SOUTH INDIAN OCEAN: TC 27S(COURTNEY). 27/00UTC ESTIMATED LOCATON AND INTENSITY.
CURRENT INTENSITY IS 70 KNOTS CATEGORY 1 US: + 15 KNOTS OVER 24 HOURS
CLICK ON THE IMAGERY BELOW TO GET IT ANIMATED AND ENLARGED
26/2330UTC SATELLITE BULLETIN
TPXS11 PGTW 270028
A. TROPICAL CYCLONE 27S (COURTNEY)
B. 26/2330Z
C. 16.97S
D. 101.02E
E. FIVE/GK2A
F. T4.0/4.0/D0.5/24HRS STT: S0.0/03HRS
G. IR/EIR/VIS/MSI
H. REMARKS: 40A/PBO SBC/ANMTN. CNVCTN WRAPS .80 ON LOG10 SPIRAL
YIELDING A DT OF 3.5. MET YIELDS A 4.5. PT YIELDS A 4.0. DBO PT.
I. ADDITIONAL POSITIONS:
26/1837Z 17.38S 101.97E ATMS
TIMMERMAN
A. TROPICAL CYCLONE 27S (COURTNEY)
B. 26/2330Z
C. 16.97S
D. 101.02E
E. FIVE/GK2A
F. T4.0/4.0/D0.5/24HRS STT: S0.0/03HRS
G. IR/EIR/VIS/MSI
H. REMARKS: 40A/PBO SBC/ANMTN. CNVCTN WRAPS .80 ON LOG10 SPIRAL
YIELDING A DT OF 3.5. MET YIELDS A 4.5. PT YIELDS A 4.0. DBO PT.
I. ADDITIONAL POSITIONS:
26/1837Z 17.38S 101.97E ATMS
TIMMERMAN
WARNING 9 ISSUED AT 26/21UTC
WDXS31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 17.4S 102.2E
INITIAL INTENSITY: 70 KTS
GEOGRAPHIC REFERENCE: 438 NM SOUTHEAST OF THE COCOS ISLANDS
MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
SIGNIFICANT WAVE HEIGHT: 26 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27S (COURTNEY) WITH PERSISTENT DEEP CONVECTION
POSITIONED OVER AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC).
ALONG THE WESTERN FLANK, COLD-AIR STRATOCUMULUS FIELDS HAVE BEEN
OBSERVED WRAPPING INTO THE NORTHERN SEMICIRCLE. ALOFT, MODERATE
EQUATORWARD OUTFLOW HAS BEEN OBSERVED ON ANIMATED WATER VAPOR
IMAGERY, WITH VISIBLE CIRRIFORM FILAMENTS EXTENDING NORTHWARD, AND
A SECONDARY WEAK POLEWARD CHANNEL AS THE CYCLONE TRACKS ALONG THE
NORTHEASTERN EXTENT OF THE STR. RECENTLY, DEEP CONVECTION ON
ANIMATED SATELLITE IMAGERY HAS STARTED TO INDICATE FURTHER
INTENSIFICATION WITH UPPER-LEVEL RADIAL OUTFLOW BURSTING OUTWARD
FROM THE SYSTEMS VERTICAL STRUCTURE. ENVIRONMENTAL ANALYSIS SHOWS
THAT TC 27S REMAINS IN A FAVORABLE ENVIRONMENT, WITH LOW (10-15
KTS) VERTICAL WIND SHEAR (VWS), WARM (27-28 C) SEA SURFACE
TEMPERATURES (SST), AND A RELATIVELY MOIST CORE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED EIR
SATELLITE IMAGERY AND EXTRAPOLATION FROM EARLIER 261433Z METOP-C
ASCAT WIND DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON AGENCY DVORAK FIX ESTIMATES, CIMSS OBJECTIVE
INTENSITY ESTIMATES, AND THE AFOREMENTIONED METOP-C ASCAT WIND
DATA.
INITIAL WIND RADII BASIS: SAR DATA
CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T4.0 - 65 KTS
KNES: T4.0 - 65 KTS
DEMS: T4.0 - 65 KTS
APRF: T4.5 - 77 KTS
CIMSS SATCON: 59 KTS AT 261330Z
CIMSS ADT: 59 KTS AT 261900Z
CIMSS AIDT: 53 KTS AT 261900Z
CIMSS D-MINT: 56 KTS AT 261204Z
CIMSS D-PRINT: 59 KTS AT 261900Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
VWS: 10-15 KTS
SST: 27-28 CELSIUS
OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: MEDIUM
INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TC 27S IS FORECASTED TO TRACK WESTWARD ALONG
THE NORTHWESTERN EXTENT OF A DEEP-LAYER STR POSITIONED TO THE
SOUTHEAST THROUGH TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN ITS
SOUTHWESTWARD TRACK AROUND THE WESTERN PERIPHERY OF THE SAME
STEERING RIDGE. THE CYCLONE WILL CONTINUE ON A GENERALLY
SOUTHWESTWARD TRACK BETWEEN TAU 48 AND TAU 120, NEARING THE
SUBTROPICAL RIDGE AXIS AT THE END OF THE FORECAST PERIOD. WITH
REGARD TO INTENSITY, TC COURTNEY IS FORECASTED TO STEADILY
INTENSIFY UNTIL TAU 48 TO 90 KTS AS THE ENVIRONMENT REMAINS
FAVORABLE WITH WARM SST, LOW VWS, AND UPPER-LEVEL OUTFLOW SUPPORT.
AFTER TAU 48, THE CYCLONE WILL BEGIN ENCOUNTERING ENHANCED VWS OF
OVER 20 KTS AT THE SAME TIME THE SYSTEM NEARS THE 26C ISOTHERM
DIRECTLY TO THE SOUTH. WHILE THE SYSTEM ROUNDS THE WESTERN
PERIPHERY OF THE STR, THE MARGINAL ENVIRONMENT WILL BEGIN THE
INITIAL WEAKENING PHASE TO 80 KTS BY TAU 72, AND EVENTUALLY TO 55
KTS AT TAU 120 AS VWS ASSOCIATED THE EXPECTED MID-LATITUDE
INTERACTION INCREASES TO OVER 40 KTS AND CREATES A LARGELY
NON-CONDUCIVE ENVIRONMENT FOR FURTHER TC SUPPORT.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH REGARD TO THE TRACK OF TC 27S DURING THE INITIAL 72 HOURS OF THE
FORECAST PERIOD. THE CROSS-TRACK SPREAD REMAINS STEADY NEAR 60 NM
UNTIL TAU 48, WITH ALL JTWC CONSENSUS MEMBERS ILLUSTRATING A WESTWARD
TRACK. AFTER TAU 48, THE CROSS-TRACK DISTANCE SPREADS CONSIDERABLY,
EXTENDING TO 715 NM BY TAU 120. DUE TO THE UNCERTAINTY AFTER TAU 48,
THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE DURING THE
INITIAL 72 HOURS OF THE FORECAST PERIOD, AND LOW THEREAFTER.
UNFORTUNATELY, INTENSITY GUIDANCE HAS CONTINUED TO ILLUSTRATE
UNCERTAINTY THROUGHOUT THE ENTIRETY OF THE FORECAST PERIOD. GFS,
COAMPS-TC, AND HWRF REMAIN ON THE LOWER END OF INTENSITY ESTIMATES,
PEAKING AT 90 KTS NEAT TAU 72. ON THE UPPER END, HAFS-A REACHES A
MAXIMUM OF AROUND 120 KTS BETWEEN TAU 60 AND TAU 72. WITH THAT BEING
SAID, ECMWF ENSEMBLE SOLUTIONS CHARACTERIZE INTENSITIES BETWEEN 80-
100 KTS, WHILE GFS ENSEMBLE SOLUTIONS CONTINUE TO SHOW SUSTAINED
SURFACE INTENSITIES BETWEEN 40-60 KTS. THE JTWC INTENSITY FORECAST IS
PLACED WITH LOW CONFIDENCE THROUGH TAU 120 AND PLACED SLIGHTLY ABOVE
THE JTWC INTENSITY CONSENSUS AS THE ENVIRONMENT IS EXPECTED TO REMAIN
FAVORABLE UNTIL TAU 72, THEN BECOME NON-CONDUCIVE FOR FURTHER TC
SUPPORT BETWEEN TAU 72 AND TAU 120.
FORECAST CONFIDENCE:
TRACK 0 - 72 HR: HIGH
TRACK 72-120 HR: LOW
INTENSITY 0 - 72 HR: LOW
INTENSITY 72-120 HR: LOW//
NNNN
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 17.4S 102.2E
INITIAL INTENSITY: 70 KTS
GEOGRAPHIC REFERENCE: 438 NM SOUTHEAST OF THE COCOS ISLANDS
MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
SIGNIFICANT WAVE HEIGHT: 26 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27S (COURTNEY) WITH PERSISTENT DEEP CONVECTION
POSITIONED OVER AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC).
ALONG THE WESTERN FLANK, COLD-AIR STRATOCUMULUS FIELDS HAVE BEEN
OBSERVED WRAPPING INTO THE NORTHERN SEMICIRCLE. ALOFT, MODERATE
EQUATORWARD OUTFLOW HAS BEEN OBSERVED ON ANIMATED WATER VAPOR
IMAGERY, WITH VISIBLE CIRRIFORM FILAMENTS EXTENDING NORTHWARD, AND
A SECONDARY WEAK POLEWARD CHANNEL AS THE CYCLONE TRACKS ALONG THE
NORTHEASTERN EXTENT OF THE STR. RECENTLY, DEEP CONVECTION ON
ANIMATED SATELLITE IMAGERY HAS STARTED TO INDICATE FURTHER
INTENSIFICATION WITH UPPER-LEVEL RADIAL OUTFLOW BURSTING OUTWARD
FROM THE SYSTEMS VERTICAL STRUCTURE. ENVIRONMENTAL ANALYSIS SHOWS
THAT TC 27S REMAINS IN A FAVORABLE ENVIRONMENT, WITH LOW (10-15
KTS) VERTICAL WIND SHEAR (VWS), WARM (27-28 C) SEA SURFACE
TEMPERATURES (SST), AND A RELATIVELY MOIST CORE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED EIR
SATELLITE IMAGERY AND EXTRAPOLATION FROM EARLIER 261433Z METOP-C
ASCAT WIND DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON AGENCY DVORAK FIX ESTIMATES, CIMSS OBJECTIVE
INTENSITY ESTIMATES, AND THE AFOREMENTIONED METOP-C ASCAT WIND
DATA.
INITIAL WIND RADII BASIS: SAR DATA
CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T4.0 - 65 KTS
KNES: T4.0 - 65 KTS
DEMS: T4.0 - 65 KTS
APRF: T4.5 - 77 KTS
CIMSS SATCON: 59 KTS AT 261330Z
CIMSS ADT: 59 KTS AT 261900Z
CIMSS AIDT: 53 KTS AT 261900Z
CIMSS D-MINT: 56 KTS AT 261204Z
CIMSS D-PRINT: 59 KTS AT 261900Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
VWS: 10-15 KTS
SST: 27-28 CELSIUS
OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
ANALYSIS CONFIDENCE:
INITIAL POSITION: MEDIUM
INITIAL INTENSITY: MEDIUM
INITIAL WIND RADII: MEDIUM
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TC 27S IS FORECASTED TO TRACK WESTWARD ALONG
THE NORTHWESTERN EXTENT OF A DEEP-LAYER STR POSITIONED TO THE
SOUTHEAST THROUGH TAU 48. AFTER TAU 48, THE SYSTEM WILL BEGIN ITS
SOUTHWESTWARD TRACK AROUND THE WESTERN PERIPHERY OF THE SAME
STEERING RIDGE. THE CYCLONE WILL CONTINUE ON A GENERALLY
SOUTHWESTWARD TRACK BETWEEN TAU 48 AND TAU 120, NEARING THE
SUBTROPICAL RIDGE AXIS AT THE END OF THE FORECAST PERIOD. WITH
REGARD TO INTENSITY, TC COURTNEY IS FORECASTED TO STEADILY
INTENSIFY UNTIL TAU 48 TO 90 KTS AS THE ENVIRONMENT REMAINS
FAVORABLE WITH WARM SST, LOW VWS, AND UPPER-LEVEL OUTFLOW SUPPORT.
AFTER TAU 48, THE CYCLONE WILL BEGIN ENCOUNTERING ENHANCED VWS OF
OVER 20 KTS AT THE SAME TIME THE SYSTEM NEARS THE 26C ISOTHERM
DIRECTLY TO THE SOUTH. WHILE THE SYSTEM ROUNDS THE WESTERN
PERIPHERY OF THE STR, THE MARGINAL ENVIRONMENT WILL BEGIN THE
INITIAL WEAKENING PHASE TO 80 KTS BY TAU 72, AND EVENTUALLY TO 55
KTS AT TAU 120 AS VWS ASSOCIATED THE EXPECTED MID-LATITUDE
INTERACTION INCREASES TO OVER 40 KTS AND CREATES A LARGELY
NON-CONDUCIVE ENVIRONMENT FOR FURTHER TC SUPPORT.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
WITH REGARD TO THE TRACK OF TC 27S DURING THE INITIAL 72 HOURS OF THE
FORECAST PERIOD. THE CROSS-TRACK SPREAD REMAINS STEADY NEAR 60 NM
UNTIL TAU 48, WITH ALL JTWC CONSENSUS MEMBERS ILLUSTRATING A WESTWARD
TRACK. AFTER TAU 48, THE CROSS-TRACK DISTANCE SPREADS CONSIDERABLY,
EXTENDING TO 715 NM BY TAU 120. DUE TO THE UNCERTAINTY AFTER TAU 48,
THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE DURING THE
INITIAL 72 HOURS OF THE FORECAST PERIOD, AND LOW THEREAFTER.
UNFORTUNATELY, INTENSITY GUIDANCE HAS CONTINUED TO ILLUSTRATE
UNCERTAINTY THROUGHOUT THE ENTIRETY OF THE FORECAST PERIOD. GFS,
COAMPS-TC, AND HWRF REMAIN ON THE LOWER END OF INTENSITY ESTIMATES,
PEAKING AT 90 KTS NEAT TAU 72. ON THE UPPER END, HAFS-A REACHES A
MAXIMUM OF AROUND 120 KTS BETWEEN TAU 60 AND TAU 72. WITH THAT BEING
SAID, ECMWF ENSEMBLE SOLUTIONS CHARACTERIZE INTENSITIES BETWEEN 80-
100 KTS, WHILE GFS ENSEMBLE SOLUTIONS CONTINUE TO SHOW SUSTAINED
SURFACE INTENSITIES BETWEEN 40-60 KTS. THE JTWC INTENSITY FORECAST IS
PLACED WITH LOW CONFIDENCE THROUGH TAU 120 AND PLACED SLIGHTLY ABOVE
THE JTWC INTENSITY CONSENSUS AS THE ENVIRONMENT IS EXPECTED TO REMAIN
FAVORABLE UNTIL TAU 72, THEN BECOME NON-CONDUCIVE FOR FURTHER TC
SUPPORT BETWEEN TAU 72 AND TAU 120.
FORECAST CONFIDENCE:
TRACK 0 - 72 HR: HIGH
TRACK 72-120 HR: LOW
INTENSITY 0 - 72 HR: LOW
INTENSITY 72-120 HR: LOW//
NNNN
SOUTH INDIAN OCEAN/NORTHWEST AUSTRALIA: INVEST 93S. 27/00UTC ESTIMATED LOCATION AND INTENSITY
ADVISORY ISSUED AT 26/18UTC

THE AREA OF CONVECTION (INVEST 93S) PREVIOUSLY LOCATED NEAR 15.9S 121.1E IS NOW LOCATED NEAR 14.9S 121.0E, APPROXIMATELY 194 NM NORTH-NORTHWEST OF BROOME, AUSTRALIA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A POORLY ORGANIZED AREA OF FLARING CONVECTION OVER A VERY WEAKLY DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). ENVIRONMENTAL ANALYSIS DEPICTS FAVORABLE CONDITIONS FOR DUE TO LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, VERY WARM (30-31C) SEA SURFACE TEMPERATURES, AND A MODERATE EQUATORWARD OUTFLOW CHANNEL ALOFT. THE ECMWF ENSEMBLE IS CURRENTLY THE MOST AGGRESSIVE WITH GLOBAL DETERMINISTIC AND ENSEMBLE MODELS IN GOOD AGREEMENT ON A GENERALLY SOUTHWARD TRACK TOWARDS THE COAST OF AUSTRALIA OVER THE NEXT 24 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 23 TO 28 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.
26/2330UTC SATELLITE BULLETIN
TPXS10 PGTW 270015
A. TROPICAL DISTURBANCE 93S (NW OF BROOME)
B. 26/2330Z
C. 13.85S
D. 121.32E
E. FIVE/GK2A
F. T1.0/1.0 STT: S0.0/03HRS
G. IR/EIR/VIS/MSI
H. REMARKS: 49A/PBO PTLY XPSD LLCC/ANMTN. LOOSELY DEFINED CLOUD
LINES WITH OVERCAST LESS THAN 90NM ACROSS YIELD A DT OF 1.0. MET
AND PT AGREE. DBO DT.
I. ADDITIONAL POSITIONS: NONE
TIMMERMAN
A. TROPICAL DISTURBANCE 93S (NW OF BROOME)
B. 26/2330Z
C. 13.85S
D. 121.32E
E. FIVE/GK2A
F. T1.0/1.0 STT: S0.0/03HRS
G. IR/EIR/VIS/MSI
H. REMARKS: 49A/PBO PTLY XPSD LLCC/ANMTN. LOOSELY DEFINED CLOUD
LINES WITH OVERCAST LESS THAN 90NM ACROSS YIELD A DT OF 1.0. MET
AND PT AGREE. DBO DT.
I. ADDITIONAL POSITIONS: NONE
TIMMERMAN
WESTERN NORTH PACIFIC: INVEST 96S. 26/18UTC ESTIMATED LOCATION AND INTENSITY
Last Updated - 03/25/25 3 WEEK TROPICAL CYCLONE FORMATION PROBABILITY

GTH Outlook Discussion Last Updated - 03/25/25 Valid - 04/02/25 - 04/15/25 Based on RMM index observations, the Madden-Julian Oscillation (MJO) propagated rapidly east from the Indian Ocean to the Maritime Continent and West Pacific during mid to late March. Constructive interference between the MJO and the residual La Nina led to the strongest anomalous upper-level divergence over the Maritime Continent (120E) since November 2024. Anomalous upper-level convergence, located from South America eastward to Africa and the western Indian Ocean, is weaker due in part to a Kelvin wave crossing the Western Hemisphere. The dynamical RMM index forecasts feature large spread among GEFS and ECMWF ensemble members due to multiple modes of tropical variability (MJO, Kelvin waves, and La Nina) interact. However, a number of ensemble members, especially the GEFS, depict a continued eastward propagating MJO into the Western Hemisphere during the next two to three weeks. MJO precipitation composites for phases 7, 8, and 1 were considered in the weeks 2 and 3 GTH outlook, valid for April 2 to 15. Although the spatial extent of the suppressed convection recently decreased across the equatorial Central Pacific, a continued La Nina atmospheric response is expected through early April. During late March, Tropical Cyclone (TC) 27S developed across the southeastern Indian Ocean and is forecast to strengthen as it tracks westward according to the Joint Typhoon Warning Center (JTWC). Prior to the start of week-2, the GFS and ECMWF models are in good agreement that a TC forms near the Kimberley Coast of Australia. From April 2 to 8, enhanced convection coupled with anomalous low-level westerlies support a 20 to 40 percent chance of TC development from the Kimberley Coast east to the Gulf of Carpentaria. By week 3 (April 9 to 15), this elevated chance of TC genesis extends east to include the Coral Sea region. Elsewhere across the global tropics, early April is typically a very quiet time of year for tropical cyclones.

The precipitation outlook for weeks 2 (April 2-8) and 3 (April 9-15) is based on the historical skill weighted blend of the GEFS, CFS, and ECMWF along with considerations of MJO precipitation composites (phases 7, 8, and 1) and a lingering La Nina influence. Above-average precipitation is likely to persist across northern Australia through the first half of April, while above-average precipitation becomes more prevalent across the South Pacific. A gradual drying trend is expected for the Maritime Continent from weeks 2 to 3. During early to mid-April, northwestern South America is favored to remain wetter-than-average with below-normal precipitation more likely for portions of eastern Brazil.