#26 Postby euro6208 » Wed Aug 02, 2017 12:09 am
WDPN33 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (NALGAE)
WARNING NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TROPICAL DEPRESSION 13W (NALGAE), LOCATED APPROXIMATELY 392 NM
NORTH OF WAKE ISLAND, HAS TRACKED NORTHEASTWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS
FLARING CONVECTION CONSOLIDATING OVER A PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE PGTW SATELLITE FIX POSITION. A 012303Z AMSU
89 GHZ MICROWAVE IMAGE CONFIRMS THE POSITION FIX AND DEPICTS DEEP
CONVECTIVE BANDING INTO THE LLCC FROM THE SOUTHERN AND EASTERN
QUADRANTS. THE INITIAL INTENSITY IS ASSESSED AT 30 KNOTS AND IS ON
THE UPPER END OF MULTI AGENCY DVORAK ESTIMATES OF T1.5 TO T2.0 (25
TO 30 KNOTS) BASED ON A 012303Z SCATTEROMETER PASS SHOWING A BROAD
AREA OF 30 KNOT WINDS ALONG THE SOUTHEASTERN PERIPHERY, WITH SOME 30
KNOT WINDS INDICATED WRAPPING IN ALONG THE NORTHERN EDGE AS WELL. TD
13W LIES IN AREA OF LOW TO MODERATE (15-20 KNOTS) VERTICAL WIND
SHEAR (VWS) AND WARM SEA SURFACE TEMPERATURES (SST) (27-28 DEG
CELSIUS). THE SYSTEM IS TAPPING INTO A ROBUST EASTERLY OUTFLOW
CHANNEL INTO A TUTT CELL NEAR THE DATELINE. TD 13W IS TRACKING
NORTHEASTWARD ALONG THE NORTHWESTERN BOUNDARY OF A NEAR EQUATORIAL
RIDGE (NER) LOCATED TO THE SOUTHEAST.
3. FORECAST REASONING.
A. NO CHANGE TO THE FORECAST TRACK PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
B. TD 13W WILL SLOW SIGNIFICANTLY, BECOMING NEARLY QUASI-
STATIONARY OVER THE NEXT 12 HOURS, AS A STRONG NORTH-SOUTH ORIENTED
BLOCKING RIDGE DEVELOPS ALONG THE DATELINE, BLOCKING FURTHER
EASTWARD MOVEMENT. THIS BLOCKING RIDGE BECOMES THE PRIMARY STEERING
MECHANISM AFTER TAU 24, PUSHING TD 13W ONTO A NORTH THEN
NORTHWESTWARD TRACK FROM TAU 24 THROUGH TAU 72. TD 13W WILL CONTINUE
TO STEADILY INTENSIFY THROUGH TAU 48 AS VWS CONTINUES TO DECREASE,
EASTWARD OUTFLOW REMAINS IN PLACE AND THE SYSTEM TRACKS OVER WARM
WATERS 26-28 DEG C). AFTER PEAKING AT TAU 48 THE SYSTEM WILL START A
SLOW WEAKENING TREND AS IT BEGINS TO TRACK OVER PROGRESSIVELY COOLER
WATERS, AND THE EASTWARD OUTFLOW CHANNEL DISSIPATES. THE SYSTEM IS
FORECAST TO BEGIN EXTRATROPICAL TRANSITION BY TAU 72, AS IT
INTERACTS WITH A DEEP UPPER-LEVEL TROUGH DIGGING SOUTHWARDS AND
STARTS TO LOSE ITS TROPICAL CHARACTERISTICS. DYNAMIC MODEL GUIDANCE
IS IN STRONG AGREEMENT THAT THE SYSTEM WILL TURN TO THE NORTH BUT
THERE REMAIN RELATIVELY MINOR VARIANCES IN THE EXACT TIMING AND
SHARPNESS OF THE TURN. OVERALL THERE IS HIGH CONFIDENCE IN THIS
PORTION OF THE FORECAST TRACK.
C. AFTER TAU 72, TD 13W IS FORECAST TO CONTINUE TRACKING NORTH-
NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF A STRONG STR LOCATED TO
THE EAST. THE SYSTEM WILL BEGIN TO WEAKEN AFTER TAU 72 AS IT STARTS
TO TRACK UNDERNEATH AN UPPER-LEVEL LOW, LOSE ITS SOURCE OF OUTFLOW
AND COMPLETE EXTRA-TROPICAL TRANSITION BY TAU 96 AS IT BECOMES
ABSORBED INTO A BROAD AND DEEP UPPER-LEVEL LOW SYSTEM. MODEL
GUIDANCE IS IN AGREEMENT THAT THE TRACK WILL CONTINUE TO THE NORTH-
NORTHWESTWARD, WITH A LARGE SPREAD IN THE EXACT TRACK BASED ON THE
STRENGTH AND ORIENTATION OF THE BLOCKING RIDGE TO THE EAST. DUE TO
THE INCREASED MODEL SPREAD, THERE IS OVERALL LOW CONFIDENCE IN THIS
PORTION OF THE JTWC TRACK FORECAST.//
NNNN
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