WDPN31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 31W (KALMAEGI) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.2N 137.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 68 NM NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 31W (KALMAEGI) WITH A SYMMETRIC CENTRAL DENSE OVERCAST
(CDO) OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE SYSTEM
IS RATHER COMPACT WITH THE CDO MEASURING ABOUT 190 NM IN DIAMETER.
A 011122Z METOP-B ASCAT IMAGE REVEALED AN ILL-DEFINED CENTER WITH
PRIMARILY 25-30 KNOT WINDS. A SMALL PATCH OF 35 KTS JUST NORTHWEST
OF THE ASSESSED CENTER WAS ANALYZED TO LIKELY BE RAIN CONTAMINATED,
KEEPING THE INITIAL INTENSITY ASSESSMENT OF 30 KTS IN LINE WITH THE
AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AMBIGUITIES VERSION OF THE SAME ASCAT IMAGE. ENVIRONMENTAL ANALYSIS
CONTINUES TO INDICATE THAT 31W IS IN A FAVORABLE ENVIRONMENT
CHARACTERIZED BY MODERATE RADIAL OUTFLOW ALOFT, LOW (5-10 KTS)
VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 31 KTS AT 011210Z
   CIMSS AIDT: 32 KTS AT 011210Z
   CIMSS D-PRINT: 29 KTS AT 011210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 31W IS FORECAST TO TRACK NORTHWESTWARD THROUGH
TAU 24, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR. AFTER TAU 24,
ANOTHER STR CENTERED SOUTHWEST OF TAIWAN WILL BUILD AND EXTEND
EASTWARD, CAUSING 31W TO TRACK WESTWARD AS IT APPROACHES THE
PHILIPPINES. 31W IS FORECAST TO MAKE LANDFALL BETWEEN TAU 48 AND 60
NEAR SOUTHERN SAMAR AND LEYTE. THE TRACK WILL THEN TURN MORE
WEST-NORTHWESTWARD FROM TAU 72 ONWARD AS THE SYSTEM TRAVERSES
THROUGH THE SOUTH CHINA SEA. REGARDING INTENSITY, 31W WILL REMAIN
IN A FAVORABLE ENVIRONMENT FOR FURTHER DEVELOPMENT THROUGH LANDFALL. 
THE CURRENT FORECAST CALLS FOR RAPID INTENSIFICATION (RI) FROM TAU 12 
TO 48 IN RESPONSE TO THE VERY WARM SEA SURFACE TEMPERATURES AND HIGH 
OHC VALUES THE SYSTEM WILL ENCOUNTER. THE INTENSIFICATION TREND WILL 
BRIEFLY COME TO A HALT AS THE SYSTEM TRACKS THROUGH THE VISAYAS, BUT 
THEN WILL CONTINUE AS THE SYSTEM TRACKS THROUGH THE SOUTH CHINA SEA 
AND HEADS TOWARD VIETNAM. EQUATORWARD OUTFLOW WILL GREATLY IMPROVE 
AND SEA SURFACE TEMPERATURES WILL REMAIN WARM, ALLOWING FOR 
INTENSIFICATION THROUGH THE END OF THE FORECAST PERIOD.


MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH TAU 72, WITH THE EXCEPTION OF NAVGEM WHICH TRACKS
THE VORTEX UP TOWARD LUZON, MUCH FURTHER NORTH THAN THE REMAINDER
OF GUIDANCE. DISCOUNTING NAVGEM, THERE IS A MERE 40 NM CROSS TRACK
SPREAD NEAR THE TIME OF LANDFALL AND A 70 NM CROSS-TRACK SPREAD AT
TAU 72. AFTER TAU 72, ALONG-TRACK SPREAD BEGINS TO INCREASE WITH
MODELS DIFFERING ON TRACK SPEEDS AFTER LANDFALL IN THE PHILIPPINES.
THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL
CONSENSUS (SLIGHTLY OFFSET DUE TO NAVGEM) WITH HIGH CONFIDENCE
THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE
CONTINUES TO BE IN POOR AGREEMENT WITH A 55 KNOT SPREAD NEAR THE
TIME OF LANDFALL. HAFS-A IS THE WEAKEST (60 KTS) WHILE COAMPS TC
(GFS BASED) IS THE STRONGEST (105 KTS). ALL MODELS AGREE ON
INTENSIFICATION ONCE THE VORTEX EMERGES WITHIN THE SOUTH CHINA SEA,
BUT WITH LARGE VARIATIONS IN RATE. OVERALL, THE JTWC INTENSITY
FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGHOUT THE FORECAST
WITH LOW CONFIDENCE. 

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