Tropical Storm TALIM Advisory Sun Jun 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 06W, LOCATED APPROXIMATELY 290 NM
SOUTH-SOUTHWEST OF HONG KONG, HAS TRACKED EAST-NORTHEASTWARD AT 07
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY SHOWS A LOW LEVEL CIRCULATION CENTER (LLCC) HAS
DEVELOPED ALONG THE NORTHERN EDGE OF A REGION OF STRONG GRADIENT
INDUCED WINDS OVER THE PAST 24 HOURS. DEEP CONVECTION HAS YET TO
BUILD OVER THE LLCC, BUT CONVECTION IS QUICKLY DEVELOPING NORTHWARD
FROM THE STRONG CONVERGENT REGION SOUTH OF THE LLCC INTO THE LLCC
ITSELF. UPPER LEVEL ANALYSIS INDICATES A WEAK MESOSCALE ANTICYCLONE
HAS STARTED BUILDING OVER THE LLCC, WITH MARGINAL VERTICAL WIND SHEAR
(VWS) (15-20 KNOTS), HELPING TO PROVIDE AMPLE EQUATORWARD OUTFLOW. AN
UPPER LEVEL SUBTROPICAL RIDGE (STR) IS BUILDING EASTWARD OVER
SOUTHERN CHINA AND IS BEGINNING TO MOVE INTO THE SOUTH CHINA SEA
(SCS) WHICH IS HAMPERING THE ANTICYCLONE FROM VENTING THE SYSTEM
POLEWARD. THE SYSTEM HAS BEEN QUASI-STATIONARY OVER THE PAST 48 HOURS
DUE TO A LACK OF STEERING INFLUENCES, HOWEVER TD 06W IS BEGINNING TO
TRACK WITH THE LOW LEVEL FLOW TO THE EAST-NORTHEAST. ADDITIONALLY, AS
TY 05W (GUCHOL) CONTINUES TRACKING POLEWARD, A STR IS EXPECTED TO
BECOME THE DOMINANT STEERING INFLUENCE. SEA SURFACE TEMPERATURES
(SSTS) THROUGHOUT THE SCS ARE FAVORABLE FOR FURTHER DEVELOPMENT. THE
INITIAL POSITION IS BASED ON THE EIR IMAGERY AND A WIDE SPREAD IN
FIXES FROM PGTW, KNES AND RJTD. THE CURRENT INTENSITY OF 30 KNOTS IS
BASED ON A 171315Z ASCAT PASS SHOWING WINDS NEAR 25 KNOTS, A 2.5/2.5
DVORAK ESTIMATE FROM PGTW AND A 2.0/2.0 FROM KNES AND RJTD.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 06W IS EXPECTED TO SLOWLY TRACK EASTWARD OVER THE NEXT 24
HOURS AS THE STR TO THE EAST CONTINUES BUILDING INTO THE SCS. DURING
THIS PERIOD FAVORABLE SSTS AND UPPER LEVEL OUTFLOW WILL ALLOW FOR TD
06W TO CONTINUE DEVELOPING. THE STR TO THE EAST WILL SLOWLY BUILD
ALLOWING FOR THE TRACK SPEED TO INCREASE BY TAU 36 THROUGH TAU 72,
TRACKING THE SYSTEM TO THE EAST-NORTHEAST THROUGH THE TAIWAN STRAIT.
THE TIMING FOR THE SYSTEM REMAINS QUESTIONABLE, BUT CURRENTLY THE
FORECAST HAS TD 06W TRACKING INTO THE STRAIT BY TAU 72. SSTS DROP OFF
MARKEDLY WITHIN THE STRAIT (26 CELSIUS) WHICH WILL LIKELY HINDER
STRONGER DEVELOPMENT. UPPER LEVEL SUPPORT WILL PERSIST THROUGH TAU
48, HOWEVER, PERSISTENT UPPER LEVEL TROUGHING OVER CONTINENTAL ASIA
WILL IMPACT TD 06W BETWEEN TAU 48 AND 72. THERE IS LOW CONFIDENCE
WITH THE FORECAST AS IT RELIES HEAVILY ON THE DEVELOPMENT OF THE STR,
AND IF THE TIMING IS NOT CORRECT, TD 06W WILL HAVE MORE TIME WITHIN
THE SCS TO INTENSIFY.
   C. IN THE EXTENDED FORECAST, TD 06W WILL CONTINUE TO TRACK ALONG
THE NORTHWESTERN PERIPHERY OF THE RE-ESTABLISHED STR TOWARDS
SOUTHWESTERN KYUSHU. DECREASING SSTS (22 TO 26 CELSIUS) AND
INCREASING VWS WILL NOT ALLOW FOR FURTHER DEVELOPMENT. HOWEVER, THERE
ARE INDICATIONS A WARM POOL OF WATER IS LOCATED TO THE NORTH OF
KADENA AB, OKINAWA WITH SSTS NEAR 29 CELSIUS. THE IMPACT THIS WILL
PROVIDE IN LIEU OF THE UNFAVORABLE UPPER LEVEL SUPPORT IS
QUESTIONABLE. THE POSSIBILITY EXISTS IT WILL ALLOW TD 06W TO REMAIN A
STRONG EXTRA-TROPICAL CIRCULATION AS EXTRA-TROPICAL TRANSITION BEGINS
AROUND TAU 96 AND COMPLETES BY TAU 120. AS WITH THE EARLY PORTION OF
THE FORECAST, CONFIDENCE IS LOW WITH THIS PERIOD OF THE FORECAST AS
THE IMPACTS OF THE STR STEERING INFLUENCE AND WHETHER THE WARM POOL
OF SSTS WILL BE A FACTOR FOR MAINTAINING TD 06W BETWEEN TAU 72 AND 96
ARE CURRENTLY IN QUESTION.//
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