Tropical Storm CHOI-WAN Advisory Qua, 02-06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN)
WARNING NR 014//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 04W (CHOI-WAN), LOCATED APPROXIMATELY
137 NM SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-
NORTHWESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALY EXPOSED LOW-
LEVEL CIRCULATION (LLC) WITH DEEP CONVECTION BEING SHEARED TO THE
SOUTHWEST OF THE CENTER. THE INITIAL POSITION IS PLACED WITH
MODERATE CONFIDENCE BASED ON RADAR IMAGERY AND A 012215Z 91GHZ SSMIS
IMAGE WHICH DEPICT EXPOSED LOW LEVEL BANDING WITH DEEP FLARING
CONVECTION ON THE WESTERN PERIPHERY OF THE SYSTEM. THE INITIAL
INTENSITY REMAINS AT 30 KNOTS BASED ON A SEA LEVEL PRESSURE
OBSERVATION OF 999.6MB FROM ROMBLON (RPMR), WHICH CORRESPONDS TO 31
KNOTS ON THE WIND-PRESSURE RELATIONSHIP TABLE. TD 04W IS CURRENTLY
IN A MARGINALLY FAVORABLE ENVIRONMENT WITH LOW (<15 KTS) VERTICAL
WIND SHEAR (VWS), ROBUST EQUATORWARD OUTFLOW AND WARM (30C) SSTS
OFFSET BY CONVERGENT FLOW ALOFT DUE TO AN UPPER LEVEL TROUGH. TD 04W
IS TRACKING ALONG THE SOUTHWEST EDGE OF A SUBTROPICAL RIDGE (STR) TO
THE NORTH AND NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY.
   B. TD 04W IS FORECAST TO BEGIN TURNING NORTHWESTWARD AND REACH AN
INTENSITY OF 35KTS OVER THE SIBUYAN SEA JUST BEFORE MAKING LANDFALL
OVER LUZON AND PASSING SLIGHTLY TO THE WEST OF MANILA. THE
MOUNTAINOUS TERRAIN OF WESTERN LUZON WILL DISRUPT THE LOW LEVEL
CIRCULATION, WEAKENING THE SYSTEM TO 30 KTS BY TAU 24. WHEN IT
REEMERGES OVER WATER, THE SYSTEM WILL BE IN A LESS FAVORABLE
ENVIRONMENT WITH MODERATE (15-25 KTS) VWS CAUSED BY UPPER-LEVEL
EASTERLIES. THIS WEAKENING TREND WILL CONTINUE AS TD 04W BEGINS TO
RECURVE NORTH-NORTHEASTWARD AROUND THE AXIS OF THE STR NEAR TAU 48.
AFTER TAU 48, TD 04W TRACKS INTO THE WESTERLIES WHICH FURTHER
WEAKENS THE SYSTEM WITH DISSIPATION BY TAU 72. THE JTWC FORECAST
TRACK LIES SLIGHTLY WEST OF THE MULTI-MODEL CONSENSUS THROUGHOUT THE
FORECAST PERIOD, BUT DUE TO THE UNCERTAINTY OF THE IMPACT OF THE
LAND INTERACTION, THERE IS LOW CONFIDENCE IN BOTH THE JTWC FORECAST
TRACK AND INTENSITY.//
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