Advisories

WDPN32 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (KUJIRA) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 118.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 212 NM NORTHWEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A POORLY
ORGANIZED TROPICAL DEPRESSION WITH DEEP CONVECTION LIMITED TO THE
SOUTHWESTERN QUADRANT. MODERATE NORTHEASTERLY VERTICAL WIND SHEAR
IS ALSO APPARENT IN THE EIR, PRESSURING THE CONVECTION TO THE
SOUTHWEST AND PARTIALLY EXPOSING LOW-LEVEL CLOUDS ASSOCIATED WITH
THE LOW-LEVEL CIRCULATION CENTER. AN EARLIER 141339Z ASCAT-B PASS
REVEALED AN ELONGATED BUT CLOSED LLCC WITH THE HIGHEST WINDS IN THE
SOUTHEASTERN QUADRANT. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE WIND SPEED MINIMUM OBSERVED IN A 041740Z
AMSR-2 WIND SPEED PRODUCT AND EXTRAPOLATION FROM THE EARLIER ASCAT
DATA. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE SAME WIND SPEED PRODUCTS AND T1.0-2.0
AGENCY DVORAK FIXES. THE ENVIRONMENT IS CHARACTERIZED AS MARGINALLY
FAVORABLE WITH WARM SEA SURFACE TEMPERATURES BEING OFFSET BY WEAK
OUTFLOW ALOFT AND MODERATE VWS.

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

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT DOMINATED BY
LOW-LEVEL SOUTHWESTERLY MONSOON FLOW 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.0 - 25 KTS
   CIMSS D-PRINT: 25 KTS AT 041800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK 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 (TD) 13W (KUJIRA) HAS
REMAINED IN A QUASI-STATIONARY POSITION OVER THE PAST 6 HOURS AS IT
SLOWLY CONSOLIDATES. THE TRACK IS FORECAST TO REMAIN MOSTLY
QUASI-STATIONARY OVER THE NEXT 12 HOURS AS WEST-SOUTHWESTERLY
MONSOON FLOW FORCES TD 13W EASTWARD INTO LUZON. LANDFALL NEAR VIGAN
IS EXPECTED AROUND 051600Z. THE SYSTEM IS EXPECTED TO BRIEFLY REACH
TROPICAL STORM STATUS, AIDED BY THE SOUTHWEST MONSOON FLOW FUNNELED
BY THE WEST COAST OF LUZON. THE SYSTEM WILL RAPIDLY DECAY ONCE IT
MAKES LANDFALL AND IS EXPECTED TO DISSIPATE OVER LUZON.   

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ABOUT
THE EASTWARD MOTION OF THE SYSTEM OVER LUZON. THERE IS A DIVERGENCE
BETWEEN THE PHYSICS-BASED MODELS, WHICH DEPICT A FASTER TRACK
SPEED, AND EXPERIMENTAL AI MODELS, WHICH DEPICT A NOTABLY SLOWER
TRACK EASTWARD. THE JTWC TRACK FORECAST IS PLACED CLOSE TO, BUT
SLIGHTLY SLOWER THAN, THE MULTI-MODEL CONSENSUS WHICH ALIGNS CLOSER
TO THE PHYSICS-BASED SOLUTIONS. MODEL INTENSITY GUIDANCE IS IN
AGREEMENT ABOUT A SHORT TERM INTENSIFICATION FOLLOWED BY WEAKENING
OVER LAND. MOST GUIDANCE SUGGESTS A SECOND PERIOD OF INTENSIFICATION 
IF THE VORTEX SURVIVES PASSAGE OVER LUZON, HOWEVER, THIS IS ASSESSED 
TO BE AN UNLIKELY SCENARIO. THUS, THE JTWC INTENSITY FORECAST FOLLOWS 
THE MULTI-MODEL CONSENSUS THROUGH TAU 24, THEN DIPS BELOW THE GUIDANCE 
ENVELOPE DURING THE EXPECTED DECAY OVER LAND.

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