Tropical Storm PHANFONE Advisory Mon Dec 23

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 30W (PHANFONE) WARNING NR
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 30W (PHANFONE), LOCATED APPROXIMATELY 717 NM
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT
18 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE LOW LEVEL CIRCULATION IS PARTIALLY OBSCURED BY
DEEP CONVECTION TO THE NORTHWEST. THERE IS FAIR CONFIDENCE IN THE
INITIAL POSITION BASED ON SHALLOW RAIN BANDS IN A 230634Z SSMI 85 GHZ
MICROWAVE IMAGE. THE INITIAL INTENSITY IS MAINTAINED AT 40KTS, BETWEEN
MULTI-AGENCY DVORAK ESTIMATES OF T2.5-T3.0 (35-45 KTS). MODERATE (20-25
KT) VERTICAL WIND SHEAR (VWS) IS PARTIALLY OFFSETTING GOOD POLEWARD
OUTFLOW AND WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE TO MAKE THE
ENVIRONMENT MARGINALLY SUPPORTIVE. TS 30W IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF A SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A.  THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 30W WILL TRACK GENERALLY WEST-NORTHWESTWARD THROUGHOUT THE
FORECAST. THE MARGINALLY FAVORABLE ENVIRONMENT WILL SUPPORT STEADY
INTENSIFICATION UNTIL LANDFALL AROUND TAU 30. AFTER LANDFALL, THE
PHILIPPINE ISLANDS WILL SLOW THE INTENSIFICATION RATE UNTIL TS 30W MOVES
OVER THE WARM WATERS OF THE SOUTH CHINA SEA (SCS). INITIALLY FAVORABLE
CONDITIONS IN THE SCS WILL ALLOW SOME MORE INTENSIFICATION THROUGH TAU
72.
   C. AFTER TAU 72, TS 30W WILL ENCOUNTER HIGH VWS AND RELATIVELY
COOLER, DRIER AIR. BY TAU 120, THE SYSTEM WILL WEAKEN TO 45KTS. THE JTWC
TRACK FORECAST FOLLOWS THE MODEL CONSENSUS SOLUTION UNTIL TAU 72.
AFTERWARD, THE FORECAST TRACK MORE CLOSELY FOLLOWS THE GFS/ECMWF
SOLUTIONS AS SOME OF THE OTHER MEMBERS TRACKS BECOME MORE ERRATIC.
DESPITE THE SLIGHT INCREASE IN UNCERTAINTY BEYOND TAU 72, THERE IS GOOD
CONFIDENCE IN THE JTWC TRACK FORECAST.//
NNNN
NNNN