Tropical Storm HAISHEN Advisory Sat Apr 04

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 05W (FIVE) WARNING
NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 05W (FIVE), LOCATED APPROXIMATELY 227 NM
EAST OF CHUUK, HAS TRACKED WEST-NORTHWESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A PARTIALLY-EXPOSED, ELONGATED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH DEEP CONVECTIVE BANDING WRAPPING FROM THE NORTH QUADRANT
INTO THE WEST QUADRANT OF THE LLCC. A 030527Z SSMIS PARTIAL 91 GHZ
IMAGE REVEALS DEFINED SHALLOW BANDING WRAPPING BROADLY OVER THE
EASTERN SEMI-CIRCLE INTO A WEAKLY-DEFINED LLCC. BASED ON THE WEAK
NATURE OF THE LLCC AND LACK OF HIGH-RESOLUTION MICROWAVE IMAGERY,
THERE IS FAIR CONFIDENCE IN THE INITIAL POSITION. THE INITIAL
INTENSITY IS ASSESSED AT 30 KNOTS, SLIGHTLY HIGHER THAN THE DVORAK
ESTIMATES OF 25 KNOTS, BASED ON A RECENT ASCAT IMAGE SHOWING 25 TO
30 KNOT WINDS OVER THE WESTERN SEMI-CIRCLE. UPPER-LEVEL ANALYSIS
INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT WITH 5 TO 10 KNOT
VERTICAL WIND SHEAR (VWS) OFFSET BY GOOD POLEWARD OUTFLOW. TD 05W IS
TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF A WEAK EXTENSION
OF THE SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 05W WILL CONTINUE TRACKING WESTWARD THROUGH TAU 24 TO 36
UNDER THE INFLUENCE OF THE STR. HOWEVER, THE STR IS EXPECTED TO
WEAKEN AND RETREAT AS A DEEP MIDLATITUDE SHORTWAVE TROUGH DEEPENS TO
THE WEST. THIS WILL SERVE TO WEAKEN THE STEERING ENVIRONMENT AND
PRODUCE A PERIOD OF QUASI-STATIONARY MOTION. HENCE, DYNAMIC GUIDANCE
IS IN POOR AGREEMENT WHILE GENERALLY INDICATING A QUASI-STATIONARY,
LOOPING MOTION. TD 05W IS FORECAST TO INTENSIFY TO A PEAK INTENSITY
OF 45 KNOTS PRIMARILY DUE TO IMPROVED POLEWARD OUTFLOW ASSOCIATED
WITH THE AFOREMENTIONED TROUGH. AFTER TAU 48, TD 05W SHOULD BEGIN TO
SLOWLY TRACK NORTHEASTWARD AS THE NEAR-EQUATORIAL RIDGE BUILDS TO
THE SOUTHEAST AND BECOMES THE PRIMARY STEERING INFLUENCE.
   C. BEYOND TAU 72, TD 05W IS FORECAST TO WEAKEN DUE TO HIGHER
VERTICAL WIND SHEAR ASSOCIATED WITH THE TROUGH, LEADING
TO ITS DISSIPATION NEAR TAU 96. AVAILABLE MODEL GUIDANCE IS IN
GENERAL AGREEMENT ON THE FORECAST SCENARIO; HOWEVER, THERE IS A HIGH
DEGREE OF UNCERTAINTY IN THE FORWARD SPEED AND TIMING OF THE
NORTHEASTWARD SHIFT IN TRACK. DUE TO THESE FACTORS THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST.//
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