (10 kt)
Central pressure 985 hPa
Maximum sustained wind speed near center 23 m/s (45 kt)
Maximum wind gust speed 35 m/s (65 kt)
Radius of probability circle 65 km (35 NM)
Forecast for 07/28 12 UTC
Grade TS
Intensity -
Center position of probability circle N27°55′ (27.9°)
E125°25′ (125.4°)
Direction and speed of movement W 20 km/h (11 kt)
Central pressure 985 hPa
Maximum sustained wind speed near center 23 m/s (45 kt)
Maximum wind gust speed 35 m/s (65 kt)
Radius of probability circle 95 km (50 NM)
Forecast for 07/29 12 UTC
Grade TS
Intensity -
Center position of probability circle N29°40′ (29.7°)
E121°55′ (121.9°)
Direction and speed of movement WNW 15 km/h (9 kt)
Central pressure 990 hPa
Maximum sustained wind speed near center 20 m/s (40 kt)
Maximum wind gust speed 30 m/s (60 kt)
Radius of probability circle 155 km (85 NM)
Forecast for 07/30 12 UTC
Grade TS
Intensity -
Center position of probability circle N31°55′ (31.9°)
E120°25′ (120.4°)
Direction and speed of movement NNW 10 km/h (6 kt)
Central pressure 990 hPa
Maximum wind speed 20 m/s (40 kt)
Maximum wind gust speed 30 m/s (60 kt)
Radius of probability circle 220 km (120 NM)
Forecast for 07/31 12 UTC
Grade TS
Intensity -
Center position of probability circle N32°40′ (32.7°)
E120°10′ (120.2°)
Direction and speed of movement Almost stationary
Central pressure 990 hPa
Maximum wind speed 20 m/s (40 kt)
Maximum wind gust speed 30 m/s (60 kt)
Radius of probability circle 280 km (150 NM)
Forecast for 08/01 12 UTC
Grade TS
Intensity -
Center position of probability circle N33°05′ (33.1°)
E120°05′ (120.1°)
Direction and speed of movement Almost stationary
Central pressure 994 hPa
Maximum wind speed 18 m/s (35 kt)
Maximum wind gust speed 25 m/s (50 kt)
Radius of probability circle 330 km (180 NM)

[cycloneye]

FORECAST DISCUSSION: TS 11W WILL REMAIN IN A COMPETING AND
CONFUSED STEERING ENVIRONMENT BETWEEN TWO RIDGES TO THE NORTH AND
SOUTH FOR THE NEXT 12 HOURS. THE TRACK WILL REMAIN WEAK AND IRREGULAR
BEFORE THE RIDGE TO THE SOUTH WEAKENS AT TAU 24, ALLOWING THE SYSTEM
TO ASSUME A WEST-NORTHWESTWARD TRACK. HOWEVER, SMALL DEVIATIONS IN
THE TRACK MOVEMENT MAY NOT BE CAPTURED WITHIN THE WARNING GRAPHIC. IF
THE RIDGE EXTENDS FARTHER SOUTH, TS 11W MAY TRACK CLOSER TO
OKINAWA OR SOUTH OF THE ISLAND. THE SYSTEM WILL CONTINUE TO ROUND THE
SOUTHWESTERN QUADRANT OF THE SUBTROPICAL RIDGE CURVING TO THE
NORTHWEST. LANDFALL WILL OCCUR IMMEDIATELY FOLLOWING TAU 72,
LEADING TO DISSIPATION BY TAU 120. RAPID INTENSIFICATION IS
POSSIBLE DURING THE NEXT 24 HOURS AS THE UPPER-LEVEL CYCLONE TO
THE NORTHWEST FILLS. THE UPPER-LEVEL ENVIRONMENT WILL BECOME HIGHLY
FAVORABLE WITH DUAL-CHANNEL OUTFLOW. THE VERTICAL WIND SHEAR WILL
REMAIN FAVORABLE AND SEA SURFACE TEMPERATURES WILL CONTINUE TO BE
WARM THROUGH TAU 48. AFTER TAU 48, VERTICAL WIND SHEAR WILL
INCREASE UNFAVORABLY TO 15-20 KTS, AND INITIATE A WEAKENING PHASE.
THE SYSTEM WILL WEAKEN GRADUALLY PRIOR TO LANDFALL BEFORE TAU 72.
AFTER TAU 72, TOPOGRAPHIC INTERACTION WILL WEAKEN THE SYSTEM TO
DISSIPATION BY TAU 120.

[cycloneye]

FORECAST DISCUSSION: TS 11W APPEARS TO BE TRACKING WESTWARD AS OF
271930Z AS ANTICIPATED AND IS FORECAST TO CONTINUE TRACKING WESTWARD
TO WEST-NORTHWESTWARD THROUGH TAU 48 ALONG THE SOUTHERN PERIPHERY OF
THE DOMINANT STEERING INFLUENCE TO THE NORTH. GRADUAL INTENSIFICATION
IS EXPECTED AS THE SYSTEM MOISTENS AND DRY AIR ENTRAINMENT DECREASES.
ADDITIONALLY, THE UPPER LOW TO THE WEST IS EXPECTED TO WEAKEN AND
SHIFT SOUTHWESTWARD OVER TAIWAN, WHICH WILL ENHANCE POLEWARD OUTFLOW.
AS THE SYSTEM TRACKS WESTWARD OVER THE NEXT 12 TO 24 HOURS, THE GALE
FORCE WINDS ALONG THE EASTERN FLANK MAY SHIFT WESTWARD AND IMPACT
OKINAWA. AFTER TAU 48, THE SYSTEM WILL RECURVE POLEWARD OVERLAND, WITH
STEADY WEAKENING AND DISSIPATION BY TAU 120.

[cycloneye]

INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 11W IS EMBEDDED WITHIN A VERY LARGE AREA OF LOW
PRESSURE (MONSOON DEPRESSION CHARACTERISTICS), WITH PERIPHERAL WINDS
OF 35-40 KNOTS WITHIN THE TIGHT GRADIENT ON THE EASTERN PERIPHERY OF
THE SYSTEM. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
AN ELONGATED, PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH CONVECTIVE BANDING DISPLACED OVER THE EASTERN SEMICIRCLE.
HOWEVER, EIR IMAGERY FROM 271800-1930Z SHOWS AN EXPOSED, DEFINED LLCC
TRACKING TOWARD THE NORTHERN TIP OF OKINAWA. THIS UPDATED CENTER AT
271930Z IS LOCATED ABOUT 26.81N 128.44E. THIS 271930Z POSITION IS
SUPPORTED BY MULTIPLE SURFACE OBSERVATIONS FROM THE JMA WEBSITE, WHICH
SHOW NORTHERLY TO NORTHWESTERLY WINDS OVER OKINAWA. MAXIMUM WINDS
REPORTED ARE FROM BOTH OKINOERABU AND ISEN (ISLANDS NORTH-NORTHEAST OF
OKINAWA), WITH 26-27 KNOT EASTERLY WINDS (10-MINUTE AVERAGE). SURFACE
WINDS ACROSS OKINAWA ARE LESS THAN 20 KNOTS. AS INDICATED IN ANIMATED
RADAR IMAGERY, TS 11W HAS BECOME BETTER ORGANIZED, WITH CONVECTIVE
BANDING OVER THE SOUTHERN AND EASTERN QUADRANTS AND AN ILL-DEFINED
LLCC AT 271800Z. ANIMATED WATER VAPOR IMAGERY REVEALS AN UPPER LOW
POSITIONED TO THE WEST, WHICH IS HINDERING CONVECTIVE DEVELOPMENT
OVER THE WESTERN SEMICIRCLE, WITH ROBUST EASTWARD AND EQUATORWARD
OUTFLOW FUELING THE PERSISTENT DEEP CONVECTION OVER THE EASTERN
SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE ANIMATED EIR IMAGERY, SURFACE OBSERVATIONS AND RADAR
IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK ESTIMATES AS WELL AS THE
CIMSS ADT AND AIDT OBJECTIVE ESTIMATES. AS MENTIONED EARLIER, THERE
ARE STRONG GALE FORCE WINDS DISPLACED ABOUT 100 NM EAST OF THE
CENTER. THESE PERIPHERAL WINDS WERE REFLECTED IN THE MINAMIDAITO-JIMA
OBSERVATIONS BUT HAVE SINCE DECREASED TO ABOUT 20 KNOTS.

[Hayabusa]

Both systems are struggling after the burst of deep convection last night

[cycloneye]

FORECAST DISCUSSION: TD 11W WILL CONTINUE TO BE DRIVEN
NORTHWESTWARD UNDER THE WEAK STEERING INFLUENCE OF THE SUBTROPICAL
RIDGE TO THE NORTH FOR THE NEXT 24 HOURS. AFTER TAU 24, THE SYSTEM
WILL CURVE NORTHWARD WHILE ROUNDING THE SOUTHWESTERN QUADRANT OF
THE RIDGE. AFTER TAU 96, THE SYSTEM WILL CURVE NORTHEASTWARD ON THE
LOW-LEVEL FLOW AS A DISSIPATED SYSTEM. TD 11W WILL REMAIN IN A
MARGINAL ENVIRONMENT FOR DEVELOPMENT FOR THE FIRST 12 HOURS OF THE
FORECAST PERIOD DUE TO MODERATE VERTICAL WIND SHEAR AND DRY AIR
ENTRAINMENT FROM THE UPPER-LEVEL CYCLONE TO THE NORTHWEST. VERTICAL
WIND SHEAR WILL DECREASE FAVORABLY AFTER TAU 24, ALLOWING FOR
GRADUAL REINTENSIFICATION AS THE CYCLONE DRIFTS WESTWARD AND
BECOMES WEAK. THE SYSTEM WILL CONTINUE TO INTENSIFY UNDER A
MARGINALLY FAVORABLE ENVIRONMENT TO A PEAK OF 40KTS BY TAU 48. THE
SYSTEM WILL MAKE LANDFALL BETWEEN TAU 48-72, INITIATING A
DISSIPATION DUE TO TOPOGRAPHIC INTERACTION. AFTER TAU 96, THE
SYSTEM WILL PASS INTO THE YELLOW SEA, BUT STRONG VERTICAL WIND
SHEAR AND AN UPPER-LEVEL TROUGH ALOFT WILL INHIBIT REDEVELOPMENT.

[cycloneye]

Wow, it has been a long journey with back and forths while is has been looping around, but the dead end will come shortly.

[StormWeather]

Wow, it has been a long journey with back and forths while is has been looping around, but the dead end will come shortly.

https://i.imgur.com/ntFnamJ.gif

How is this thing still going??!

[cycloneye]

Finnally is over for this system.

REMARKS:
301500Z POSITION NEAR 31.4N 121.1E.
30JUL25. TROPICAL STORM 11W (CO-MAY), LOCATED APPROXIMATELY 5 NM
WEST OF SHANGHAI, CHINA, HAS TRACKED NORTHWESTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS.3 ANIMATED ENHANCED INFRARED IMAGERY
(EIR) REVEALS THE BROAD AND RAGGED CIRCULATION OF TROPICAL STORM
(TS) 11W DEGRADING OVER THE COAST. A DEEP-LAYER TROUGH TO THE
NORTH STRONGLY ENHANCES POLEWARD OUTFLOW, BUT ALSO INTRODUCES
UNFAVORABLE HIGH VERTICAL WIND SHEAR. TS 11W WILL CONTINUE TO
DISSIPATE FOR THE NEXT 36 HOURS DUE TO TOPOGRAPHIC INTERACTION.
IT IS POSSIBLE THAT THE REMNANTS OF TS 11W WILL TRACK INTO THE
YELLOW SEA, BUT THERE IS LOW LIKELIHOOD OF REDEVELOPMENT DUE TO
UNFAVORABLE DRY AIR, HIGH VERTICAL WIND SHEAR, AND UPPER-LEVEL
TROUGHING. THIS IS THE FINAL WARNING ON THIS SYSTEM BY THE JOINT
TYPHOON WRNCEN PEARL HARBOR HI.