Tropical Storm KAMMURI Advisory Thu Sep 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (KAMMURI)
WARNING NR 03//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 17W (KAMMURI), LOCATED APPROXIMATELY 498 NM
SOUTHEAST OF IWO TO, HAS TRACKED WESTWARD AT 02 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 242203Z SSMIS
PASS AND A PARTIAL 250005Z ASCAT PASS. THE BEST TRACK POSITION HAS
BEEN RELOCATED APPROXIMATELY 90 NM TO THE SOUTHWEST OF THE PREVIOUS
ESTIMATE BASED ON THE CLARIFYING MICROWAVE IMAGERY AND ASCAT DATA.
THE CURRENT INTENSITY OF 30 KNOTS IS CONSISTENT WITH DVORAK T-NUMBER
ESTIMATES FROM PGTW AND KNES AND PERIPHERAL WINDS EVIDENT IN THE
AFOREMENTIONED ASCAT PASS. TD 17W IS TRACKING VERY SLOWLY WESTWARD
ALONG THE SOUTHERN PERIPHERY OF A DEVELOPING SUBTROPICAL STEERING
RIDGE TO THE NORTH. THE BROAD LOW-LEVEL CIRCULATION CENTER (LLCC) IS
DEVOID OF CENTRAL DEEP CONVECTION DUE TO SUBSIDENCE ALOFT INDUCED BY
A NEARBY UPPER-LEVEL TROUGH. STRONG UPPER-LEVEL DIFFLUENCE AND
CONVERGENT LOW-LEVEL FLOW ARE FUELING SUSTAINED DEEP CONVECTION WELL
TO THE NORTHEAST OF THE CIRCULATION CENTER.
3. FORECAST REASONING.
   A. FORECAST TRACK SPEEDS IN THE TAU 72 TO TAU 96 PERIOD HAVE
DECREASED FROM THE PREVIOUS WARNING DUE TO A SLOWER ANTICIPATED
RECURVATURE INTO THE MID-LATITUDE WESTERLIES. AS A RESULT,
EXTRATROPICAL TRANSITION IS NOT EXPECTED TO BEGIN UNTIL AFTER TAU
72. OTHERWISE, THERE ARE NO SIGNIFICANT CHANGES IN THE FORECAST
PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 17W IS EXPECTED TO MOVE NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF THE DEVELOPING STEERING RIDGE THROUGH TAU
72. THERE IS SOME UNCERTAINTY IN THE TRACK AMONG CONSENSUS MODELS. A
WESTWARD GROUPING CONSISTING OF THE JAPANESE GLOBAL MODEL AND
ENSEMBLE, NAVGEM, GFDN, AND ECMWF DEPICTS A MORE CONTINUOUS STEERING
RIDGE AND, CONSEQUENTLY, A TRACK FARTHER TO THE WEST FOLLOWED BY A
SLOWER AND SHARPER RECURVATURE. THE POLEWARD GROUPING CONSISTING OF
HWRF, UKMET, GFS, AND THE GFS ENSEMBLE SHOW THE RIDGE BREAKING DOWN
EARLY AND THE SYSTEM TRACKING NORTH-NORTHWESTWARD THROUGH TAU 72
FOLLOWED BY A BROADER RECURVATURE. THE CURRENT FORECAST FAVORS THE
WESTWARD GROUPING THROUGH TAU 72 BASED ON ANALYSIS OF THE DEVELOPING
STEERING RIDGE AND ITS ORIENTATION. THE SYSTEM WILL INTENSIFY SLOWLY
OVER THE NEXT 24 TO 36 HOURS AS TROUGHING ALOFT SUPPRESSES CENTRAL
CONVECTION. THEREAFTER, AS THE UPPER-LEVEL TROUGH FILLS AND UPPER-
LEVEL OUTFLOW IS ENHANCED AROUND THE RIDGE PERIPHERY, STEADIER
INTENSIFICATION IS ANTICIPATED. MARGINAL OCEAN HEAT CONTENT IS
EXPECTED TO LIMIT THE PEAK INTENSITY TO AROUND 75 KNOTS AT TAU 72.
   C. IN THE EXTENDED PERIOD, TD 17W IS EXPECTED TO ROUND THE
SUBTROPICAL RIDGE AXIS AND UNDERGO EXTRATROPICAL TRANSITION AS IT
ACCELERATES INTO THE MID-LATITUDE WESTERLIES. THERE IS SOME
UNCERTAINTY REGARDING WHERE AND HOW QUICKLY THE SYSTEM WILL RECURVE
DUE TO SPREAD IN THE MODEL GUIDANCE DISCUSSED EARLIER. THE CURRENT
FORECAST IS GENERALLY CONSISTENT WITH THE SLOW AND SHARPER
RECURVATURE DEPICTED IN THE WESTWARD MODEL GROUPING, AND LIES WEST
OF THE MULTI-MODEL CONSENSUS. GIVEN THE MODEL UNCERTAINTY, THERE IS
LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
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