BoB: FOUR - Post-Tropical

[Subtrop]

IO, 99, 2022081712, , BEST, 0, 180N, 950E, 15, 999, DB, 0, , 0, 0, 0, 0, 0, 0, 0, 0, 0, B, 0, , 0, 0, INVEST, ,

[doomhaMwx]

TCFA

WTIO21 PGTW 180900

REMARKS:
THE AREA OF CONVECTION (INVEST 99B) PREVIOUSLY LOCATED NEAR 18.9N 93.4E IS
NOW LOCATED NEAR 19.5N 92.2E, APPROXIMATELY 169 NM SOUTH OF CHITTAGONG, BANGLADESH.
ENHANCED INFRARED SATELLITE IMAGERY DEPICTS AN EXPOSED, TIGHTLY WRAPPED LOW LEVEL
CIRCULATION CENTER WITH DEEP CONVECTIVE BANDING ALONG THE WESTERN PERIPHERY WRAPPING
INTO THE SOUTHEASTERN PERIPHERY. A 180359Z ASCAT-B BULLSEYE PASS REVEALS WIND SPEEDS OF
UP TO 35KTS IN SOUTHERN PERIPHERY. ENVIRONMENTAL ANALYSIS INDICATES FAVORABLE
CONDITIONS FOR DEVELOPMENT CHARACTERIZED BY ROBUST WESTWARD UPPER LEVEL OUTFLOW IN
ASSOCIATION WITH THE TEJ, A SMALL POCKET OF LOW TO MODERATE (10-20 KTS) VERTICAL WIND
SHEAR (VWS) AND WARM (29-30C) SEA SURFACE TEMPERATURES. NUMERICAL MODEL GUIDANCE
INDICATES THAT INVEST 99B WILL TRACK WEST-NORTHWESTWARD TOWARD KOLKATA AND MAKE
LANDFALL WITHIN THE NEXT 36-48 HOURS. INVEST 99B IS EXPECTED TO PEAK IN INTENSITY
WITHIN THE NEXT 24-36 HOURS JUST BEFORE MAKING LANDFALL. INVEST 99B IS EXPECTED TO
TRACK INTO AN AREA OF LOWER VWS ALLOWING THE SYSTEM TO FURTHER INTENSIFY. MAXIMUM
SUSTAINED SURFACE WINDS ARE ESTIMATED AT 28 TO 33 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 994 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT
TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS HIGH.

[cycloneye]

 https://twitter.com/philklotzbach/status/1560373564896817153

[doomhaMwx]

WDIO31 PGTW 182100
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: 20.5N 89.9E
INITIAL INTENSITY: 35 KTS
GEOGRAPHIC REFERENCE: 151 NM SOUTHEAST OF KOLKATA, INDIA
MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MASS
OF BUILDING CONVECTION OVER AN ASSESSED LOW LEVEL CIRCULATION (LLC)
TRACKING WEST-NORTHWEST OVER THE NORTHERN BAY OF BENGAL. AN 181859Z
37 GHZ GMI PASS INDICATES AN CONSOLIDATING SYSTEM WITH FRAGMENTED
BANDING WRAPPING INTO THE CENTER OF THE LLC IN THE NORTHEAST AND
SOUTHWEST QUADRANTS. THIS PASS ALSO INDICATES A MAJORITY OF THE
CONVECTIVE ACTIVITY TO BE IN THE SOUTHERN PERIPHERY. ENVIRONMENTAL
ANALYSIS INDICATES TC 04B IS IN A MARGINAL AREA FOR FURTHER
DEVELOPMENT WITH STRONG UPPER LEVEL OUTFLOW, A HIGH MAGNITUDE 850 MB
SIGNATURE, AND WARM (29-30 C) SEA SURFACE TEMPERATURES, OFFSET BY
STRONG (25-30 KTS) VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON MULTIPLE AGENCY FIXES,
PARTIAL RADAR IMAGERY FROM KOLKATA, INDIA AND THE AFOREMENTIONED
EIR DATA. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON PGTW DVORAK ESTIMATE, SET SLIGHTLY HIGHER THAN
KNES AND DEMS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA FROM 180359Z.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.5 - 35 KTS
KNES: T2.0 - 30 KTS
DEMS: T1.0 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
VWS: 25-30 KTS
SST: 28-29 CELSIUS
OUTFLOW: STRONG WESTWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04B IS ON A DIRECT PATH TO MAKE LANDFALL 74
NM TO THE SOUTHWEST OF KOLKATA ALONG THE COAST OF NORTHEAST INDIA.
THE INTENSITY WILL STEADILY INCREASE TO 45 KNOTS BY TAU 12 AS THE
VERTICAL WIND SHEAR IS EXPECTED TO DECREASE DUE TO A BREAK IN THE
UPPER LEVEL WINDS OVER THE NEXT 24 HOURS. THE INTENSITY IS EXPECTED
TO REACH A MAXIMUM OF 50 KNOTS JUST BEFORE LANDFALL DUE TO THE
OVERALL IMPROVEMENT OF THE ENVIRONMENT AS THE SYSTEM TRACKS
WEST-NORTHWEST. BY TAU 24 TC 04B WILL DECREASE IN INTENSITY TO 40
KNOTS AND BEGIN DISSIPATION DUE TO LAND INTERACTION AFTER LANDFALL.
BY TAU 36 THE SYSTEM WILL BE DISSIPATED WITH THE INTENSITY FALLING
TO 30 KNOTS.

MODEL DISCUSSION: THE JTWC TRACK CONSENSUS ENVELOPE IS RELATIVELY
TIGHT WITH A GRADUAL SPREAD TO 27 NM BY TAU 12, DECREASING TO 14 NM
AFTER LANDFALL BY TAU 24. DUE TO THIS TIGHT ENVELOPE THE CONFIDENCE
IN THE JTWC FORECAST TRACK IS HIGH. INTENSITY GUIDANCE IS IN RATHER
GOOD AGREEMENT WITH A 10-15 KNOT SPREAD AT TAU 12, WITH HWRF AND
COAMPS-TC BEING THE MOST AGGRESSIVE. THIS COUPLED WITH THE IMPROVING
ENVIRONMENT OVER THE NEXT 24 HOURS LENDS MEDIUM CONFIDENCE IN THE
JTWC INTENSITY FORECAST WHICH IS SET SLIGHTLY HIGHER THAN CONSENSUS.

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

[doomhaMwx]

Monsoon depressions are common over BoB in August but rarely get organized enough to meet JTWC and IMD ≥34kt warning in this basin. The back-to-back formation of 03A last week and now 04B is a rare feat in the NIO in August. Both TCs are still within the climatological norm with regards to genesis location though.

[wxman57]

Officially, this is not a TC, it's just a low pressure area. JTWC is not an official agency. I agree, though, it's a TC. ASCAT indicated 35kt winds 24 hours ago.

[doomhaMwx]

IMD 00Z.

Sub: Depression over northwest & adjoining northeast Bay of Bengal

Yesterday’s Low Pressure Area over northeast and adjoining areas of eastcentral Bay of Bengal,
Bangladesh & Myanmar coasts moved northwestwards concentrated into a Depression and lay
centered 0530 hrs IST of today, the 19th August 2022, over northwest & adjoining northeast Bay of
Bengal near latitude 20.5°N and longitude 89.7°E, about 310 km east-southeast of Balasore
(Odisha), 250 km east-southeast of Digha (West Bengal) and 210 km east-southeast of Sagar
Islands.

It is very likely to move west-northwestwards and intensify into a Deep Depression during next 06
hours. Continuing to move in the same direction. It is likely to cross West Bengal and Odisha coast
between Balasore & Sagar Islands around evening of today the 19th August, 2022. After landfall it
would continue to move west-northwestwards across north Odisha, West Bengal and Jharkhand
towards north Chhattisgarh and weaken gradually.

[doomhaMwx]

04B FOUR 220819 1200 21.7N 88.2E IO 40 994
04B FOUR 220819 0600 21.2N 88.9E IO 45 990
04B FOUR 220819 0000 20.7N 89.5E IO 40 991

 https://twitter.com/Indiametdept/status/1560551504372977664

[doomhaMwx]

Satellite and radar show that TS 04B is making landfall over India's West Bengal state. An AWS in Kakdwip, South 24 Parganas recorded a min sea-level pressure of 985mb at 12:15Z. TS-force winds are probably confined south of the center as no station has recorded TS-force winds so far.

[doomhaMwx]

Remains pretty organized well inland over India ~36hrs after it made landfall (IMD still calls it a deep depression). The moist monsoonal environment at this time of the year helps sustain these systems over land.