Tropical Storm YAMANEKO Advisory 11月13日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (YAMANEKO) WARNING
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 21.8N 165.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 158 NM NORTH-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
ASYMMETRIC SYSTEM, WITH AN ELONGATED AREA OF MODERATE CONVECTION
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). A 121755Z SSMIS
COLOR ENHANCED 91GHZ MICROWAVE IMAGE SHOWED AN AREA OF MODERATE
CONVECTION WHICH IS ELONGATED DOWN THE SHEAR VECTOR TOWARDS THE
NORTHEAST, FLARING CONVECTION EXTENDING IN A CURVED BAND TO THE
SOUTHWEST OVER WAKE ISLAND AND SHALLOW BANDING FEATURES WHICH ARE
WRAPPING INTO A WEAK LLCC DISPLACED TO THE SOUTHWEST. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE MICROWAVE
IMAGE DESCRIBED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE, HEDGED TOWARDS THE HIGHER END OF THE AGENCY
DVORAK CURRENT INTENSITY ESTIMATES FROM PGTW, PHFO AND KNES. THE
ENVIRONMENT IS MARGINAL AT BEST, WITH MODERATE TO HIGH VWS
IMPINGING THE SYSTEM FROM THE WEST. CIMSS ANALYSIS SUGGESTS 30 KNOT
OR HIGHER SHEAR, BUT THE SATELLITE DEPICTION WOULD SUGGEST A
SLIGHTLY LOWER VALUE BUT REGARDLESS IT IS RELATIVELY HIGH. THE
OTHER ENVIRONMENTAL FACTORS ARE SUPPORTIVE FOR DEVELOPMENT, WITH
SSTS REMAINING ABOVE 26C AND ROBUST POLEWARD OUTFLOW PROVIDED
BY A SMALL POINT SOURCE CENTERED JUST EAST OF THE SYSTEM. TS 28W IS
MOVING NORTHWARD ALONG THE WESTERN SIDE OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR THE DATELINE.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 30 KTS AT 121458Z
   CIMSS ADT: 32 KTS AT 121740Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING. THE FORECAST HAS BEEN
TRUNCATED TO 48 HOURS, AT WHICH POINT THE SYSTEM WILL TRANSITION TO
AN EXTRA-TROPICAL CYCLONE.
FORECAST DISCUSSION: HAVING QUICKLY FORMED OVERNIGHT, TROPICAL
STORM (TS) 28W HAS BEEN ABLE TO CONSOLIDATE A LOW LEVEL CORE, EVEN
IN THE FACE OF A MARGINAL ENVIRONMENT WITH RELATIVELY HIGH SHEAR.
CONVECTION HSA BEEN ABLE TO PERSIST, AND THIS IS PUSHING BACK ON
THE SHEAR JUST ENOUGH TO ALLOW FOR A SMALL AMOUNT OF
INTENSIFICATION OVER THE PAST FEW HOURS. THE SYSTEM IS MOVING NORTH
AT A RELATIVELY SLOW PACE, ALONG THE WESTERN SIDE OF THE DEEP RIDGE
CENTERED NEAR THE DATELINE. HOWEVER, TRACK MOTION IS EXPECTED TO
SLOW AND TURN A BIT TO THE NORTHWEST IN THE NEAR-TERM AS THE
LOW-LEVEL FLOW IS DOMINATED BY A TRANSITORY RIDGE PASSING BY TO THE
NORTH. AROUND TAU 24, THE RIDGE TO THE NORTH WILL MOVE TO A
POSITION EAST OF DUE NORTH OF TS 28W, AND THE SYSTEM WILL QUICKLY
TURN NORTHEAST AND ACCELERATE ALONG THE TIGHT GRADIENT BETWEEN THIS
TRANSITORY RIDGE AND AN APPROACHING LOW PRESSURE SYSTEM AND
ASSOCIATED LOW-LEVEL FRONT AND UPPER-LEVEL TROUGH. SOME ADDITIONAL
NEAR-TERM INTENSIFICATION IS POSSIBLE AS THE SYSTEM CONTINUES TO
TAP INTO THE STRONGLY DIVERGENT UPPER-LEVEL POLEWARD OUTFLOW. AFTER
TAU 24 THE SYSTEM WILL START TO FEEL THE EFFECTS OF SHARPLY
INCREASED SHEAR BUT WILL STILL HAVE ACCESS TO VERY STRONG POLEWARD
OUTFLOW AND THE TWO WILL OFFSET FOR TIME, ALLOWING FOR THE SYSTEM
TO MAINTAIN TS STRENGTH THROUGH THE END OF THE FORECAST. A DEEP
TROUGH CURRENTLY MOVING OFF THE COAST OF JAPAN WILL BECOME
NEGATIVELY TILTED OVER THE NEXT 24 HOURS AS IT MOVES FURTHER EAST.
TS 28W WILL MOVE INTO PHASE WITH THIS NEGATIVELY TILTED TROUGH
AROUND TAU 36, MARKING THE ONSET OF A VERY RAPID EXTRA-TROPICAL
TRANSITION (ETT). THE SYSTEM IS FORECAST TO COMPLETE ETT NO LATER
THAN TAU 48 AS A WARM SECLUSION TYPE SYSTEM. ADDITIONAL
INTENSIFICATION IS POSSIBLE AFTER ETT AND BEYOND THE FORECAST
PERIOD AS THE SYSTEM RACES OFF THE NORTHEAST.
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT THROUGH THE FORECAST PERIOD, WITH MINIMAL
CROSS-TRACK DEVIATION BETWEEN THE VARIOUS MODELS. ALONG-TRACK
SPREAD INCREASES MARGINALLY BY TAU 48 AS THE SYSTEM UNDERGOES ETT
AND SOME OF THE MODELS LOSE THE VORTEX. THE JTWC TRACK LIES AMONGST
THE MODEL PACK, NEAR THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH THE
HWRF PEAKING THE SYSTEM AT 50 KNOTS IN 12 HOURS, WHILE THE
DECAY-SHIPS KEEP THE SYSTEM AT OR BELOW 40 KNOTS, WHILE ALL MODELS
SHOW A POST-FORECAST INTENSIFICATION AFTER ETT. THE JTWC FORECAST
LIES JUST BELOW THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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