Tropical Storm NURI Advisory Sat Nov 01

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 (TD) 20W (TWENTY), LOCATED APPROXIMATELY 211
NM NORTH-NORTHWEST OF YAP, HAS TRACKED WESTWARD AT 08 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
REVEALS A PERSISTENT CONSOLIDATION OF THE SYSTEM AS A SMALL CENTRAL
DENSE OVERCAST (CDO) FEATURE HAS PERSISTED OVER THE LOW LEVEL
CIRCULATION CENTER (LLCC) WHILE CONVECTIVE BANDING REMAINS DEFINED.
A 310540Z SSMI MICROWAVE IMAGE SHOWS SOME TIGHTLY CURVED CONVECTIVE
BANDING ALONG THE LLCC WHILE THE OVERALL STRUCTURE OF THE SYSTEM HAS
IMPROVED. THE INITIAL POSITION IS BASED UPON THE CDO FEATURE IN THE
MSI LOOP AND THE MICROWAVE IMAGE WITH GOOD CONFIDENCE. THE INITIAL
INTENSITY OF 30 KNOTS IS BASED ON DVORAK INTENSITY ESTIMATES OF THE
SAME VALUE FROM ALL REPORTING AGENCIES AND FROM A PREVIOUS 310010Z
ASCAT PASS. UPPER LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT
AS THE SYSTEM IS LOCATED SOUTH OF THE RIDGE AXIS IN AN AREA WITH LOW
(05-10 KNOT) VERTICAL WIND SHEAR (VWS) AND GOOD OUTFLOW. TD 20W IS
CURRENTLY TRACKING WEST ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION
OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE NORTHEAST OF THE
SYSTEM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TD 20W IS EXPECTED TO TRACK MORE WEST-NORTHWEST IN THE NEXT 2
DAYS AS THE SYSTEM TRACKS AROUND THE SOUTHWESTERN PERIPHERY OF THE
STR. AFTER TAU 48, THE SYSTEM IS EXPECTED TO TURN MORE POLEWARD AS A
MID-LATITUDE TROUGH DIGS ACROSS JAPAN AND MODIFIES THE STR.
FAVORABLE UPPER LEVEL CONDITIONS, IN ADDITION TO VERY WARM SEA
SURFACE TEMPERATURES IN THE PHILIPPINE SEA (GREATER THAN 28
CELSIUS), WILL INDUCE STRONG INTENSIFICATION, PEAKING AT 105 KNOTS
BY TAU 72. NUMERIC MODEL GUIDANCE, ALONG WITH ENSEMBLE DATA, IS IN
GOOD AGREEMENT WITH THIS PORTION OF THE FORECAST, LENDING TO HIGH
CONFIDENCE THROUGH TAU 72.
   C. AFTER TAU 72, TD 20W IS EXPECTED TO SLOWLY DRIFT POLEWARD INTO
A WEAK STEERING ENVIRONMENT AS THE CURRENT STEERING STR RECEDES TO
THE EAST AND ANOTHER STR BUILDS IN FROM THE WEST, LEAVING THE SYSTEM
IN A COL AREA WITH A POSSIBILITY OF QUASI-STATIONARY MOTION.
INCREASING VWS AFTER TAU 72 IS EXPECTED TO INDUCE A SLIGHT WEAKENING
TREND THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL GUIDANCE
IS WIDELY SPREAD IN THIS PORTION OF THE FORECAST TRACK DUE TO THE
EXPECTED WEAK STEERING ENVIRONMENT AND DIFFERENT SOLUTIONS IN THE
EXTENT OF THE STR. DUE TO THIS, THERE IS LOW CONFIDENCE IN THE
EXTENDED PORTION OF THE FORECAST.//
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