WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (FENGSHEN) WARNING 
NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.6N 124.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 190 NM EAST-SOUTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SMALL
CORE OF DEEP CONVECTION EMBEDDED WITHIN A MUCH LARGER ROTATION
WITH
FRAGMENTED CONVECTIVE BANDS CONCENTRATED OVER THE WESTERN
HEMISPHERE (OVER THE PHILIPPINES). ANIMATED RADAR DATA FROM PAGASA
SUGGESTS A NASCENT LOW LEVEL CIRCULATION CENTER (LLCC) PASSING OFF
THE NORTHWEST COAST OF CATANDUANES AT 1200Z, WHILE A 181254Z
ASCAT-B PASS SHOWED A LIKELY LLCC OVER THE FAR SOUTHEASTERN TIP OF
LUZON, OR JUST OF OFFSHORE TO THE EAST. SURFACE OBSERVATIONS FROM
VIRAC WERE MISSING FOR SEVERAL HOURS, BUT A 181300Z OBSERVATION
SHOWED WINDS HAD SHIFTED FROM 070DEG TO 140DEG OVER THE PREVIOUS
THREE HOURS, HIGHLY SUGGESTIVE OF THE LLCC LYING SOMEWHERE TO THE
WEST OF THE STATION. THE LATEST FRAMES OF EIR AND RADAR SUGGEST
THE
LLCC IS NOW POSITIONED NORTH OF NAGA CITY, MOVING RAPIDLY TO THE
NORTHWEST. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE ANALYZES DESCRIBED ABOVE. THE INITIAL INTENSITY IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE INCREASING AGENCY
CURRENT INTENSITY ESTIMATES AND OBJECTIVE INTENSITY ESTIMATES
DESCRIBED BELOW. ENVIRONMENTAL CONDITIONS ARE FAVORABLE AND WOULD
BE HIGHLY FAVORABLE IF NOT FOR THE PROXIMITY TO LAND, WHICH IS
DISRUPTING DEVELOPMENT FOR THE MOMENT. ONCE THE SYSTEM MOVES AWAY
FROM LUZON AND APPROACHES THE WATERS AROUND THE PALILLO ISLANDS,
VERY WARM WATERS WITH HIGH OHC AWAIT, WHILE SHEAR REMAINS LOW AND
RADIAL OUTFLOW IS STRONG.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 39 KTS AT 181130Z
   CIMSS AIDT: 35 KTS AT 181130Z
   CIMSS D-MINT: 34 KTS AT 180929Z
   CIMSS D-PRINT: 30 KTS AT 181330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM (TS) 30W IS MOVING QUICKLY OFF
TO THE NORTHWEST, PARALLEL TO THE NORTHERN COAST OF SOUTHEASTERN
LUZON, ALONG THE SOUTHWESTERN SIDE OF A STRONG STR CENTERED FAR TO
THE NORTHEAST. OVER THE COURSE OF THE NEXT 12 TO 18 HOURS, TS 30W
WILL PASS CLOSE TO THE PALILLO ISLANDS AND MAKE LANDFALL ALONG THE
EASTERN COAST OF LUZON. AFTER MAKING LANDFALL, THE SYSTEM WILL
QUICKLY CROSS THE ISLAND, PASS THROUGH THE LINGAYEN GULF AND
EMERGE
INTO THE SOUTH CHINA SEA. ONCE BACK OVER WATER, THE SYSTEM WILL
CONTINUE TO TRACK NORTHWESTWARD AT A GOOD CLIP UNTIL TAU 48, WHEN
IT WILL SLAM HEAD FIRST INTO STRONG NORTHEASTERLY FLOW ASSOCIATED
WITH A COLD SURGE FUNNELING SOUTHWARD OUT OF THE TAIWAN STRAIT. IN
THE NEAR-TERM, AS THE SYSTEM MOVES AWAY FROM LAND AND INTO MORE
OPEN WATERS, IT IS EXPECTED TO RAPIDLY INTENSIFY, BUT THE PEAK
INTENSITY THE SYSTEM CAN REACH WILL BE LIMITED BY THE SHORT AMOUNT
OF TIME IT BEFORE MAKING LANDFALL. THE PEAK INTENSITY CAPTURED IN
THE FORECAST POINTS IS 45 KNOTS, BUT IT IS LIKELY THE SYSTEM WILL
REACH A SLIGHTLY HIGHER PEAK JUST PRIOR TO MAKING LANDFALL. AS THE
SYSTEM MOVES ACROSS THE RUGGED TERRAIN OF LUZON IT WILL WEAKEN
SIGNIFICANTLY, BUT QUICKLY REFORM ON THE WEST SIDE OF LUZON. ONCE
REESTABLISHED WEST OF THE PHILIPPINES, TS 30W WILL ONCE AGAIN
QUICKLY INTENSIFY UNDER FAVORABLE CONDITIONS, REACHING A PEAK OF
70
KNOTS BY TAU 72. AFTER TAU 48, THE SYSTEM WILL BEGIN TO SLOW DOWN
AND COULD EVEN BECOME QUASI-STATIONARY FOR A TIME AS IT MOVES INTO
A WEAK STEERING PATTERN, CAUGHT BETWEEN DEEP-LAYER RIDGING TO THE
EAST AND WEST, WHILE IN THE LOWER-LEVELS IT WILL BE PUSHING UP
AGAINST THE STRONG NORTHEASTERLY FLOW TRAPPED ALONG THE CHINESE
COAST. THE INFLUX OF RELATIVELY DRY AND STABLE AIR INTO THE
WESTERN
FLANK OF THE SYSTEM, ALONG WITH INCREASED SHEAR WILL BEGIN TO
WEAKEN THE SYSTEM IMMEDIATELY AFTER TAU 72. AS THE SYSTEM STEADILY
WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF THE
LOWER-LEVEL FLOW, AND PUSH SOUTHWESTWARD FROM TAU 72 THROUGH TAU
120. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD
CROSS-TRACK AGREEMENT TROUGH THE MAJORITY OF THE FORECAST PERIOD,
THOUGH THE NAVGEM DOES SEPARATE ITSELF FROM THE PACK AFTER TAU 72.
THROUGH TAU 72, THE GUIDANCE PACKAGE IS IN TIGHT AGREEMENT, WITH
JUST A 55NM SPREAD AT TAU 72. ALONG-TRACK UNCERTAINTY INCREASES
SHARPLY AFTER TAU 48 HOWEVER, WITH THE GFS BEING NOTABLY SLOWER
THAN THE REMAINDER OF THE GUIDANCE, LEADING TO A 100NM SPREAD BY
TAU 72. THROUGH TAU 120, CROSS-TRACK SPREAD INCREASES MODESTLY TO
120NM BETWEEN THE GOOGLE DEEP MIND ON THE NORTH SIDE AND THE ECMWF
ON THE SOUTH. ALONG-TRACK SPREAD ALSO INCREASES TO 135NM, NOT AS
MUCH AS MIGHT BE EXPECTED AS THE GFS CATCHES UP A BIT WITH THE
OTHER MODELS AFTER TAU 72. THE GEFS MEAN STILL SHOWS THE SYSTEM
MAKING LANDFALL ON THE VIETNAMESE COAST BY THE END OF THE FORECAST
PERIOD, BUT THE REMAINDER OF THE MODELS KEEP IT OFFSHORE. THE JTWC
FORECAST IS POSITIONED NEAR THE CONSENSUS MEAN THROUGH THE
FORECAST
PERIOD, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT WITH ALL GUIDANCE SUGGESTING NEAR-TERM INTENSIFICATION
TO
BETWEEN 40-45 KNOTS, FOLLOWED BY SOME WEAKENING AND THEN A STEADY
RAMP-UP TO A PEAK BETWEEN 60-75 KNOTS AT TAU 72. THE JTWC FORECAST
IS PLACED CLOSE TO THE HAFS-A THROUGH THE MAJORITY OF THE
FORECAST.
THE POST-LANDFALL INTENSITY OF 35 KNOTS HOWEVER IS BELOW ALL OF
THE
GUIDANCE, WHICH IS NOT SHOWING ANY SIGNIFICANT WEAKENING AS THE
SYSTEM CROSSES LUZON.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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