WPAC: MERBOK - Post-Tropical

[1900hurricane]

Here's the 12Z Hong Kong sounding. Certainly not a saturated airmass.

[euro6208]

WDPN31 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MERBOK)
WARNING NR 03//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM 04W (MERBOK), LOCATED APPROXIMATELY 273 NM
SOUTH-SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHWESTWARD AT 10
KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
SHOWS A CONSOLIDATED SYSTEM WITH FLARING CONVECTION OVER THE LOW
LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS BASED ON THE
INFRARED LOOP AND AN 111104Z AMSU 89GHZ MICROWAVE IMAGE WHICH SHOWS
CONVECTIVE BANDING WRAPPING INTO THE CIRCULATION CENTER. THE INITIAL
INTENSITY OF 30 KNOTS IS BASED ON MULTI AGENCY DVORAK ESTIMATES
RANGING FROM T2.0 TO T2.5 AND AN 111314Z METOP-B ASCAT IMAGE SHOWING
35 KNOT WINDS IN THE EASTERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS
INDICATES CONTINUED FAVORABLE CONDITIONS FOR DEVELOPMENT WITH LOW
VERTICAL WIND SHEAR VALUES (10-15 KNOTS), STRONG EQUATORWARD
OUTFLOW, A STRONG VORTICITY SIGNATURE, AND VERY WARM SEA SURFACE
TEMPERATURES (30-31 C) ALONG THE FORECAST TRACK. TROPICAL STORM
(TS) 04W IS CURRENTLY TRACKING TO THE NORTHWEST ALONG THE WESTERN
PERIPHERY OF A SUB TROPICAL STEERING RIDGE.
3. FORECAST REASONING.
A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 04W IS FORECAST TO TRACK TO THE NORTHWEST ALONG THE WESTERN
PERIPHERY OF A SUBTROPICAL RIDGE (STR) UNTIL LANDFALL. THE SYSTEM IS
EXPECTED TO MAKE LANDFALL AFTER TAU 24 TO THE EAST OF HONG KONG. DUE
TO FAVORABLE CONDITIONS ALONG THE FORECAST TRACK PRIOR TO LANDFALL,
FURTHER INTENSIFICATION IS EXPECTED TO PEAK AT 40 KNOTS. AFTER TS
MERBOK MAKES LANDFALL IT WILL ROUND THE NORTHWESTERN EDGE OF THE STR
AND MOVE BACK OVER WATER IN THE EAST CHINA SEA. ONCE THE SYSTEM IS
OVER WATER IT WILL ACCELERATE NORTHEASTWARD AND GRADUALLY INTENSIFY
AS IT BEGINS THE EXTRA TROPICAL TRANSITION.
C. AFTER TAU 72, TS 04W WILL UNDERGO EXTRA TROPICAL TRANSITION AS
IT CONTINUES TO TRACK TO THE NORTHEAST. DYNAMIC MODEL GUIDANCE IS IN
STRONG AGREEMENT THAT THE SYSTEM WILL RECURVE TO THE EAST BUT WITH
GREATER SPREAD IN WHERE THE SYSTEM WILL MAKE LANDFALL AND HOW
RAPIDLY IT WILL TURN SINCE THE LAST FORECAST. THE PRINCIPAL OUTLIERS
OF THE TRACK GUIDANCE ARE COAMPS-TC AND NAVGEM WHICH HAVE THE SYSTEM
MAKING LANDFALL AT OR TO THE WEST OF HONG KONG RESPECTIVELY. THE
SPREAD IN TRACK LOCATION BY THE DYNAMIC MODEL GUIDANCE LENDS LOW
CONFIDENCE IN THE JTWC TRACK FORECAST.//
NNNN

[doomhaMwx]

The ASCAT Metop-B pass over it @ 6/11 13:12z shows 40-45kt winds near the center, specifically in the east...

[1900hurricane]

Appropriately, JMA is now at 40 kt. This may be about peak intensity though. The continental dry air and northeasterly shear do not look favorable up ahead.

Close
TS 1702 (Merbok)
Issued at 18:50 UTC, 11 June 2017

<Analysis at 18 UTC, 11 June>
Scale -
Intensity -
Center position N19°20' (19.3°)
E115°50' (115.8°)
Direction and speed of movement NNW 25 km/h (13 kt)
Central pressure 1000 hPa
Maximum wind speed near center 20 m/s (40 kt)
Maximum wind gust speed 30 m/s (60 kt)
≥ 30 kt wind area ALL 170 km (90 NM)

<Forecast for 06 UTC, 12 June>
Intensity -
Center position of probability circle N21°25' (21.4°)
E115°05' (115.1°)
Direction and speed of movement N 20 km/h (11 kt)
Central pressure 1000 hPa
Maximum wind speed near center 20 m/s (40 kt)
Maximum wind gust speed 30 m/s (60 kt)
Radius of probability circle 70 km (40 NM)

<Forecast for 18 UTC, 12 June>
Intensity -
Center position of probability circle N23°05' (23.1°)
E115°00' (115.0°)
Direction and speed of movement N 15 km/h (9 kt)
Central pressure 1002 hPa
Maximum wind speed near center 18 m/s (35 kt)
Maximum wind gust speed 25 m/s (50 kt)
Radius of probability circle 110 km (60 NM)

<Forecast for 18 UTC, 13 June>
Intensity -
TD
Center position of probability circle N26°05' (26.1°)
E120°00' (120.0°)
Direction and speed of movement ENE 25 km/h (14 kt)
Central pressure 1004 hPa
Radius of probability circle 280 km (150 NM)

[euro6208]

WDPN31 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MERBOK) WARNING NR
04//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 04W (MERBOK), LOCATED APPROXIMATELY 193 NM
SOUTH-SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHWESTWARD AT 14
KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM HAS BECOME MORE COMPACT BUT MAINTAINED CONVECTIVE
DEPTH AND WRAP. THE INITIAL POSITION IS BASED ON A TIGHT CLUSTER OF
WARM PIXELS IN THE CENTRAL DENSE OVERCAST WITH FAIR CONFIDENCE. THE
INITIAL INTENSITY OF 35 KNOTS IS BASED ON THE HIGH END OF MULTI
AGENCY DVORAK ESTIMATES RANGING FROM T2.0 TO T2.5. ENVIRONMENTAL
ANALYSIS INDICATES CONTINUED FAVORABLE CONDITIONS FOR DEVELOPMENT
WITH LOW VERTICAL WIND SHEAR (VWS), STRONG EQUATORWARD OUTFLOW, AND
VERY WARM SEA SURFACE TEMPERATURES (30-31 C). TS 04W IS CURRENTLY
TRACKING ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
A. THE FORECAST HAS BEEN CUT DOWN TO TAU 48 TO REFLECT DISSIPATION
OVER LAND. OTHERWISE, NO OTHER SIGNIFICANT CHANGE TO THE FORECAST
PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS MERBOK IS FORECAST TO MAKE LANDFALL AFTER TAU 12 TO THE
EAST OF HONG KONG AND TRACK NORTHWARD THEN NORTHEASTWARD OVER LAND AS
IT ROUNDS THE WESTERN EDGE OF THE STR. FAVORABLE CONDITIONS ALONG THE
FORECAST TRACK PRIOR TO LANDFALL WILL FUEL FURTHER INTENSIFICATION TO
A PEAK OF 40 KNOTS. AFTERWARD, INTERACTION WITH THE RUGGED TERRAIN OF
EASTERN CHINA, IN ADDITION TO INCREASED VWS WILL CAUSE RAPID EROSION
AND EVENTUAL DISSIPATION BY TAU 48. REMNANTS OF TS 04W WILL EXIT INTO
THE YELLOW SEA. THE DYNAMIC MODEL GUIDANCE HAS COME INTO TIGHTER
AGREEMENT IN THE NEAR AND MID TERM LENDING HIGH CONFIDENCE IN THE
JTWC TRACK FORECAST.//
NNNN

[1900hurricane]

The newest pass shows the mid-level center separated to the south of the low-level center by about a quarter degree due to shear, but honestly, Merbok is still organizing at a greater rate than my expectations thus far. I still feel like dry air will become an issue, but for the moment, it's confined to the west of the band to the west. Hong Kong, which is now east of that band, has shown considerable moistening in the lower and mid levels since the 12Z sounding. PWs are up over 0.5" and DCAPE is down over 750 J/kg in that 12 hour span.

[euro6208]

UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 8.2.1
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 12 JUN 2017 Time : 004000 UTC
Lat : 20:26:25 N Lon : 115:28:06 E


CI# /Pressure/ Vmax
3.0 / 993.6mb/ 45.0kt


Final T# Adj T# Raw T#
3.0 3.0 3.0

Center Temp : -54.0C Cloud Region Temp : -54.2C

Scene Type : UNIFORM CDO CLOUD REGION

Positioning Method : FORECAST INTERPOLATION

Ocean Basin : WEST PACIFIC
Dvorak CI > MSLP Conversion Used : CKZ Method

Tno/CI Rules : Constraint Limits : NO LIMIT
Weakening Flag : OFF
Rapid Dissipation Flag : OFF

C/K/Z MSLP Estimate Inputs :
- Average 34 knot radii : N/A
- Environmental MSLP : 1008mb

Satellite Name : HIM-8
Satellite Viewing Angle : 37.5 degrees

****************************************************

[euro6208]

TPPN10 PGTW 120025

A. TROPICAL STORM 04W (MERBOK)

B. 10/2350Z

C. 19.99N

D. 115.09E

E. FIVE/HMWRI8

F. T3.0/3.0/D1.5/24HRS STT: D0.5/03HRS

G. IR/EIR/VIS/MSI

H. REMARKS: 40A/PBO SBC/ANMTN. CNVCTN WRAPS .85 ON LOG10 SPIRAL
YIELDING A DT OF 3.5. MET IS 2.5. PT IS 3.0. DBO PT.

I. ADDITIONAL POSITIONS:
11/1848Z 19.65N 115.27E SSMI


LEMBKE

[Yellow Evan]

TPPN10 PGTW 120025

A. TROPICAL STORM 04W (MERBOK)

B. 10/2350Z

C. 19.99N

D. 115.09E

E. FIVE/HMWRI8

F. T3.0/3.0/D1.5/24HRS STT: D0.5/03HRS

G. IR/EIR/VIS/MSI

H. REMARKS: 40A/PBO SBC/ANMTN. CNVCTN WRAPS .85 ON LOG10 SPIRAL
YIELDING A DT OF 3.5. MET IS 2.5. PT IS 3.0. DBO PT.

I. ADDITIONAL POSITIONS:
11/1848Z 19.65N 115.27E SSMI


LEMBKE

Given DT of 3.5, might be worth going 50 here.

[1900hurricane]

For what it's worth, the 00Z Haikou sounding looks fairly similar to the 12Z Hong Kong sounding, so the dry air is still hanging around, but as I mentioned, it's confined to the outside of the western band.

[1900hurricane]

TPPN10 PGTW 120025

A. TROPICAL STORM 04W (MERBOK)

B. 10/2350Z

C. 19.99N

D. 115.09E

E. FIVE/HMWRI8

F. T3.0/3.0/D1.5/24HRS STT: D0.5/03HRS

G. IR/EIR/VIS/MSI

H. REMARKS: 40A/PBO SBC/ANMTN. CNVCTN WRAPS .85 ON LOG10 SPIRAL
YIELDING A DT OF 3.5. MET IS 2.5. PT IS 3.0. DBO PT.

I. ADDITIONAL POSITIONS:
11/1848Z 19.65N 115.27E SSMI


LEMBKE

Given DT of 3.5, might be worth going 50 here.

I'd tend to agree based on the latest microwave pass.

[Yellow Evan]

Aaaaaaaaaand JTWC lets me down...

WP, 04, 2017061200, , BEST, 0, 204N, 1150E, 40, 994, TS, 34, NEQ, 55, 50, 45, 40, 1005, 125, 50, 0, 0, W, 0, , 0, 0, MERBOK, S,

[euro6208]

WDPN31 PGTW 120300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MERBOK)
WARNING NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 04W (MERBOK), LOCATED APPROXIMATELY 122 NM
SOUTH-SOUTHEAST OF HONG KONG, HAS TRACKED NORTH-NORTHWESTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY
SHOWS THE SYSTEM HAS MAINTAINED CONVECTIVE DEPTH AS FEEDER BANDS
WRAPPED TIGHTER INTO THE CIRCULATION CENTER. THE INITIAL POSITION IS
BASED ON A LOW REFLECTIVITY CIRCULATION FEATURE IN THE 112252Z SSMIS
MICROWAVE PASS WITH FAIR CONFIDENCE. THE INITIAL INTENSITY OF 40
KNOTS IS BASED ON AN OVERALL ASSESSMENT OF SATCON AND AGENCY DVORAK
ESTIMATES RANGING FROM T2.5 TO T3.0. ENVIRONMENTAL ANALYSIS INDICATES
CONTINUED FAVORABLE CONDITIONS FOR DEVELOPMENT WITH LOW VERTICAL WIND
SHEAR (VWS), STRONG EQUATORWARD OUTFLOW, AND VERY WARM SEA SURFACE
TEMPERATURES (30-31 C). TS 04W IS CURRENTLY TRACKING ALONG THE
WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS MERBOK IS FORECAST TO MAKE LANDFALL SHORTLY AFTER TAU 12
JUST TO THE EAST OF HONG KONG AND TRACK NORTHWARD THEN NORTHEASTWARD
OVER LAND AS IT ROUNDS THE WESTERN EDGE OF THE STR. FAVORABLE
CONDITIONS WILL FUEL SLIGHT INTENSIFICATION TO A PEAK OF 45 KNOTS
PRIOR TO LANDFALL. AFTERWARD, INTERACTION WITH THE RUGGED TERRAIN OF
EASTERN CHINA, IN ADDITION TO INCREASED VWS WILL CAUSE RAPID EROSION
AND EVENTUAL DISSIPATION BY TAU 48. THE REMNANTS OF TS 04W WILL EXIT
INTO THE YELLOW SEA WITH A VERY SMALL CHANCE FOR RE-INTENSIFICATION.
THE DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT IN THE NEAR
AND MID TERM LENDING HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.//
NNNN

[doomhaMwx]

Another nice ASCAT pass showed a couple of 50kt wind flags in Merbok's eastern semicircle...
Strongest winds are confined in the eastern semicircle, where most of its rainbands are found, while the circulation's western half appears to be even lacking TS-force winds, which may be a relief for areas(including HongKong) that are west of the expected landfall location...

[1900hurricane]

Looks like the shear/dry air combo is starting to take its toll on Merbok.

[NotoSans]

Looks like Merbok is going to make landfall over Hong Kong in the next few hours. It would be the first TC since Nuri in 2008 to do so.

[euro6208]

Waglan Island just outside of Hong Kong reporting 60 mph gusting to 70 mph at this moment...

[doomhaMwx]

JMA upgraded it into a Severe TS @ 12z...

[1900hurricane]

12Z Hong Kong sounding features a nearly saturated profile up to 400 mb with lapse rates approximately that of the moist adiabat. Pretty tropical, but typical for locations within a tropical cyclone circulation. Drier air above that can be attributed to the upper level shearing winds.

[doomhaMwx]

Merbok has made landfall over Mirs peninsula according to the HKO, just to the east of HongKong, at around 11pm HKT...