Tropical Storm PODUL Advisory 8月28日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (PODUL) WARNING NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 13W (PODUL), LOCATED APPROXIMATELY 109 NM
NORTH OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 19
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS A BROAD CIRCULATION WITH FLARING DEEP
CONVECTION NEAR THE CENTER AND SUSTAINED CONVECTION ALONG THE WESTERN
HALF OF THE CIRCULATION. THERE IS POOR CONFIDENCE IN THE INITIAL
POSITION BASED ON THE EIR AND LOCAL RADAR IMAGERY.  A 271241Z METOP-C
ASCAT PASS CAPTURED WINDS ALONG THE NORTHERN PERIPHERY TO SHOW A
BROAD AREA OF 25-30 KT WINDS AND A SMALL REGION OF 30-35 KT WINDS
ABOUT 140 NM NORTH OF THE CENTER. ALTHOUGH THIS PASS FAILED TO
CAPTURE THE LOW LEVEL CIRCULATION CENTER AND THE WESTERN PERIPHERY OF
THE SYSTEM, IT PROVIDES AN IDEA OF THE OVERALL WIND FIELD STRUCTURE.
THE CURRENT INTENSITY OF 35 KNOTS IS BASED ON MULTI-AGENCY DVORAK
ESTIMATES OF T2.0-T2.5 (30 KNOTS) AND THE AFOREMENTIONED ASCAT PASS.
THE ENVIRONMENT IS MARGINAL OVERALL WITH MODERATE TO STRONG (20-30
KT) VERTICAL WIND SHEAR (VWS) BEING OFFSET BY MODERATELY FAVORABLE
WESTWARD OUTFLOW AND WARM SEA SURFACE TEMPERATURE (29-30 CELSIUS). TS
13W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR).
3. FORECAST REASONING.
   A. THE JTWC TRACK HAS NOW SHIFTED TO THE SUSTAINED
WEST-NORTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST.
   B. THROUGH TAU 72, TS 13W SHOULD CONTINUE TO TRACK WESTWARD TO
WEST-NORTHWESTWARD AS IT PASSES SOUTH OF A COL WHILE A SHORTWAVE
TROUGH PASSES TO THE NORTH. AFTERWARDS, TS 13W WILL TRANSIT SOUTH OF
A SECOND STR CURRENTLY SITUATED OVER CHINA WITH A SECOND LANDFALL
ALONG SOUTHERN HAINAN AROUND TAU 72. THE SYSTEM WILL BE LIMITED BY
STRONG SHEAR AND POOR UPPER LEVEL DIVERGENCE, BUT TS 13W IS EXPECTED
TO GRADUALLY INTENSIFY TO 50 KTS BY TAU 48. THERE IS HIGH UNCERTAINTY
IN THE INTENSITY FORECAST DUE TO CONTINUED COMPETING ENVIRONMENTAL
INFLUENCES. DESPITE FAIR AGREEMENT IN THE MAJORITY OF THE MODEL
GUIDANCE, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC TRACK
FORECAST DUE TO HIGH UNCERTAINTY IN THE INITIAL POSITION.
   C. AFTER TAU 72, TS 13W IS EXPECTED TO CONTINUE TRACKING ALONG THE
SOUTHERN PERIPHERY OF THE STR. THE INTENSITY IS FORECAST TO WEAKEN
GRADUALLY DURING THIS PERIOD DUE TO LAND INTERACTION WITH VIETNAM AND
HAINAN, BUT UNCERTAINTY IN THE INTENSITY FORECAST IS HIGH AS THE
OUTFLOW MAY IMPROVE SIGNIFICANTLY DEPENDING ON THE TRACK ACROSS THE
SOUTH CHINA SEA. AVAILABLE DYNAMIC MODEL GUIDANCE IS IN POOR
AGREEMENT AS SOME MODELS DEPICT A SHARP POLEWARD TURN WHILE OTHERS
DEPICT A SUSTAINED WEST-NORTHWESTWARD TRACK. THE JTWC TRACK FORECAST
IS IN AGREEMENT WITH THE BULK OF THE MODEL GUIDANCE. BASED ON HIGH
UNCERTAINTY IN THE INFLUENCE OF THE APPROACHING SHORTWAVE TROUGH,
THERE IS LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST
TRACK.//
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