WPAC: KROSA - Post-Tropical - Discussion

[Hurricane2022]

Good job, JMA!

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

[StormWeather]

Good job, JMA!
https://i.imgur.com/KQyIiJ7.jpeg https://i.imgur.com/2fqwGZt.jpeg

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

I’m might be missing the obvious, but what is this about?

[Hurricane2022]

Good job, JMA!
https://i.imgur.com/KQyIiJ7.jpeg https://i.imgur.com/2fqwGZt.jpeg

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

I’m might be missing the obvious, but what is this about?

JMA thinks that the weak Typhoon Krosa is stronger than the C3 Typhoon Danas.

[StormWeather]

Good job, JMA!
https://i.imgur.com/KQyIiJ7.jpeg https://i.imgur.com/2fqwGZt.jpeg

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

I’m might be missing the obvious, but what is this about?

JMA thinks that the weak Typhoon Krosa is stronger than the C3 Typhoon Danas.

[cycloneye]

JTWC up to 60kt.

12W KROSA 250727 0000 20.1N 144.9E WPAC 60 983

[Hurricane2022]

Now up to 75 kt per JMA

Scale Large

Intensity/Category Typhoon

Center Position 20.4N 145.4E

Direction and speed of movement N 20km/h (10kt)

Central pressure 965hPa

Maximum wind speed near center 40m/s (75kt)

Maximum wind gust speed 55m/s (105kt)

≥ 50-kt wind area ALL 130km (70NM)

≥ 30-kt wind area SE 650km (350NM) NW 440km (240NM)

[sasha_B]

Good job, JMA!
https://i.imgur.com/KQyIiJ7.jpeg https://i.imgur.com/2fqwGZt.jpeg

The posts in this forum are NOT official forecasts and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or STORM2K. For official information, please refer to products from the NHC and NWS.

I’m might be missing the obvious, but what is this about?

JMA thinks that the weak Typhoon Krosa is stronger than the C3 Typhoon Danas.

Genuinely baffling. No disrespect to forecasters but the cross-agency consistency in the WPac basin can be hard to follow sometimes. (See also Wipha, which afaik was never upgraded past 60 kts by JMA).

[cycloneye]

Now JTWC extends the typhoon status and new peak is 80kt.

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W IS FORECAST TO TRACK
POLEWARD THROUGH TAU 72 ALONG THE WESTERN PERIPHERY OF THE DEEP-
LAYERED STR TOWARD A BREAK IN THE STR MAINTAINED BY A SERIES OF
MIDLATITUDE SHORTWAVE TROUGHS. TS 12W WILL INTENSIFY OVER THE NEXT
24 HOURS TO A PEAK OF 75 KNOTS AS THE SYSTEM CONTINUES TO REMOISTEN
AND CONSOLIDATE WITH PERSISTENT CORE CONVECTION. HOWEVER, HIGH
NORTHERLY VERTICAL WIND SHEAR COULD CONTINUE TO HINDER MORE
SIGNIFICANT DEVELOPMENT. AFTER TAU 36, DRY AIR ENTRAINMENT IS
ANTICIPATED, WHICH WILL LIKELY LEAD TO A BRIEF PERIOD OF SLIGHT
WEAKENING. AFTER TAU 72, A STR WILL BUILD TO THE NORTH EFFECTIVELY
SLOWING THE POLEWARD PROGRESSION. CURRENTLY, THE SYSTEM IS EXPECTED TO
TURN NORTHEASTWARD. HOWEVER, THE EXACT TRACK MOTION IS UNCERTAIN DUE
TO COMPETING STEERING INFLUENCES THAT DEVELOP IN THE LATER FORECAST
PERIOD. THE SYSTEM IS FORECAST TO REACH ITS PEAK INTENSITY DURING THIS
EXTENDED PERIOD AS THE CORE REMOISTENS, VERTICAL WIND SHEAR DECREASES,
AND POLEWARD OUTFLOW IMPROVES INTO A DEEP MIDLATITUDE MAJOR SHORTWAVE
TROUGH TO THE NORTHEAST.

[cycloneye]

FORECAST DISCUSSION: TS 12W WILL CONTINUE TRACKING NORTHWARD ON THE
NEAR EQUATORIAL RIDGE TO THE EAST THROUGH TAU 48. THE STEERING
ENVIRONMENT WILL BECOME WEAK AND COMPETING BETWEEN THE NEAR
EQUATORIAL RIDGE AND A SUBTROPICAL RIDGE CENTERED OVER JAPAN. THE
NEAR EQUATORIAL RIDGE WILL REORIENT ON A SOUTHWEST-NORTHEAST RIDGE
AFTER TAU 72, ALLOWING THE SYSTEM TO DRIVE NORTHWESTWARD FOR THE
REMAINDER OF THE FORECAST PERIOD. THE SYSTEM WILL CONTINUE TO
COMBAT HIGHLY UNFAVORABLE VERTICAL WIND SHEAR WITH EXPANSIVE
DUAL-CHANNEL OUTFLOW FOR THE NEXT 24 HOURS. AFTER TAU 36, VERTICAL
WIND SHEAR WILL INCREASE UNFAVORABLY AND ENTRAIN DRY AIR INTO THE
CORE OF THE SYSTEM. THE QUASI-STATIONARY MOTION WILL DRAIN THE
OCEAN HEAT CONTENT AS WELL, BUT AFTER TAU 72 THE SYSTEM WILL MOVE
INTO WARMER FAVORABLE WATERS AND REINTENSIFY TO 80KTS BY THE END OF
THE FORECAST.

[cycloneye]

FORECAST DISCUSSION: TS 12W WILL CONTINUE TO TRACK NORTHWARD ON A
NEAR EQUATORIAL RIDGE (NER) TO THE EAST. THE SYSTEM WILL ENTER A
COMPETING STEERING ENVIRONMENT BETWEEN TAU 36-72 BETWEEN TWO
RIDGES, THE NEAR EQUATORIAL RIDGE TO THE SOUTHEAST AND THE
SUBTROPICAL RIDGE TO THE NORTHEAST. DURING THIS TIME PERIOD, THE
TRACK MOTION WILL BECOME IRREGULAR AND QUASI-STATIONARY. AFTER TAU
72, THE NEAR EQUATORIAL RIDGE TO THE SOUTHEAST WILL REORIENT ON A
SOUTHWEST-NORTHEAST AXIS, DRIVING THE SYSTEM NORTHEASTWARD FOR THE
REMAINDER OF THE FORECAST PERIOD. THE SYSTEM WILL SLIGHTLY WEAKEN
IN THE NEAR-TERM FORECAST AS THE SYSTEM CONTINUES TO REMAIN
PUMMELED BY THE UPPER-LEVEL TROUGH TO THE NORTHEAST. UPWELLING
BETWEEN TAU 36-72 WILL FURTHER RESULT IN WEAKENING DESPITE A CEASE
OF VERTICAL WIND SHEAR. REINTENSIFICATION IS ANTICIPATED TO OCCUR
AFTER TAU 72 AS THE SYSTEM MOVES INTO WARMER WATERS, LEADING TO AN
INTENSIFICATION OF 60KTS FOR THE REMAINDER OF THE FORECAST PERIOD.

[sasha_B]

Krosa has cleared out an eye (apparent on Himawari IR imagery) and ATCF now shows an intensity of 80 kts / 964 hPa for the 18z fix.

12W KROSA 250727 1800 24.4N 145.3E WPAC 80 964

[cycloneye]

[cycloneye]

Will get the most ACE at WPAC so far and has 3.6. The highest has been Danas with 5.2.

FORECAST DISCUSSION: TYPHOON (TY) 12W IS FORECAST TO TRACK NORTHWARD
TO NORTH-NORTHWESTWARD THROUGH TAU 48 ALONG THE WESTERN PERIPHERY OF
THE DEEP-LAYERED STR TOWARD A BREAK IN THE STR. TY 12W WILL INTENSIFY
OVER THE NEXT 24 HOURS TO A PEAK OF 90 KNOTS AS THE SYSTEM CONTINUES
TO CONSOLIDATE. AFTER TAU 24, THE STR IS FORECAST TO BUILD TO THE
NORTH, WHICH WILL RESULT IN A SIGNIFICANT DECREASE IN TRACK SPEEDS.
SLIGHT WEAKENING IS EXPECTED AFTER TAU 24 DUE TO DRY AIR ENTRAINMENT
AND EVENTUALLY UPWELLING COOL WATER, WHICH WILL WEAKEN THE SYSTEM AS
IT SLOWS FROM TAU 36 TO TAU 72. AFTER TAU 72, A MIDLATITUDE SHORTWAVE
TROUGH WILL DEEPEN TO THE NORTH ALLOWING TY 12W TO RESUME A POLEWARD
TRACK THROUGH TAU 120.

[cycloneye]

FORECAST DISCUSSION: TYPHOON (TY) 12W IS FORECAST TO TRACK
NORTH-NORTHWESTWARD TO NORTHWESTWARD THROUGH TAU 24 ALONG THE
WESTERN PERIPHERY OF THE DEEP-LAYERED STR TOWARD A BREAK IN THE
STR. TY 12W WILL MAINTAIN AN INTENSITY NEAR 75-80 KNOTS OVER THE
NEXT 24 HOURS. AFTER TAU 24, THE STR IS FORECAST TO BUILD TO THE
NORTH, WHICH WILL RESULT IN A SIGNIFICANT DECREASE IN TRACK SPEEDS.
SLIGHT WEAKENING IS EXPECTED AFTER TAU 12 DUE TO DRY AIR
ENTRAINMENT AND EVENTUALLY UPWELLING COOL WATER, WHICH WILL WEAKEN
THE SYSTEM AS IT SLOWS FROM TAU 24 TO TAU 48. AFTER TAU 48, A
MIDLATITUDE SHORTWAVE TROUGH WILL DEEPEN TO THE NORTH ALLOWING TY
12W TO RESUME A POLEWARD TRACK THROUGH TAU 120.

[ElectricStorm]

Looks like it's taking a huge hit from dry air. Probably well below typhoon status now and may take some time to recover but should have another round of intensification. ADT dropping fast

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 9.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 28 JUL 2025 Time : 040000 UTC
Lat : 26:41:24 N Lon : 144:38:59 E


CI# /Pressure/ Vmax
4.4 / 965.4mb/ 74.6kt


Final T# Adj T# Raw T#
3.5 3.4 2.4

[cycloneye]

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL
CLOUD BANDS AND FLARING CONVECTION WRAPPING INTO A LOW-LEVEL
CIRCULATION CENTER (LLCC) OVER TROPICAL STORM (TS) 12W. THE LLCC
HAS BECOME BROAD AS THE SYSTEM HAS WEAKENED OVER THE LAST SIX
HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
AN EARLIER 281200Z METOP-C ASCAT IMAGE REVEALING A BULLSEYE
LOW-LEVEL CIRCULATION CENTER. THE INITIAL INTENSITY OF 60 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED
SCATTEROMETRY AND THE FIXES LISTED BELOW. THE CONFIDENCE IS
SLIGHTLY DECREASED IN THE INTENSITY DUE TO A MAXIMUM OF 45KTS
REPRESENTED IN THE NORTHERN PERIPHERY OF THE AFOREMENTIONED
SCATTEROMETRY.

[wxman57]

1230 UTC ASCAT hit direction over Krosa indicated max wind 45 kts. It's not a typhoon.

[cycloneye]

Finnally JMA that is the oficial agency in that part of the world, downgrades KROSA to STS.

T2509(Krosa)
Issued at 2025/07/28 18:50 UTC
Analysis at 07/28 18 UTC
Grade STS
Scale -
Intensity -
Center position N27°30′ (27.5°)
E143°30′ (143.5°)
Direction and speed of movement WNW 10 km/h (6 kt)
Central pressure 975 hPa
Maximum sustained wind speed near center 30 m/s (60 kt)
Maximum wind gust speed 45 m/s (85 kt)
Radius of 50-kt wind area 110 km (60 NM)
Radius of 30-kt wind area E650 km (350 NM)
W330 km (180 NM)

[ElectricStorm]

Latest JTWC forecast gets this much closer to Tokyo now, consistent with latest model runs. Could be at or near typhoon strength by that time but the struggles of maintaining any significant convection continue. 50kts seems too high at the moment.

[cycloneye]

Still alive.


SUMMARY:
INITIAL POSITION: 29.0N 143.2E
INITIAL INTENSITY: 40 KTS
GEOGRAPHIC REFERENCE: 126 NM NORTH-NORTHEAST OF CHICHI JIMA
MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS WARMING
CLOUD TOPS AND FRAGMENTED CONVECTIVE BANDING OVER TROPICAL STORM
(TS) 12W. TROPICAL STORM (TS) 12W IS EMBEDDED WITHIN DRY AIR AND IS
FIGHTING TO MAINTAIN MOISTURE IN AN OTHERWISE MARGINAL ENVIRONMENT
FOR DEVELOPMENT. VERTICAL WIND SHEAR IS LOW AND FAVORABLE, AND AN
UPPER-LEVEL TROUGH TO THE NORTH IS ALLOWING MODERATE POLEWARD
OUTFLOW. SIGNIFICANT UPWELLING DUE TO THE QUASI-STATIONARY STATE
WHICH TS 12W HAS REMAINED IN IS ANOTHER NEGATIVE FACTOR WEIGHING
INTO THE DEGRADING STRUCTURE OF THE SYSTEM. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED RAGGED
CIRCULATION IDENTIFIED IN ANIMATED EIR. THE INITIAL POSITION IS
PLACED WITH LOW CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES
LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: COMPETING AND WEAK STEERING ENVIRONMENT


AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T3.0 - 45 KTS
RJTD: T3.0 - 45 KTS
RCTP: T3.0 - 45 KTS
KNES: T3.5 - 55 KTS
CIMSS SATCON: 44 KTS AT 301130Z
CIMSS ADT: 34 KTS AT 301130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
VWS: 5-10 KTS
SST: 27-28 CELSIUS
OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: LOW
INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 12W HAS REMAINED QUASI-STATIONARY OVER THE
LAST SIX HOURS, AND THE TRACK WILL REMAIN AND THE TRACK WILL REMAIN
IRREGULAR AND SLOW
WHILE IN A COMPETING STEERING ENVIRONMENT BETWEEN THE SUBTROPICAL
RIDGE OVER JAPAN AND MONSOONAL FLOW TO THE SOUTH. THE TRACK WILL
REMAIN SLOW AND IRREGULAR OVER THE NEXT 24 HOURS IN THE
NORTHWESTWARD DIRECTION. A VORTICITY MAXIMUM EMBEDDED WITHIN THE
MONSOON TROUGH TO THE SOUTHWEST WILL ENHANCE THE CURVE AS A RESULT
OF BINARY INTERACTION. AFTER TAU 48, THE SUBTROPICAL RIDGE
INFLUENCING THE SYSTEM WILL WEAKEN, AND TS 12W WILL CURVE
NORTHEASTWARD WITH THE MONSOONAL FLOW ON THE NORTHWESTERN PERIPHERY
OF THE NEAR EQUATORIAL RIDGE TO THE SOUTHWEST. TS 12W WILL STRUGGLE
TO INTENSIFY WHILE REMAINING QUASI STATIONARY AND SLOW FOR THE NEXT
24 HOURS DUE TO SIGNIFICANT UPWELLING. AS THE SYSTEM TRACKS
NORTHWESTWARD AFTER TAU 24, THE SYSTEM WILL BE MET WITH WARMER SEA
SURFACE TEMPERATURES, ALLOWING FOR GRADUAL INTENSIFICATION.
HOWEVER, THE UPPER-LEVEL ENVIRONMENT WILL BECOME UNFAVORABLE, AND
DRY AIR WILL CONTINUE TO INTRUDE INTO CYCLONE. VERTICAL WIND SHEAR
WILL INCREASE AFTER TAU 48, AND THE SYSTEM WILL CONTINUOUSLY WEAKEN
THROUGH THE END OF THE FORECAST