Tropical Storm ATSANI Advisory mar, 03-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W
(ATSANI) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 23W (ATSANI), LOCATED APPROXIMATELY 504
NM NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD
AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS A WEAK SYSTEM THAT HAS MAINTAINED AN OVERALL
POORLY-ORGANIZED CONVECTIVE STRUCTURE DISPLACED WESTWARD FROM A WEAK
AND RAGGED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS
PLACED WITH FAIR CONFIDENCE BASED ON THE PARTLY EXPOSED LLC IN THE
MSI LOOP AND IN MICROWAVE IMAGES INCLUDING THE 020510Z AMSR2 AND THE
020436Z ATMS IMAGES. THE INITIAL INTENSITY OF 25KTS IS BASED ON THE
WIND FIELD AROUND THE LLC IN THE 012345Z DIRECT ASCAT PASS AND
REFLECTS THE SUSTAINED 6-HR CONVECTIVE STRUCTURE. THE ENVIRONMENT IS
MARGINAL WITH MODERATE (20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK
OUTFLOW ALOFT OFFSET SLIGHTLY BY WARM (29-30C) SEA SURFACE
TEMPERATURES (SST) IN THE PHILIPPINE SEA. THE CYCLONE IS TRACKING
ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE
(STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TD 23W WILL TRACK MORE POLEWARD, AS IT ROUNDS THE WESTERN EDGE
OF THE STR, INTO A COL AREA SOUTH OF A SHORTWAVE MIDLATITUDE TROUGH
AND BETWEEN THE STEERING STR AND A SECONDARY STR TO THE NORTHWEST,
WHERE IT WILL REMAIN IN A QUASI-STATIONARY (QS) STATE UP TO TAU 48.
AFTERWARD, THE PRIMARY STR WILL BUILD AND SLOWLY DRIVE TD 23W WEST-
SOUTHWESTWARD AND OUT OF THE COL. THE ENVIRONMENT IS FORECAST TO
IMPROVE AS VWS WEAKENS AND POLEWARD OUTFLOW INCREASES, FUELING A
STEADY INTENSIFICATION TO 65KTS BY TAU 72. NUMERICAL MODELS DIVERGE
SIGNIFICANTLY WITH VARYING SOLUTIONS IN THE DURATION OF QS STATE IN
THE COL, LENDING LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST
TRACK.
   C. IN THE EXTENDED TAUS, THE PRIMARY STR WILL CONTINUE TO STEER TD
23W WEST-SOUTHWESTWARD IN THE PHILIPPINE SEA, THROUGH LUZON STRAIT,
AND INTO THE SOUTH CHINA SEA BY TAU 120. THE FAVORABLE ENVIRONMENT
CONDITIONS WILL PROMOTE FURTHER INTENSIFICATION TO A PEAK OF 75KTS BY
TAU 96. AFTERWARD, INCREASING VWS WILL WEAKEN THE SYSTEM TO 60KTS BY
TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 800 NM BY TAU
120 WITH NAVGEM AND UEMN SUGGESTING A RECURVATURE INTO JAPAN, LENDING
LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST.//
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