Tropical Storm BOLAVEN Advisory mar, 02-01

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING
NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01W (ONE), LOCATED APPROXIMATELY 377 NM
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 16 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH A SYMMETRIC AREA OF DEEP
CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) AND
IMPROVED CONVECTIVE BANDING OVER THE NORTHERN SEMI-CIRCLE. A 011829Z
SSMI 85GHZ IMAGE SHOWS CURVED DEEP CONVECTIVE BANDING WRAPPING INTO
THE NORTHWEST AND WEST QUADRANTS OF THE SYSTEM WITH A PARTIALLY-
EXPOSED LLCC POSITIONED ON THE SOUTHEAST EDGE OF THE CENTRAL
CONVECTION. THEREFORE, THERE IS FAIR CONFIDENCE IN THE INITIAL
POSITION. A 011331Z ASCAT PARTIAL IMAGE REVEALED 25-30 KNOT
NORTHERLY WINDS OVER THE BOHOL SEA, JUST NORTH OF MINDANAO, WHICH
SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 30 KNOTS. UPPER-LEVEL
ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH LOW TO
MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS) OFFSET BY STRONG
EASTERLY DIFFLUENT FLOW ALOFT. TD 01W IS TRACKING QUICKLY WESTWARD
ACROSS THE PHILIPPINES UNDER THE STEERING INFLUENCE OF AN EAST-WEST
ORIENTED LOW-LEVEL SUBTROPICAL RIDGE POSITIONED TO THE NORTH.
3. FORECAST REASONING.
   A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE
FORECAST PHILOSOPHY.
   B. TD 01W IS FORECAST TO CONTINUE TRACKING QUICKLY WESTWARD
THROUGH TAU 36 UNDER THE STEERING INFLUENCE OF THE DEEP-LAYERED LOW-
TO MID-LEVEL SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN GENERALLY FAVORABLE
THROUGH TAU 36, HOWEVER, INTERACTION WITH LAND SHOULD SLOW
DEVELOPMENT WITH A PEAK INTENSITY OF 45 KNOTS FORECAST AT TAU 24 AND
TAU 36 AS THE SYSTEM TRACKS OVER THE SOUTH CHINA SEA. AFTER TAU 36,
TD 01W SHOULD TURN WEST-NORTHWESTWARD AND SLOW AS IT TRACKS ALONG
THE WESTERN PERIPHERY OF THE STR. GRADUAL WEAKENING IS EXPECTED DUE
TO INCREASING VWS AND COOLER SST (25-26C).
   C. AFTER THE SYSTEM MAKES LANDFALL OVER VIETNAM NEAR TAU 72, TD
01W WILL WEAKEN RAPIDLY AND SHOULD DISSIPATE BY TAU 96. DYNAMIC
MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 36 THEN RAPIDLY
DIVERGES WITH GFS AND THE GFS ENSEMBLE DEPICTING AN UNLIKELY RE-
CURVE NORTHWARD DIRECTLY INTO THE STR. THE JTWC FORECAST TRACK
FAVORS THE ECMWF SOLUTION AND IS POSITIONED JUST WEST OF THE MULTI-
MODEL CONSENSUS AT TAU 72 AND TAU 96. OVERALL, THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST TRACK DUE TO UNCERTAINTY IN THE
INITIAL POSITION AND THE LARGE SPREAD IN MODEL SOLUTIONS AFTER TAU
36.//
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