Tropical Storm KOPPU Advisory Qua, 14-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOPPU) WARNING
NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 24W (KOPPU), LOCATED APPROXIMATELY 877 NM EAST
OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS BECOME PARTIALLY EXPOSED
FROM A DEEPENING CENTRAL DENSE OVERCAST FEATURE. THE INITIAL POSITION
LINES UP WELL WITH THE LLCC FEATURE IN THE 132212Z SSMI-S MICROWAVE
PASS. THE INITIAL INTENSITY OF 45 KNOTS IS HELD SLIGHTLY HIGHER THAN
AGENCY DVORAK ESTIMATES TO REFLECT THE DEEPENED STATE OF THE CYCLONE.
UPPER LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT
WITH AN ANTICYCLONE JUST NORTH OF THE SYSTEM, PROVIDING STRONG
DIVERGENT OUTFLOW. HOWEVER, MODERATE (15-20 KNOT) NORTHEASTERLY
VERTICAL WIND SHEAR (VWS) IS PREVENTING FASTER INTENSIFICATION. SEA
SURFACE TEMPERATURES (SSTS) ARE NEAR 30 CELSIUS. TS 24W IS TRACKING
ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE
(STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 24W WILL CONTINUE TO TRACK WESTWARD THROUGH THE REMAINDER
OF THE FORECAST PERIOD UNDER THE STEERING INFLUENCE OF THE STR.
EXPECT SLOW INTENSIFICATION OVER THE NEXT 48 HOURS AS VWS CONTINUES
TO HINDER DEVELOPMENT. BEYOND TAU 48, VWS WILL RELAX AS THE UPPER
LEVEL WIND FLOW BECOMES MORE IN-PHASE WITH THE STORM MOTION.
ADDITIONALLY, SSTS WILL INCREASE ABOVE 30 CELSIUS. THESE WILL SUPPORT
AN INCREASED RATE OF INTENSIFICATION AS THE SYSTEM APPROACHES LUZON.
   C. IN THE EXTENDED FORECAST, TS KOPPU WILL CONTINUE ON A WESTWARD
TRACK AS THE STR REMAINS THE DOMINANT STEERING MECHANISM. THE STORM
WILL SLOW AS IT REACHES THE WESTERN EXTENT OF THE STR AND UNDERGO A
RAPID INTENSIFICATION (RI) DUE TO THE FAVORABLE ENVIRONMENTAL
CONDITIONS, IN ADDITION TO INCREASED POLEWARD OUTFLOW AT THE EDGE OF
THE STR. THE RI WILL PEAK THE SYSTEM TO 120 KNOTS - POSSIBLY STRONGER
- RIGHT BEFORE LANDFALL INTO LUZON AT TAU 90. DYNAMIC MODEL GUIDANCE
IS IN GOOD AGREEMENT ON THE OVERALL TRACK; HOWEVER, A BIFURCATION
REMAINS AT THE END OF THE FORECAST PERIOD WHEN THE CYCLONE NEARS
LUZON. DUE TO THIS, THERE IS HIGH CONFIDENCE IN THE JTWC TRACK
FORECAST ONLY UP TO TAU 72.//
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