WPAC: 24W - Tropical Depression

[mrbagyo]

92W INVEST 180821 1200 22.0N 118.0E WPAC 15 997

[euro6208]

AN AREA OF CONVECTION (INVEST 92W) HAS PERSISTED NEAR
22.0N 118.0E, APPROXIMATELY 262 NM SOUTHWEST OF TAIPEI. A RECENT
ASCAT METOP-A PASS DEPICTS A CLOSED, WELL-DEFINED LOW LEVEL
CIRCULATION WITH A LARGE SWATH OF 20 KNOT WINDS TO THE SOUTHERN
SECTOR. INFRARED IMAGERY SHOWS THE CIRCULATION AS FULLY EXPOSED WITH
SPARSE DEEP CONVECTION TO THE SOUTH. UPPER LEVEL ANALYSIS INDICATES
A MODERATE ENVIRONMENT WITH LOW VERTICAL WIND SHEAR (5-10KT), BUT
VERY LITTLE DIVERGENCE. SEA SURFACE TEMPERATURES ARE FAVORABLE AT 28-
30C. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT THE CIRCULATION WILL
GRADUALLY INTENSIFY AS IT MOVES NORTHEAST. MAXIMUM SUSTAINED SURFACE
WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 997 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.

[mrbagyo]

Now a Tropical Depression per JMA

TROPICAL DEPRESSION 998 HPA AT 22N 119E ALMOST STATIONARY.

[doomhaMwx]

REMARKS:
THE AREA OF CONVECTION (INVEST 92W) PREVIOUSLY LOCATED
NEAR 22.4N 119.0E, IS NOW LOCATED NEAR 22.1N 119.0E, APPROXIMATELY
224 NM SOUTHWEST OF TAIPEI, TAIWAN. ANIMATED MULTISPECTRAL IMAGERY
DEPICTS AN ELONGATED LOW LEVEL CIRCULATION WITH WEAK, FLARING
CONVECTION WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC). A
220158Z METOP-A ASCAT PASS SHOWS A DEFINED SURFACE CIRCULATION WITH
THE STRONGEST WINDS DISPLACED TO THE EAST. A 220158Z MHS METOP-A
IMAGE REVEALS FLARING DEEP CONVECTION, ALSO DISPLACED TO THE EAST OF
THE LLCC. THE ENVIRONMENT IS FAVORABLE FOR DEVELOPMENT WITH LOW TO
MODERATE VERTICAL WIND SHEAR (10-20 KTS), GOOD DIVERGENCE ALOFT, AND
WARM SURFACE TEMPERATURES OF 28-30C. DEVELOPMENT OF THE SYSTEM IS
DEPENDENT UPON ITS INTERACTION WITH THE ROUGH TERRAIN OF TAIWAN. THE
LONGER THAT THE SYSTEM REMAINS QUASI-STATIONARY IN THE SOUTH CHINA
SEA, THE GREATER ITS CHANCES ARE OF CONSOLIDATING INTO A TROPICAL
DEPRESSION. HOWEVER, IF THE SYSTEM REACHES TAIWAN BEFORE FURTHER
CONSOLIDATION, THE LAND INTERACTION WILL REDUCE THE LIKELIHOOD OF
IMMEDIATE DEVELOPMENT BEFORE THE SYSTEM REEMERGES NORTH OF TAIWAN.
REGARDLESS, 30+ KNOT WINDS ARE EXPECTED IN THE LUZON STRAIT DUE TO
TERRAIN FUNNELING AS THE CIRCULATION PASSES OVER TAIWAN. MAXIMUM
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 18 TO 23 KNOTS. MINIMUM SEA
LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1007 MB. THE POTENTIAL FOR
THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24
HOURS IS HIGH.

[mrbagyo]

Over land

[NotoSans]

Despite being overland, this system seems to have continued to consolidate. Surface observations suggest that this may now be a tropical storm, but the agencies usually won’t do such upgrade overland. The western part of Taiwan is mostly flat, which may be a reason why the system has not weakened.

This is going to be a major rain threat to the southwestern part of Taiwan as well as the system remains quasi-stationary.

[mrbagyo]

Several locations have now recorded 400mm+ accumulated precipitation.





I would guess PW in Southern Taiwan is in the range of 2.5 to 3.0 inch

[mrbagyo]

The rainfall dropped by this TD to Kaohsiung today has far exceeded the monthly mean rainfall for August which is about 416.7 mm

Some areas in Kaohsiung are now at 500mm level.

[NotoSans]

JTWC upgrades to TD 24W.

[euro6208]

[euro6208]

WDPN32 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 24W (TWENTYFOUR)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 24W (TWENTYFOUR), LOCATED APPROXIMATELY 57 NM
WEST-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED EAST-NORTHEASTWARD
AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED MULTI-
SPECTRAL SATELLITE IMAGERY DEPICTS AN EXPOSED LOW LEVEL CIRCULATION
CENTER WITH CONVECTION SHEARED TO THE SOUTH. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MULTI-SPECTRAL
IMAGERY AND SUPPORTED BY THE TAIWAN COMPOSITE RADAR LOOP. THE
CURRENT INTENSITY ASSESSMENT OF 30 KNOTS IS BASED ON A 230217Z ASCAT
PASS SHOWING ISOLATED 30 KT WIND BARBS TO THE NORTH. UPPER-LEVEL
ANALYSIS SHOWS THE SYSTEM HAS DEVELOPED AN EQUATORWARD OUTFLOW
CHANNEL AND IS TRACKING THROUGH WARM SSTS (27-28 C), ALLOWING IT TO
INTENSIFY SLIGHTLY, ALTHOUGH TERRAIN INTERACTION WITH TAIWAN AND
MODERATE (15-20 KT) WIND SHEAR IS LIMITING ITS INTENSIFICATION
POTENTIAL. TD 24W HAS MOVED SLOWLY TO THE NORTHEAST UNDER A COMPLEX
STEERING ENVIRONMENT CONSISTING OF A NEAR EQUATORIAL RIDGE (NER) TO
THE SOUTH, A SUB-TROPICAL RIDGE (STR) TO THE NORTHEAST, AND
MESOSCALE TERRAIN EFFECTS FROM THE MOUNTAINS OF TAIWAN.
3. FORECAST REASONING.
A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TD 24W IS FORECAST TO TRACK NORTHWESTWARD IN A WEAK STEERING
ENVIRONMENT THROUGH TAU 12. AFTER TAU 12, THE STR TO THE NORTHEAST
BUILDS AND CAUSES THE TRACK DIRECTION TO SHIFT WESTWARD AND THE
STORM MOTION TO ACCELERATE. THE MARGINALLY FAVORABLE ENVIRONMENT OF
WARM SSTS AND EQUATORWARD OUTFLOW BUT MODERATE VERTICAL WIND SHEAR
AND LAND CLOSE BY, WILL ALLOW 24W TO MAINTAIN ITS 30 KT INTENSITY
THROUGH MAKING LANDFALL IN CHINA AT TAU 24. ONCE THE SYSTEM MAKES
LANDFALL, THE FRICTIONAL EFFECTS OF TERRAIN INTERACTION WILL RAPIDLY
WEAKEN THE SYSTEM AND LEAD TO DISSIPATION BY TAU 36. AVAILABLE
DYNAMIC MODEL GUIDANCE VARIES ON THE DEPICTION OF WHEN 23W WILL TURN
WESTWARD AS THE STR BUILDS TO ITS EAST, WITH HWRF THE EASTERN
OUTLIER SHOWING CONTINUED ALBEIT SLOW NORTHEASTWARD MOTION, AND
NAVGEM AND GFS SHOWING A SHARP IMMEDIATE TURN TO THE WEST. DUE TO
THE SIGNIFICANT SPREAD IN MODEL GUIDANCE, THERE IS OVERALL LOW
CONFIDENCE IN THE JTWC FORECAST TRACK.//
NNNN

[euro6208]

WTPN32 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
RMKS/
1. TROPICAL DEPRESSION 24W (TWENTYFOUR) WARNING NR 007
01 ACTIVE TROPICAL CYCLONE IN NORTHWESTPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
250600Z --- NEAR 24.7N 117.7E
MOVEMENT PAST SIX HOURS - 265 DEGREES AT 16 KTS
POSITION ACCURATE TO WITHIN 040 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
REPEAT POSIT: 24.7N 117.7E
---
FORECASTS:
12 HRS, VALID AT:
251800Z --- 24.3N 116.2E
MAX SUSTAINED WINDS - 020 KT, GUSTS 030 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
VECTOR TO 24 HR POSIT: 255 DEG/ 07 KTS
---
24 HRS, VALID AT:
260600Z --- 24.0N 114.8E
MAX SUSTAINED WINDS - 020 KT, GUSTS 030 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
---
REMARKS:
250900Z POSITION NEAR 24.6N 117.3E.
TROPICAL DEPRESSION 24W (TWENTYFOUR), LOCATED APPROXIMATELY 208
NM WEST OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 16 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A WEAK LLCC NEARLY DEVOID OF CONVECTION, WITH DISSIPATING
CONVECTIVE BANDS SHEARED FAR TO THE SOUTH. THE INITIAL POSITION IS
OVER LAND, BASED WITH HIGH CONFIDENCE ON THE MSI LOOP. THE CURRENT
INTENSITY IS ASSESSED AT 25 KNOTS BASED THE OVERALL RAGGED
APPEARANCE, SURFACE OBSERVATIONS ALONG THE COAST SHOWING 999 MB,
WHICH WOULD SUPPORT 25 KT WINDS. THE SYSTEM WILL TRACK WESTWARD
UNDER A BUILDING STR TO THE NORTHEAST, AND DISSIPATE DUE TO
FRICTIONAL EFFECTS OVER LAND. MOST MODELS AND THE MULTI-MODEL
CONSENSUS DEPICT THE SYSTEM CONTINUING TO MOVE WEST-SOUTHWESTWARD
AND DISSIPATING IN THE NEXT TWELVE HOURS DUE TO LAND INTERACTION.
HWRF IS THE EXCEPTION, WHICH DEPICTS A RECURVE TO THE NORTHEAST IN
THE TRACK AFTER TAU 36. THE OFFICIAL JTWC FORECAST TRACK LIES CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. 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.//
NNNN