WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 02W (PENHA) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.3N 130.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 210 NM NORTH-NORTHWEST OF SONSOROL
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 02W (PENHA) AS A HEAVILY SHEARED LOW LEVEL CIRCULATION WITH
DEEP CONVECTION DISPLACED TO THE NORTHWEST. THE CIRCULATION
CURRENTLY HAS A LARGE WINDFIELD WITH STRONGER WRAPPING OVER THE
WESTERN SIDE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON ANIMATED EIR IMAGERY OF THE PARTIALLY EXPOSED LLCC WITH
DEEP CONVECTION CLOUDS BEING PUSHED NORTHWEST. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
OBJECTIVE AND SUBJECTIVE ESTIMATES LISTED BELOW. MODERATELY DRY AIR
PARTICULARLY VISIBLE THROUGHOUT THE SOUTHERN SEMICIRCLE OF THE
SYSTEM, AS WELL AS VERY WARM (29-30 C) SEA SURFACE TEMPERATURES
(SST) RESULT IN OVERALL MARGINAL ENVIRONMENTAL CONDITIONS.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED SOUTHEAST OF
TAIWAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 041800Z
   CIMSS ADT: 33 KTS AT 041900Z
   CIMSS AIDT: 33 KTS AT 041900Z
   CIMSS D-MINT: 33 KTS AT 041644Z
   CIMSS D-PRINT: 29 KTS AT 041900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TD PENHA WILL CONTINUE TO TRACK WEST TO
NORTHWESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE (STR) TO
THE SOUTHEAST OF TAIWAN. THOUGH THE CIRCULATION DOES NOT CURRENTLY
EXHIBIT STRONG SIGNS OF INTENSIFICATION, AN EXPECTED DROP IN
VERTICAL WIND SHEAR (10-15 KTS) AND DECREASE IN UPPER LEVEL
STEERING INFLUENCE WILL ALLOW A SHORT PERIOD OF INTENSIFICATION
OVER WARM SEA SURFACE TEMPERATURES JUST BEFORE LANDFALL OVER
MINDANAO BETWEEN TAU 12 AND TAU 24. TD PENHA WILL SLOW
SIGNIFICANTLY POST LANDFALL TRACKING WESTWARD OVER THE SULU SEA
TOWARDS PALAWAN, BUT TAKING OVER TWO DAYS TO GET THERE. MUCH OF
THIS FORECASTED TRACK CAN BE ATTRIBUTED TO THE WEAK STEERING
GRADIENT AND POOR VERTICAL STRUCTURE OF THE SYSTEM AS IT CROSSES
THE SULU SEA. SEA SURFACE TEMPERATURES WITHIN THE SULU SEA ARE
SLIGHTLY COOLER (27 C TO 28 C) AND SIGNIFICANTLY DRIER AIR FROM THE
WEST WILL IMPEDE FURTHER DEVELOPMENT KEEPING TD PENHA ON A STEADY
WEAKENING TREND UNTIL IT BECOMES ENGULFED IN THE COLD SURGE
BOUNDARY WEST OF THE PHILIPPINES BY TAU 96.

MODEL DISCUSSION: CROSS TRACK GUIDANCE IS SPREADING AMONGST THE
MODELS WITH JGSM COMMITTED TO A MORE WESTWARD TRACK OVER NORTHERN
PALAWAN WHILE NAVGEM IS AT THE EXTREME, RECURVING NORTHWARD. THE
SPREAD MEASURES AROUND 90 NM AT TAU 48. THE JTWC FORECASTED TRACK
IS PLACED CLOSE TO THE MULTI MODEL CONSENSUS UNTIL TAU 60. THE
TRACK SHIFTS SLIGHTLY SOUTH OF THE CONSENSUS ACCOUNTING FOR
UNCERTAINTY IN MODEL DEPICTION OF WEAKER STEERING AND FAVORING THE
WESTWARD MOVEMENT SLIGHTLY NORTH OF PALAWAN BEFORE ASSIMILATION
INTO COLD SURGE FLOW GIVEN THE CURRENT POOR STRUCTURE OF THE SYSTEM
AND FORECASTED COLD SURGE BOUNDARY IMPACTS. INTENSITY GUIDANCE ON
THE OTHER HAND CONCURS ON A BORDERLINE 30 KT TO 35 KT SYSTEM FOR
THE MAJORITY OF THE FORECAST WITH THE POSSIBILITY OF GAINING 40 KT
STRENGTH AROUND LANDFALL OVER MINDANAO.

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