Tropical Storm SON-TINH Advisory Sa, 27-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (SON-TINH) WARNING
NR 11//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 24W (SON-TINH), LOCATED APPROXIMATELY 415 NM
EAST-SOUTHEAST OF HUE, VIETNAM, HAS TRACKED WESTWARD AT 13 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS TIGHTLY-CURVED CONVECTIVE BANDING WRAPPING INTO THE
SOUTHEAST QUADRANT OF A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC). AS DEPICTED IN MSI AS WELL AS A 260527Z AMSU IMAGE,
DEEP CONVECTIVE BANDING IS FRAGMENTED OVER THE NORTHERN SEMI-CIRCLE.
MSI ALSO SHOWS AN AREA OF STRATOCUMULUS (SC) OVER THE NORTHERN
PERIPHERY OF THE LLCC AND NUMEROUS SURFACE OBSERVATIONS WITHIN THE
SC FIELD INDICATE RELATIVELY COOLER, DRIER AIR WITH DEW POINTS
RANGING FROM 20 TO 21C AND SLP VALUES NEAR 1011MB. AN UPPER-AIR
SOUNDING FROM XISHA-DAO, APPROXIMATELY 170NM NORTHWEST OF THE
CURRENT CENTER, SHOWS SOME DRY AIR IN THE MID-LEVELS, WHICH MAY BE
HINDERING CONVECTIVE DEVELOPMENT OVER THE NORTHERN SEMI-CIRCLE.
HOWEVER, THE TOTAL PRECIPITABLE WATER IMAGERY REVEALS A DEEP, MOIST
ENVELOPE ASSOCIATED WITH THE SYSTEM. THERE IS GOOD CONFIDENCE IN THE
INITIAL POSITION BASED ON THE MSI AND THE AMSU IMAGE. THE INITIAL
INTENSITY IS ASSESSED AT 55 KNOTS BASED ON DVORAK ESTIMATES OF 55
KNOTS FROM ALL AGENCIES. UPPER-LEVEL ANALYSIS CONTINUES TO DEPICT A
FAVORABLE ENVIRONMENT WITH GOOD OUTFLOW AND WEAK VERTICAL WIND
SHEAR. THE 26/00Z 500MB ANALYSIS DEPICTS AN EAST-WEST ORIENTED
SUBTROPICAL RIDGE (STR) EXTENDING ALONG 22N EASTWARD TO TAIWAN WITH
ZONAL WESTERLY FLOW NORTH OF THE STR.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TS 24W IS FORECAST TO CONTINUE TRACKING WEST-NORTHWESTWARD
THROUGH THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE DEEP
STR POSITIONED TO THE NORTH. THERE IS HIGH CONFIDENCE IN THE JTWC
FORECAST TRACK BASED ON THE SOLID STEERING RIDGE AND TIGHT AGREEMENT
IN DYNAMIC MODEL GUIDANCE THROUGH TAU 48 WITH A 65NM SPREAD. AFTER
TAU 48, THE DYNAMIC MODELS DIVERGE SLIGHTLY WITH INCREASED
UNCERTAINTY IN WHERE THE REMNANTS OF THE SYSTEM WILL TRACK. THE
MAJORITY OF MODELS SLOWLY TRACK THE REMNANTS INTO NORTHERN VIETNAM
THEN BACK OVER THE GULF OF TONKIN. AFTER A BRIEF STEADY PERIOD, TS
24W IS FORECAST TO INTENSIFY AFTER TAU 06 DUE TO THE GENERALLY
FAVORABLE ENVIRONMENT AND DIURNAL TRENDS. ALTHOUGH TS 24W IS
EXPECTED TO TRACK OVER MARGINAL OCEAN HEAT CONTENT, STRONG RADIAL
OUTFLOW SHOULD OFFSET ANY MITIGATING FACTORS. TS 24W IS FORECAST TO
PEAK NEAR 85 KNOTS BY TAU 24 BUT SHOULD GRADUALLY WEAKEN AS IT
TRACKS ALONG THE COAST OF VIETNAM AFTER TAU 24. THE SYSTEM SHOULD
WEAKEN FURTHER AS IT MAKES LANDFALL AND IS FORECAST TO RAPIDLY
WEAKEN OVER NORTHERN VIETNAM DUE TO FRICTIONAL EFFECTS.//
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