Tropical Storm RAI Advisory sáb, 18-12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (RAI) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 10.2N 119.2E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 278 NM SOUTH-SOUTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS BROAD AREA
OF CONVECTION MOVING THROUGH THE SULU SEA. FOR A FEW FRAMES OF THE
MSI LOOP, THERE APPEARED TO BE A NEW EYE TRYING TO FORM, HOWEVER,
THE CONVECTIVE MASS IS NOW MORE ORGANIZED AND SURROUNDS THE MAIN
LLCC. A VIVID MICROWAVE EYE FEATURE IS EASILY IDENTIFIABLE ON THE
170546Z AMSR2 36GHZ AND 89GHZ COLOR COMPOSITE IMAGES LENDING TO
HIGH CONFIDENCE FOR THE INITIAL POSITION. THE INITIAL INTENSITY IS
SET WITH MEDIUM CONFIDENCE AND HEDGED SLIGHTLY HIGHER THAN ADT AT
82KTS, SATCON AT 87KTS, AND IS MORE IN LINE WITH THE VAST MAJORITY
OF DVORAK CURRENT INTENSITY ESTIMATES LYING BETWEEN T4.5(77KTS) AND
T5.5(102KTS). ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, WITH WARM
SSTS, MODERATE EASTERLY SHEAR AND GOOD WESTWARD AND POLEWARD
OUTFLOW.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 80 KTS AT 170147Z
   CIMSS ADT: 84 KTS AT 170540Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG WESTWARD
   OTHER FACTORS: MODERATE POLEWARD AND EQUATORWARD OUTFLOW.
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.
FORECAST DISCUSSION: TY 28W HAS CONTINUED TO DEGRADE OVER THE PAST
FEW HOURS, AND IS MOVING BACK OVER THE NORTHERN PORTION OF THE WARM
SULU SEA. IT WILL CONTINUE TO MOVE WESTWARD OVER NORTHERN PALAWAN
ISLAND. THE PASSAGE OVER PALAWAN IS EXPECTED TO HAVE LITTLE IN THE
WAY OF IMPACT ON THE INTENSITY. ONCE IN THE SOUTH CHINA SEA, THE
SYSTEM WILL BEGIN TO DEEPEN AND INTENSIFY AS THE SYSTEM CONTINUES
MOVING WESTWARD OVER THE WARM WATERS. AN UPPER-LEVEL ANTICYCLONE IS
EXPECTED TO FORM OVER THE SYSTEM, BOTH REDUCING THE VWS AND
INCREASING THE AVAILABLE OUTFLOW, WHICH WILL ALSO REACH INTO THE
SOUTHERN REACHES OF THE MID-LATITUDE WESTERLIES. THE INCREASED
OUTFLOW AND WARM SSTS WILL HELP THE SYSTEM REACH A PEAK OF 105
KNOTS BY TAU 24. THEREAFTER, THE SYSTEM WILL THEN GRADUALLY TURN
MORE NORTHWESTWARD WITH EACH PASSING HOUR AND BY TAU 48, IT WILL
TURN SHARPLY POLEWARD AS IT ROUNDS THE STR AS THE RIDGE RETREATS
EASTWARD. SHORTLY AFTER TAU 48, THE SYSTEM WILL ENCOUNTER COOLER
SSTS AND BEGIN TO WEAKEN RAPIDLY AS THE SURGE FROM THE NORTHEAST
WILL INCREASE VWS AND EXPOSE THE LOW-LEVEL CIRCULATION. THE SYSTEM
WILL FULLY DISSIPATE OVER THE WATER BY TAU 120, TURNING
EAST-SOUTHEASTWARD FOLLOWING THE LOW-LEVEL FLOW PATTERN SOUTHEAST
OF HONG KONG.
MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH
TAU 72, WITH A MODEST SPREAD OF ONLY 160NM AT THIS TIME. AS THE
SYSTEM RECURVES THE GUIDANCE SPREADS BUT REMAINS IN RELATIVELY GOOD
AGREEMENT, WITH THE SPREAD ONLY INCREASING 20NM AT TAU 96, THEN
QUICKLY INCREASING TO 280NM AT TAU 120. THE BULK OF THE GUIDANCE IS
CONSTRAINED WITHIN A TIGHT ENVELOPE THROUGH THE FORECAST PERIOD,
HOWEVER, JGSM LOSES THE SYSTEM OVER HAINAN, WHILE GALWEM CARRIES
THE SYSTEM JUST SOUTH OF HONG KONG. THE JTWC FORECAST LIES ALONG
THE NORTHERN SIDE OF THE ENVELOPE THROUGH TAU 48, THEN ON THE
INSIDE OF THE RECURVE TRACK THROUGH TAU 120. CONFIDENCE IS HIGH
THROUGH TAU 72, THEN LOW THEREAFTER AS THE RATE OF WEAKENING WILL
HAVE A LARGE IMPACT ON THE ULTIMATE TRACK. INTENSITY GUIDANCE IS IN
AGREEMENT ON THE OVERALL INTENSIFICATION AND WEAKENING TREND, BUT
DEPICTS FAIRLY LARGE DIFFERENCES IN THE ACTUAL INTENSITIES. THE
JTWC FORECAST CLOSELY TRACKS THE COAMPS-TC AND HWRF THROUGH TAU 48,
AND THEN FALLS MORE IN LINE WITH THE CONSENSUS MEAN THROUGH THE
REMAINDER OF THE FORECAST. UNCERTAINTY REMAINS HIGH THROUGH THE
FORECAST, AS THE ULTIMATE INTENSITY RELIES UPON HOW QUICK THE
SYSTEM WILL INTENSIFY IN THE SOUTH CHINA SEA. THUS THERE IS LOW
CONFIDENCE IN THE JTWC INTENSITY FORECAST.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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