Tropical Storm KROVANH Advisory Tue Sep 15

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY)
WARNING NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 20W (TWENTY), LOCATED APPROXIMATELY 366 NM
EAST-NORTHEAST OF SAIPAN, HAS TRACKED NORTHWESTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 142126Z
SSMIS IMAGE AND A 142322Z ASCAT PASS. THE INTENSITY OF 30 KNOTS IS
CONSISTENT WITH THE ASCAT DATA AND DVORAK T-NUMBER ESTIMATES FROM
MULTIPLE REPORTING AGENCIES. TD 20W CONTINUES TO TRACK NORTHWESTWARD
ALONG THE PERIPHERY OF A SUBTROPICAL STEERING RIDGE TO THE NORTHEAST.
THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS REMAINED PARTIALLY
EXPOSED DUE TO PERSISTENT EASTERLY VERTICAL WIND SHEAR. DEEP
CONVECTION IS CONFINED TO THE NORTHWESTERN PERIPHERY OF THE LLCC.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY FROM THE
PREVIOUS WARNING.
   B. TD 20W WILL CONTINUE TRACKING GENERALLY NORTHWESTWARD OVER THE
NEXT 72 HOURS AS SUBTROPICAL RIDGING BECOMES FIRMLY ESTABLISHED TO
THE NORTH. SLOW INTENSIFICATION IS EXPECTED IN THE NEAR-TERM AS
PERSISTENT EASTERLY VERTICAL WIND SHEAR OFFSETS THE FAVORABLE
INFLUENCES OF WARM SEA SURFACE TEMPERATURES AND IMPROVING WESTWARD
OUTFLOW ALOFT. AFTER TAU 36, THE SYSTEM WILL LIKELY INTENSIFY MORE
RAPIDLY AS VERTICAL WIND SHEAR DECREASES AND UPPER-LEVEL OUTFLOW
INCREASES. DYNAMIC MODEL GUIDANCE REMAINS 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 ROUND THE STEERING RIDGE
AXIS AND ACCELERATE TOWARD THE MIDLATITUDE BAROCLINIC ZONE BY TAU
120. STEADY INTENSIFICATION IS EXPECTED AS THE SYSTEM MAKES THE
TURN, BUT INCREASING VERTICAL WIND SHEAR AND PASSAGE OVER COOLER
WATER WILL LIKELY WEAKEN THE SYSTEM AND INITIATE THE FIRST STAGE OF
EXTRATROPICAL TRANSITION BY TAU 120. DYNAMIC MODEL GUIDANCE IS IN
GOOD AGREEMENT REGARDING TIMING OF THE AROUND TAU 72, BUT AGAIN SHOW
LESS AGREEMENT REGARDING THE ORIENTATION OF THE TRACK FOLLOWING THE
TURN. THE MODEL SOLUTIONS DURING THE EXTENDED PERIOD ARE FAIRLY
EVENLY DISTRIBUTED AROUND THE CONSENSUS WITH NO MODEL GROUPINGS
READILY APPARENT IN THE CURRENT RUN. THE OFFICIAL FORECAST LIES
SLIGHTLY WEST OF THE CONSENSUS IN THE EXTENDED PERIOD, CONSISTENT
WITH THE PREVIOUS FORECAST. GIVEN MODEL FORECAST SPREAD, CONFIDENCE
IN THE EXTENDED TRACK FORECAST IS LOW.//
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