Tropical Storm KROVANH Advisory 16 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY)
WARNING NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 20W (TWENTY), LOCATED APPROXIMATELY 370 NM
EAST-NORTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. TD 20W HAS CONSOLIDATED INTO A DEPRESSION
DURING THE PAST SIX HOURS AS A FLARE OF DEEP CONVECTION DEVELOPED
OVER THE NORTHWESTERN PORTION OF THE LLCC. THE CURRENT POSITION IS
BASED ON A 141620Z SSMI PASS, WHICH SHOWS A PARTIALLY-EXPOSED LOW-
LEVEL CIRCULATION CENTER (LLCC). THE INTENSITY OF 25 KNOTS IS
CONSISTENT WITH DVORAK T-NUMBER ESTIMATES FROM PGTW AND KNES. THE
SYSTEM IS TRACKING NORTHWESTWARD ALONG THE PERIPHERY OF A
SUBTROPICAL STEERING RIDGE TO THE NORTHEAST. TD 20W LIES SLIGHTLY
EQUATORWARD OF AN UPPER-LEVEL RIDGE AXIS IN AN AREA OF MODERATE
EASTERLY VERTICAL WIND SHEAR.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST
PHILOSOPHY.
   B. TD 20W IS EXPECTED TO TRACK GENERALLY NORTHWESTWARD OVER THE
NEXT 72 HOURS AS SUBTROPICAL RIDGING BECOMES FIRMLY ESTABLISHED TO
THE NORTH. THE SYSTEM SHOULD INTENSIFY SLOWLY IN THE NEAR-TERM WHILE
VERTICAL WIND SHEAR REMAINS UNFAVORABLE. AFTER TAU 48, THE SYSTEM
WILL LIKELY INTENSIFY MORE RAPIDLY AS VERTICAL WIND SHEAR DECREASES
AND UPPER-LEVEL OUTFLOW INCREASES. DYNAMIC MODEL GUIDANCE IS IN
GENERALLY GOOD AGREEMENT REGARDING THE FORECAST TRACK THROUGH TAU
72. THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE OFFICIAL
FORECAST, WHICH LIES CLOSE TO THE MULTI-MODEL CONSENSUS.
   C. IN THE EXTENDED PERIOD, TD 20W WILL TURN POLEWARD AROUND THE
STEERING RIDGE AXIS. STEADY TO RAPID INTENSIFICATION IS EXPECTED AS
THE SYSTEM MAKES THE TURN, BUT INCREASING VERTICAL WIND SHEAR AND
PASSAGE OVER COOLER WATER SHOULD PRODUCE GRADUAL WEAKENING AND
INITIATE THE EARLY STAGE OF EXTRATROPICAL TRANSITION BY TAU 120.
DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT REGARDING TIMING OF THE
TURN AROUND OR JUST AFTER TAU 72, BUT ARE IN LESS AGREEMENT
REGARDING THE ORIENTATION OF THE TRACK FOLLOWING THE TURN. ONE
GROUPING OF MODELS, INCLUDING GFS AND HWRF, PREDICTS A TIGHTER TURN
INSIDE THE MULTI-MODEL CONSENSUS AND ANOTHER GROUPING, INCLUDING THE
UKMET AND ECMWF MODELS, PREDICTS A WIDER TURN TO THE WEST OF THE
MULTI-MODEL CONSENSUS. THE CURRENT FORECAST LIES CLOSE TO THE
CONSENSUS BUT SLIGHTLY FAVORS THE WESTERN GROUPING GIVEN A WESTWARD
SHIFT IN MODEL FORECASTS OVER THE PAST SEVERAL MODEL RUNS. GIVEN
MODEL FORECAST SPREAD, CONFIDENCE IN THE EXTENDED TRACK FORECAST IS
LOW.//
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