21W still a weak tropical depression

Météo974

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WESTERN NORTH PACIFIC

TD 21W
As of 18:00 UTC Oct 16, 2019:
Location: 17.9°N 129.9°E
Maximum Winds: 25 kt ( 45km/h)
Minimum Central Pressure: 1004 mb
WDPN31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE)
WARNING NR 002//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 21W (TWENTYONE), LOCATED APPROXIMATELY
532 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED
WEST-NORTHWESTWARD AT 06 KNOTS (KTS) OVER THE PAST SIX HOURS.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS FLARING
CONVECTION LOCATED OVER A DEVELOPING LOW LEVEL CIRCULATION (LLC). THE
MAJORITY OF THE ASSOCIATED CONVECTION IS LOCATED IN THE NORTHEAST
QUADRANT OF THE SYSTEM WITH SOME CONVECTIVE BANDING, SUPPORTED BY
161838Z SSMI 37GHZ MICROWAVE IMAGE. THE INITIAL POSITION IS PLACED
WITH FAIR CONFIDENCE BASED ON EIR AND THE AFOREMENTIONED MICROWAVE
IMAGE. THE INITIAL INTENSITY IS SET AT 25 KTS BASED ON THE WIND FIELD
OBSERVED IN THE 161204Z ASCAT-C IMAGE AND DVORAK CURRENT INTENSITY
(CI) ESTIMATES OF T1.5/25 KTS FROM PGTW AND RJTD. TD 21W IS
TRANSITING THROUGH AN AREA OF LOW (10-15 KTS) VERTICAL WIND SHEAR
(VWS) WITH GOOD POLEWARD AND EQUATORWARD OUTFLOW. SEA SURFACE
TEMPERATURES (SST) ARE FAVORABLE AT 28-29 CELSIUS. TD 21W IS TRACKING
ALONG THE SOUTHERN PERIPHERY OF THE LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. UNDER THE STEERING INFLUENCE OF THE AFOREMENTIONED STR, TD 21W
WILL TRACK WEST-NORTHWESTWARD THEN WESTWARD THROUGH TAU 36.
AFTERWARDS, INTERACTION WITH A NORTHEAST SURGE EVENT IS EXPECTED TO
TURN THE SYSTEM WEST-SOUTHWESTWARD. UPPER LEVEL DIVERGENCE IS
SLIGHTLY OFFSET TO THE NORTHEAST AND WILL SLOWLY DECREASE OVER THE
NEXT 36-48 HOURS. THUS, TD 21W IS FORECAST TO HAVE A BRIEF PERIOD FOR
INTENSIFICATION TO 30 KNOTS PRIOR TO GRADUALLY DISSIPATING AS IT
INTERACTS WITH THE NORTHEAST SURGE AND TERRAIN ON LUZON. MODEL
GUIDANCE IS LIMITED TO AEMN, ECMWF AND NVGM DUE TO THE WEAK NATURE OF
THIS SYSTEM. MODELS ARE IN GOOD AGREEMENT WITH NVGM AS THE
SOUTHERNMOST OUTLIER, LENDING TO HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK.//
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