wxman57 wrote:New ASCAT just in. Max winds 25 kts and an elongated LLC that's well-removed from the MLC about 120 miles to the NW (near 10.2N/128E and off the chart below). Clearly, the trend is toward weakening not strengthening.
close to JT...
WDPN31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 05W (PEIPAH)
WARNING NR 23//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION (TD) 05W (PEIPAH), LOCATED APPROXIMATELY 631
NM EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTH-
NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED
INFRARED IMAGERY (EIR) DEPICTS SLOW CONSOLIDATION OF DEEP CONVECTION
CLUSTERS WITH FORMATIVE BANDING AROUND A LOW LEVEL CIRCULATION
CENTER (LLCC). A MOSAIC OF RECENT MICROWAVE IMAGERY SUGGESTS THERE
MAY BE SEVERAL WEAK VORTICES ROTATING AROUND THE LLCC, WHICH MAY BE
HAMPERING THE LOW LEVEL DEVELOPMENT. THE INITIAL POSITION IS BASED
ON A CENTROID OF POSSIBLE CENTERS BASED ON THE AFOREMENTIONED EIR
AND MICROWAVE IMAGERY WITH POOR CONFIDENCE. UPPER LEVEL ANALYSIS
REVEALS MODERATE (15-20 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS),
WITH SOME SLIGHT UPPER LEVEL TROUGHING IMPINGING ON THE SOUTHWEST
CORNER OF THE SYSTEM, HOWEVER THESE NEGATIVE EFFECTS ARE OFFSET BY
STRONG DIFFLUENCE AND GOOD POLEWARD OUTFLOW. THE INITIAL INTENSITY
IS ASSESSED AT 30 KNOTS BASED ON DVORAK CURENT INTENSITY ESTIMATES
FROM ALL AGENCIES. TD 05W HAS TRACKED ERRATICALLY OVER THE PAST 12
HOURS, PARTIALLY AS A RESULT OF THE POOR CERTAINTY OF THE BEST
TRACK. TD 05W IS IN A WEAK STEERING ENVIRONMENT, AS THE WESTERN
EXTENT OF THE SUB-TROPICAL RIDGE (STR) IS BEING ERODED.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TD 05W IS FORECAST TO REMAIN IN THE WEAK STEERING ENVIRONMENT
THROUGH TAU 48 AND TRACK SLOWLY NORTHWESTWARD TOWARD THE WEAKNESS IN
THE SUBTROPICAL RIDGE (STR). DYNAMIC GUIDANCE VARIES GREATLY BOTH IN
DIRECTION AND SPEED OF MOTION. THIS UNCERTAINTY IS ALSO REFLECTED IN
NUMEROUS ENSEMBLE MODEL PRODUCTS. THE MULTI-MODEL CONSENSUS SHIFTED
SOUTHWARD DURING THIS CYCLE. THE JTWC FORECAST TRACK IS SHIFTED
SLIGHTLY SOUTHWARD TO ACCOUNT FOR THIS, BUT REMAINS NORTH OF THE
CONSENSUS TAKING INTO ACCOUNT SOME UNLIKELY MODEL OUTLIERS. TD 05W
SHOULD GRADUALLY INCREASE TO AN INTENSITY OF 40 KNOTS BY TAU 48 AS
THE FOREWARD MOTION BEGINS TO INCREASE AND THE SYSTEM TRACKS INTO
LOWER VWS, BUT THIS INTENSIFICATION MAY NOT OCCUR IF THE LOW LEVEL
STRUCTURE DOES NOT BECOME MORE ORGANIZED.
C. IN THE EXTENDED TAUS, TD 05W IS EXPECTED TO TURN WEST-
NORTHWESTWARD AND ACCELERATE AS THE STR RE-BUILDS NORTH OF THE
SYSTEM. THE JTWC FORECAST TRACK SPEEDS HAVE BEEN ADJUSTED DOWNWARD
RELATIVE TO PRIOR FORECASTS TO TAKE INTO ACCOUNT THE SLOWER MOTION
OBSERVED IN THE NUMERICAL GUIDANCE. TD 05W SHOULD WEAKEN AS IT
TRACKS OVER THE PHILIPPINES, WITH MODELS INCREASINGLY FAVORING
DISSIPATION OVER THE CENTRAL PHILIPPINES BY TAU 120. DUE TO THE
UNCERTAINTY IN THE INITIAL POSITION AS WELL AS MAJOR TRACK AND TRACK
SPEED DIFFERENCES AMONG THE DYNAMIC MODELS, THERE IS LOW CONFIDENCE
IN THE JTWC TRACK FORECAST.//
NNNN