Tropical Storm NURI Advisory Sáb, 01-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (NURI) WARNING NR
06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (NURI), LOCATED APPROXIMATELY 358 NM
NORTHWEST OF YAP, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
CONTINUES TO SHOW CONSOLIDATING FEEDER BANDS SPIRALING TIGHTER INTO
THE LOW LEVEL CIRCULATION CENTER THAT IS OBSCURED BY A COMPACT
CENTRAL DENSE OVERCAST FEATURE. THE INITIAL POSITION IS BASED ON
THE MSI LOOP AND A 010443Z AMSU-B MICROWAVE IMAGE. THE INITIAL
INTENSITY OF 55 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK
ESTIMATES FROM PGTW, RJTD, AND KNES. UPPER LEVEL ANALYSIS INDICATES
THE SYSTEM IS AN AREA WITH MODERATE (10-20 KNOT) VERTICAL WIND
SHEAR AND EXCELLENT DUAL OUTFLOW CHANNELS. TS 20W CONTINUES TO
TRACK ALONG THE SOUTHERN PERIPHERY OF A WESTERN ANNEX OF THE
SUBTROPICAL RIDGE (STR), THE MAIN BODY OF WHICH IS TO THE NORTHEAST
OF THE SYSTEM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 20W WILL TAKE A MORE NORTHWESTWARD TRACK OVER THE NEXT 24
HOURS AS THE STR WEAKENS AND TRACKS TO THE EAST AND A MID-LATITUDE
TROUGH FROM THE NORTHWEST APPROACHES. BEYOND TAU 24, TS NURI WILL
TRACK NORTHWARD AS THE RIDGE RECEDES AND THE TROPICAL GOES INTO A
WEAKER STEERING ENVIRONMENT PROVIDED BY A COL REGION. 20W WILL
FOLLOW THE COL REGION IN A NORTHEAST PATTERN AS THE STR BUILDS BACK
IN, NOW EAST OF THE SYSTEM. FAVORABLE UPPER LEVEL CONDITIONS WILL
ALLOW THE SYSTEM TO  PEAK AT 120 KNOTS BY TAU 72. THE 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. IN THE EXTENDED FORECAST, THERE IS A SLIGHT BIFURCATION IN
THE MODELS WITH RESPECT TO THE EXTENT AND ORIENTATION OF THE STR TO
THE EAST. GFS AND ECMWF ARE THE WESTERN OUTLIERS, WITH THE RIDGE
REBUILDING IN STRONGLY WITH A SLIGHT BROAD BLOCKING PATTERN. THIS
WILL FORCE TS NURI TO TEMPORARILY BACK TO A NORTH-NORTHWESTWARD
TRACK AS THE STR REBUILDS BEFORE ACCELERATING NORTHEASTWARD,
GETTING ABSORBED INTO THE MID-LATITUDE WESTERLIES. THE NAVGEM
SOLUTION HAS A DIFFERENT, MORE ZONAL, ORIENTATION OF THE STR,
HAVING THE SYSTEM SIMPLY TRACK TO THE NORTHEAST AS IT BEGINS TO BE
ABSORBED IN THE WESTERLIES. BY TAU 96, THE CYCLONE WILL BEGIN EXTRA-
TROPICAL TRANSITION. SINCE MODEL GUIDANCE IS WIDELY SPREAD ON THIS
PORTION OF THE FORECAST TRACK DUE TO VARYING SOLUTIONS WITH THE
REBUILDING STR, THERE IS LOW CONFIDENCE IN THE EXTENDED PORTION OF
THE FORECAST.//
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