BoB: FOUR - Post-Tropical

[Subtrop]

95B INVEST 230730 1200 19.2N 89.8E IO 20 996

[ElectricStorm]

JTWC renumbers

04B FOUR 230731 1800 20.0N 92.0E IO 40 987

[cycloneye]

WDIO31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 04B (FOUR)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
INITIAL POSITION: 20.0N 92.0E
INITIAL INTENSITY: 40 KTS
GEOGRAPHIC REFERENCE: 138 NM SOUTH OF CHITTAGONG
MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS
SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPOSED BUT WELL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) JUST
WEST OF SITTWE, MYANMAR. THE FIRST HINTS OF THE ROTATION ARE ALSO
BECOMING EVIDENT IN THE ANIMATED RADAR DATA OUT OF BANGLADESH. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
EXPOSED LLCC IN THE EIR AND PROXY VISIBLE IMAGERY. WHILE AGENCY
DVORAK CURRENT INTENSITY FIXES ARE RELATIVELY LOW, IN THE T1.0 TO
T2.0 RANGE, TWO EARLIER ASCAT PASSES AT 311440Z AND 311528Z SHOWED
A WEDGE OF 35-40 KNOT WINDS ACROSS THE SOUTHERN HEMISPHERE OF THE
CIRCULATION, WITH THE HIGHEST WINDS IN THE SOUTHEAST QUADRANT. THE
SCATTEROMETER DATA LENT HIGH CONFIDENCE TO THE INTENSITY ESTIMATE,
WELL ABOVE THE DVORAK-BASED ESTIMATES. THE EIR ALSO SHOWS
DISORGANIZED CONVECTION DISPLACED AWAY FROM THE LLCC DUE TO
PERSISTENT LOW TO MODERATE NORTHEASTERLY SHEAR. BIT UPPER-LEVEL
WINDS ASSOCIATED THE TROPICAL EASTERLY JET (TEJ) APPEAR TO HAVE
WEAKENED JUST ENOUGH TO ALLOW FOR THE SYSTEM TO CONSOLIDATE AND
INTENSIFY. CONDITIONS ARE MARGINAL, WITH WARMS SSTS, AND GOOD
EQUATORWARD OUTFLOW OFFSET BY MODERATE TO HIGH NORTHEASTERLY SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF THE LOW TO
MID-LEVEL SUBTROPICAL RIDGE (STR) OVER CHINA.

AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.0 - 30 KTS
KNES: T1.5 - 25 KTS
DEMS: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
VWS: 20-25 KTS
SST: 29-30 CELSIUS
OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 04B (FOUR) WILL BE
SHORT-LIVED, AS IT TRACKS QUICKLY TO THE NORTH-NORTHWEST THROUGH
THE FORECAST PERIOD. LANDFALL IS CURRENTLY ANTICIPATED ON THE COAST
OF BANGLADESH WITHIN THE NEXT 24 HOURS, AND AFTER LANDFALL THE
SYSTEM WILL RAPIDLY MOVE INLAND TOWARDS THE VICINITY OF KOLKATA.
WHILE THE SYSTEM HAS ENJOYED A BRIEF PERIOD OF LOW TO MODERATE
SHEAR, WHICH ALLOWED IT TO INTENSIFY TO TC STRENGTH, ANOTHER PULSE
OF TEJ-ASSOCIATED NORTHEASTERLY FLOW WILL MOVE IN WITHIN THE NEXT
FEW HOURS AND SERVE TO SQUASH TC 04B AS IT TRACKS NORTHWARD.
HOWEVER, DUE TO ALREADY STRONG VORTICITY WHICH HAS DEVELOPED
INDEPENDENT OF ANY ORGANIZED CONVECTION, ENHANCED BY SOME
TERRAIN-INDUCED COMPRESSION ON THE EASTERN SIDE, THE SYSTEM WILL
LIKELY MAKE LANDFALL AS A 35 TO 40 KNOT TROPICAL CYCLONE. RAPID
WEAKENING AND DISSIPATION IS EXPECTED BY TAU 36 OVER SOUTHEAST
INDIA.

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT AGREEMENT ON A
NORTHWEST TRACK THROUGH LANDFALL, CURVING TO WESTWARD AFTER TAU 24,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. INTENSITY GUIDANCE IS
ALSO IN GOOD AGREEMENT THAT THE SYSTEM WILL MAINTAIN INTENSITY
THROUGH LANDFALL AND QUICKLY DISSIPATE THEREAFTER.

FORECAST CONFIDENCE:
TRACK 0 - 72 HR: HIGH
INTENSITY 0 - 72 HR: HIGH//
NNNN

[Sciencerocks]

[Sciencerocks]

[cycloneye]

The last warning that will be issued.

WTIO31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE 04B (FOUR) WARNING NR 003//
RMKS/
1. TROPICAL CYCLONE 04B (FOUR) WARNING NR 003
01 ACTIVE TROPICAL CYCLONE IN NORTHIO
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
010600Z --- NEAR 21.9N 90.4E
MOVEMENT PAST SIX HOURS - 310 DEGREES AT 16 KTS
POSITION ACCURATE TO WITHIN 025 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 035 KT, GUSTS 045 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATING AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
RADIUS OF 034 KT WINDS - 000 NM NORTHEAST QUADRANT
080 NM SOUTHEAST QUADRANT
070 NM SOUTHWEST QUADRANT
000 NM NORTHWEST QUADRANT
REPEAT POSIT: 21.9N 90.4E
---
FORECASTS:
12 HRS, VALID AT:
011800Z --- 23.0N 88.4E
MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
WIND RADII VALID OVER OPEN WATER ONLY
DISSIPATED AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND
---
REMARKS:
010900Z POSITION NEAR 22.2N 89.9E.
01AUG23. TROPICAL CYCLONE 04B (FOUR), LOCATED APPROXIMATELY 81 NM
WEST-SOUTHWEST OF CHITTAGONG, HAS TRACKED NORTHWESTWARD AT 16
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) TOGETHER WITH ANIMATED RADAR IMAGERY PROVIDED A
HIGH DEGREE OF CONFIDENCE TO THE INITAL LOCATION OF 04B. THE
FULLY EXPOSED CIRCULATION HAS VERY RECENTLY MADE LANDFALL OVER
SOUTHERN BANGLADESH AND IS FORECAST TO PROCEED INLAND, WHERE IT
WILL QUICKLY DISSIPATE BY TAU 12. NUMERICAL MODELS AND RELIABLE
MODEL INTENSITY GUIDANCE, BOTH ECHO THE JTWC TRACK AND
INTENSITY FORECASTS, LENDING HIGH CONFIDENCE TO BOTH. MINIMUM CENTRAL
PRESSURE AT 010600Z IS 990 MB.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.
MAXIMUM SIGNIFICANT WAVE HEIGHT AT 010600Z IS 15 FEET.//
NNNN

[Sciencerocks]

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