WPAC: NANMADOL - Post-Tropical

[euro6208]

WDPN31 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (NANMADOL)
WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 05W (NANMADOL), LOCATED APPROXIMATELY 140 NM
SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED NORTHEASTWARD AT 24 KNOTS
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY INDICATES A WEAKENING TREND WITH TIGHTLY-CURVED BANDING
WRAPPING INTO A RAGGED CENTER. THE INITIAL POSITION IS BASED ON A
TIGHT CLUSTER OF AGENCY FIXES THAT FITS IN THE CIRCULATION FEATURE ON
A COMPOSITE REFLECTIVITY RADAR LOOP FROM KYUSHU, JAPAN, WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 50 KNOTS BASED ON CONGRUENT
DVORAK ESTIMATES OF T3.5 FROM PGTW AND RJTD. UPPER-LEVEL ANALYSIS
INDICATES ROBUST POLEWARD OUTFLOW ENHANCED BY THE MIDLATITUDE
WESTERLIES TO THE NORTH. TS 05W IS NOW ACCELERATING POLEWARD ALONG
THE NORTHWESTERN EDGE OF THE DEEP SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS 05W IS FORECAST TO CONTINUE ACCELERATING NORTHEASTWARD
THROUGH AND WILL BEGIN INTERACTING WITH THE MIDLATITUDE WESTERLY
FLOW. THE SYSTEM WILL ALSO CONTINUE TO WEAKEN AS IT TRACKS OVER
COOLER SST (26 TO 25C) THEN DRAG ACROSS THE RUGGED TERRAIN OF KYUSHU,
SHIKOKU, AND HONSHU. AFTER TAU 24, TS NANMADOL WILL UNDERGO
EXTRA-TROPICAL TRANSITION (ETT). STRONG VERTICAL WIND SHEAR AND LAND
INTERACTION WILL SERVE TO SIGNIFICANTLY WEAKEN THE SYSTEM BEFORE IT
COMPLETES ETT BY TAU 36. THE DYNAMIC AIDS ARE IN VERY TIGHT AGREEMENT
LENDING HIGH
CONFIDENCE TO THE FORECAST TRACK.//
NNNN

[NotoSans]

MSLP recorded at Nagasaki was 991.6mb, which would support a central pressure of around 988mb at landfall. Using the KZC wind-pressure relationship would yield a landfall intensity of 50-55kt.

[NotoSans]

One interesting thing to note is that there seems to be a slight improvement in the overall structure before landfall.

[doomhaMwx]

Severe Tropical Storm Nanmadol(05W) has made landfall over Kyushu's Nagasaki Prefecture @ 8-9am JST this Tuesday...
This radar image from 11:40pm UTC (8:40am JST) shows the center over Nagasaki Prefecture...

[euro6208]

WDPN31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (NANMADOL)
WARNING NR 10//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL STORM (TS) 05W (NANMADOL), LOCATED APPROXIMATELY 111 NM
EAST-SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT
34 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED MULTISPECTRAL
SATELLITE IMAGERY SHOWS THE SYSTEM CONTINUING TO WEAKEN AND
ACCELERATE AS IT TRACKS ACROSS JAPAN AND INTERACTS WITH MID-
LATITUDE WESTERLIES. THE INITIAL POSITION IS BASED ON A LOW LEVEL
CIRCULATION VISIBLE ON JMA COMPOSITE REFLECTIVITY RADAR LOOP WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY OF 35 KNOTS IS BASED ON
SURFACE OBSERVATIONS TAKEN NEAR THE STORM. ENVIRONMENTAL ANALYSIS
INDICATES POLEWARD OUTFLOW IS BEING ENHANCED BY THE MID-LATITUDE
WESTERLIES TO THE NORTH, AND THE SYSTEM IS IN AN AREA OF MODERATE
VERTICAL WIND SHEAR. TS 05W IS TRACKING TO THE NORTHEAST AS IT IS
ROUNDING THE NORTHWEST PERIPHERY OF A SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
B. TS NANMADOL IS FORECAST TO CONTINUE ACCELERATING NORTHEASTWARD
UNDER THE INFLUENCE OF MID-LATITUDE WESTERLY FLOW. THE SYSTEM
WILL FURTHER WEAKEN DUE TO CONTINUED LAND INTERACTION AND MODERATE
TO STRONG VERTICAL WIND SHEAR. AFTER TAU 6, TS 05W WILL BEGIN EXTRA-
TROPICAL TRANSITION (ETT) AND COMPLETE ETT BY TAU 24. DYNAMIC MODEL
GUIDANCE REMAINS IN STRONG AGREEMENT LENDING HIGH CONFIDENCE TO THE
JTWC FORECAST TRACK.//
NNNN

[NotoSans]

Some more observations from Ishigakijima - a minimum sea level pressure of around 991mb was recorded at 01:10JST but the station never experienced a calm, suggesting that the central pressure was probably a few mbs lower. Nonetheless radar data and the wind shift suggested that the center passed very close to the station, probably skirting the southwestern edge of the island. I would say the central pressure was probably near 988mb at that time, which would support an intensity of around 60kt.

[euro6208]

I sense that JTWC might upgrade this postseason but low end 65 knots. Real intensity is likely Cat 2 to maybe Cat 3.

[doomhaMwx]

STS 1703 (Nanmadol)
Issued at 12:50 UTC, 4 July 2017

<Analysis at 12 UTC, 4 July>
Scale -
Intensity -
Center position N34°05' (34.1°)
E138°20' (138.3°)
Direction and speed of movement E 65 km/h (34 kt)
Central pressure 992 hPa
Maximum wind speed near center 25 m/s (50 kt)
Maximum wind gust speed 35 m/s (70 kt)
≥ 30 kt wind area S 220 km (120 NM)
N 110 km (60 NM)

[Alyono]

I sense that JTWC might upgrade this postseason but low end 65 knots. Real intensity is likely Cat 2 to maybe Cat 3.

stop hyping. This was in no way a cat 2 or 3

[Alyono]

JTWC has invented new meteorology

They have peak winds of a TROPICAL STORM at 35 kts

However, the system is moving at 37 kts

This represents a total lack of understanding of atmospheric dynamics. You CANNOT have a 35 kt TS that is moving at 37 kts. There CANNOT be a closed circulation in this setup.

This, to be brutally frank and honest, is a mistake you'd expect from a freshman undergrad, not a major TCWC

[senorpepr]

JMA maintains Nanmadol as a severe tropical storm, likely because of that fast forward motion as Alyono discussed.

WTPQ20 RJTD 041800
RSMC TROPICAL CYCLONE ADVISORY
NAME STS 1703 NANMADOL (1703)
ANALYSIS
PSTN 041800UTC 35.5N 142.6E FAIR
MOVE ENE 36KT
PRES 992HPA
MXWD 050KT
GUST 070KT
30KT 120NM SOUTH 60NM NORTH
FORECAST
24HF 051800UTC 39.3N 159.1E 80NM 70% EXTRATROPICAL LOW =

[euro6208]

WTPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/TROPICAL CYCLONE WARNING//
RMKS/
1. TROPICAL DEPRESSION 05W (NANMADOL) WARNING NR 012
DOWNGRADED FROM TROPICAL STORM 05W
01 ACTIVE TROPICAL CYCLONE IN NORTHWESTPAC
MAX SUSTAINED WINDS BASED ON ONE-MINUTE AVERAGE
WIND RADII VALID OVER OPEN WATER ONLY
---
WARNING POSITION:
041800Z --- NEAR 34.8N 142.4E
MOVEMENT PAST SIX HOURS - 080 DEGREES AT 31 KTS
POSITION ACCURATE TO WITHIN 020 NM
POSITION BASED ON CENTER LOCATED BY SATELLITE
PRESENT WIND DISTRIBUTION:
MAX SUSTAINED WINDS - 030 KT, GUSTS 040 KT
WIND RADII VALID OVER OPEN WATER ONLY
EXTRATROPICAL
REPEAT POSIT: 34.8N 142.4E
---
FORECASTS:
12 HRS, VALID AT:
050600Z --- 36.4N 150.5E
MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
WIND RADII VALID OVER OPEN WATER ONLY
EXTRATROPICAL
VECTOR TO 24 HR POSIT: 065 DEG/ 37 KTS
---
24 HRS, VALID AT:
051800Z --- 39.1N 159.3E
MAX SUSTAINED WINDS - 025 KT, GUSTS 035 KT
WIND RADII VALID OVER OPEN WATER ONLY
EXTRATROPICAL
---
REMARKS:
042100Z POSITION NEAR 35.2N 144.4E.
TROPICAL DEPRESSION 05W (NANMADOL), LOCATED APPROXIMATELY 136 NM
EAST-SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED EASTWARD AT 31
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY
SHOWS THE CONVECTION HAS SIGNIFICANTLY SHEARED FROM THE LOW LEVEL
CIRCULATION THAT HAS BECOME EMBEDDED IN THE COLD BAROCLINIC WIND
FIELD. REMNANTS OF TD NANMADOL HAS LOST TROPICAL CHARACTERISTICS AND
HAS FULLY TRANSITIONED INTO A COLD CORE SYSTEM. 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 041800Z IS 10 FEET.//
NNNN

[NotoSans]

Final advisory from the JMA.

WTPQ20 RJTD 050000
RSMC TROPICAL CYCLONE ADVISORY
NAME DEVELOPING LOW FORMER STS 1703 NANMADOL (1703)
ANALYSIS
PSTN 050000UTC 36N 146E
MOVE E 35KT
PRES 994HPA
MXWD 045KT
30KT 120NM SOUTH 60NM NORTH =