Tropical Storm NYATOH Advisory mar, 30-11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 27W (TWENTYSEVEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 12.3N 141.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 187 NM WEST-SOUTHWEST OF NAVSTA GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM WITH IMPROVED CONVECTIVE BANDING WRAPPING INTO
A RAGGED LOW-LEVEL CIRCULATION CENTER. UNFORTUNATELY, THERE IS NO
USEFUL MICROWAVE IMAGERY OR SCATTEROMETRY IMAGERY AVAILABLE,
THEREFORE, THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE.
THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE
AND IS HEDGED ABOVE THE PGTW AND KNES DVORAK ESTIMATES. WITH THE
EXCEPTION OF THE EASTERN QUADRANT, OUTFLOW IS VIGOROUS WITH
POLEWARD OUTFLOW ENHANCED BY STRONG WESTERLY FLOW TO THE NORTH.
ADDITIONALLY, VERTICAL WIND SHEAR IS LOW.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE(STR)
POSITIONED TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: HIGH, VERY FAVORABLE OCEAN HEAT CONTENT VALUES.
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 27W IS FORECAST TO TRACK WEST-NORTHWESTWARD
THROUGH TAU 36 UNDER THE STEERING INFLUENCE OF THE STR POSITIONED
TO THE NORTH. AFTER TAU 36, A DEEP MIDLATITUDE TROUGH IS FORECAST
TO DIG INTO THE EAST CHINA SEA, WHICH WILL WEAKEN THE STR AND
REALIGN THE STR TO A MORE POLEWARD CONFIGURATION. AS THE SYSTEM
TURNS MORE POLEWARD BETWEEN TAU 36 TO 48 IT IS EXPECTED TO SLOW AS
IT ENCOUNTERS A STRONG NORTHEAST SURGE EVENT. THEN GRADUALLY
ACCELERATE NORTH-NORTHEASTWARD AS THE SURGE EVENT WEAKENS BY TAU
72. RAPID INTENSIFICATION IS ANTICIPATED AFTER TAU 48 DUE TO STRONG
POLEWARD OUTFLOW INTO THE AFOREMENTION MIDLATITUDE TROUGH. THE
SYSTEM SHOULD PEAK AT 115 KNOTS BY TAU 72 DUE TO VERY FAVORABLE
ENVIRONMENTAL CONDITIONS. AFTER TAU 72, TD 27W WILL TRACK
NORTH-NORTHEASTWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE
STR THROUGH TAU 120. AFTER TAU 72, STEADY WEAKENING WILL OCCUR AS
VERTICAL WIND SHEAR INCREASES TO 25 TO 30 KNOTS.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 72 WITH THE EXCEPTION OF NAVGEM, THE SOLE OUTLIER,
WHICH TRACKS THE SYSTEM WESTWARD THEN SLOWLY NORTH-NORTHWESTWARD.
AFTER TAU 72, THERE IS A HIGH DEGREE OF UNCERTAINTY (LOW
CONFIDENCE) IN THE JTWC FORECAST TRACK. SEVERAL MODELS (GFS, GFS
ENSEMBLE MEAN, UKMET ENSEMBLE MEAN) INDICATE THE SYSTEM WILL SLOW
AND STALL AS A LOW-LEVEL RIDGE BUILDS TO THE NORTH AND A FRONTAL
SYSTEM RAPIDLY PUSHES EASTWARD. THE GFS ENSEMBLE (GEFS) SHOWS A
BIFURCATION WITH THE BULK OF THE SOLUTIONS STALLING AND TRACKING
TOWARD AND OVER THE PHILIPPINES AFTER TAU 120. THE ECMWF
DETERMINISTIC SOLUTION DEPICTS A RAPID NORTH-NORTHEASTWARD TRACK AND
IS THE FASTEST MODEL AT THIS TIME. THE ECMWF ENSEMBLE AT 290600Z,
HOWEVER, SHOWS ONLY A FEW SOLUTIONS WITH A SIMILAR FAST POLEWARD
TRACK. THE BULK OF THE EPS SOLUTIONS ARE STALLING AND SLOWING
BETWEEN 21N AND 24N. THE ECMWF DETERMINISTIC SOLUTION APPEARS
UNLIKELY DUE TO THE BUILDING RIDGE TO THE NORTH AND LACK OF A
FRONTAL SYSTEM SO THE JTWC FORECAST FAVORS THE GFS DETERMINISTIC
MODEL SOLUTION AT THIS TIME.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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