WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 07W (SEVEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7N 127.2E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 380 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
ASYMMETRIC SYSTEM, WITH FLARING DEEP CONVECTION EXTENDING WELL TO
THE SOUTH ALONG THE EASTERN PERIPHERY OF THE CIRCULATION. A 041658Z
AMSR2 37GHZ AND COLORIZED 89GHZ MICROWAVE IMAGE SHOWED THE
ELONGATED CONVECTIVE BAND EXTENDING SOUTH, BUT ALSO INDICATED THE
DEVELOPMENT OF WEAK SPIRAL BANDING ON THE WESTERN AND SOUTHERN
PORTIONS OF THE LOW LEVEL CIRCULATION. THE INITIAL POSITION IS
PLACED JUST WEST OF THE FLARING CONVECTION WITH MODERATE CONFIDENCE
BASED ON THE AFOREMENTIONED AMSR2 PASS. THE INITIAL INTENSITY IS
SET AT 25 KNOTS, THOUGH A 041309Z ASCAT-B SHOWED THE PRESENCE OF 30
KNOT WINDS IN THE EASTERN THROUGH NORTHERN QUADRANTS OF THE LARGER
CIRCULATION. HOWEVER, WIND SPEEDS IN THE REMAINDER OF THE
CIRCULATION ARE BELOW 20 KNOTS, AND THUS, THE HIGHER WINDS ON THE
EASTERN PERIPHERY ARE NOT REPRESENTATIVE OF THE OVERALL INTENSITY
AT THIS TIME.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION 07W (SEVEN) WILL TRACK
NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STEERING
RIDGE THROUGH THE DURATION OF THE FORECAST PERIOD. THE SYSTEM IS
EXPECTED TO PASS THROUGH THE LUZON STRAIT WITHIN THE NEXT 24 HOURS
BEFORE TURNING SLIGHTLY MORE WEST-NORTHWESTERWARD AS LOW TO
MID-LEVEL RIDGING BUILDS IN TO THE NORTH ACROSS CENTRAL CHINA. SOME
MODELS ARE SUGGESTING THE SYSTEM WILL MAKE LANDFALL ALONG THE
SOUTHEAST COAST OF TAIWAN, BUT THE BUILDING OF THE LOW TO MID-LEVEL
RIDGE TO THE NORTH SHOULD KEEP THE TRACK OFFSHORE. THE SYSTEM IS
FORECAST TO MAKE LANDFALL ALONG THE COAST OF SOUTHEASTERN CHINA
NEAR TAU 60. OVER THE NEXT 12 TO 24 HOURS, IT IS EXPECTED THAT THE
LOW LEVEL VORTEX WILL CONTINUE TO TIGHTEN AND CONSOLIDATE, ENABLING
GENERATION AND MAINTENANCE OF DEEP CORE CONVECTION. AT THE SAME
TIME, VERY WARM (30-31C) SSTS, LOW (LESS THAN 10 KTS) VWS AND
RELATIVELY GOOD POLEWARD OUTFLOW ARE FORECAST TO CONTINUE,
RESULTING IN A PERIOD OF QUICK INTENSIFICATION THROUGH TAU 24.
AFTER CROSSING SOUTH OF TAIWAN, VWS IS EXPECTED TO INCREASE AND
OUTFLOW BECOME SLIGHTLY LESS FAVORABLE, WHICH WILL SLOW THE RATE OF
INTENSIFICATION, PEAKING AT 55 KNOTS BY TAU 36. AFTER LANDFALL THE
SYSTEM WILL RAPIDLY DISSIPATE DUE TO TERRAIN INTERACTION. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GENERAL AGREEMENT
ON THE OVERALL TRACK, BUT DOES SHOW A MODERATE DEGREE OF SPREAD.
SPREAD BETWEEN THE HWRF ON THE RIGHT, AND THE ECMWF ENSEMBLE ON THE
LEFT IS 120 NM AT TAU 24, INCREASING TO 360 NM BY TAU 48. ANALYSIS
OF THE GLOBAL MODEL FIELDS INDICATES THE HWRF, GFS ENSEMBLE AND
UKMET ENSEMBLE ARE UNREALISTICALLY RUNNING THE SYSTEM INTO AN
EXTENSION OF THE STR THAT BUILDS OVER CENTRAL CHINA, WHILE THE
REMAINDER OF THE CONSENUS MEMBERS REFLECT OR MORE LIKELY JOG
SLIGHTLY MORE WEST-NORTHWESTWARD IN RESPONSE TO THE STRENGTHENING
OF THE RIDGE. THE JTWC FORECAST TRACK LIES JUST TO THE EAST AND
SLIGHTLY SLOWER THAN THE MULTI-MODEL CONSENSUS TRACK THROUGH THE
DURATION OF THE FORECAST PERIOD, KEEPING THE TRACK OFFSHORE OF
TAIWAN AND THROUGH THE LUZON STRAIT. INTENSITY GUIDANCE MEMBERS ALL
AGREE ON INTENSIFICATION AND THE JTWC FORECAST IS CONSISTENT WITH
THE HWRF AND GFS SOLUTIONS, ABOVE THE MULTI-MODEL CONSENSUS.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM//
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