WTPA44 PHFO 060900 TCDCP4 TROPICAL STORM JIMENA DISCUSSION NUMBER 43 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP132015 1100 PM HST SAT SEP 05 2015 JIMENA CONTINUES TO BE EMBEDDED WITHIN A RATHER HARSH ENVIRONMENT... CHARACTERIZED BY SIGNIFICANT /NEAR 25 KT PER UW-CIMSS ANALYSIS/ SOUTHWESTERLY VERTICAL WIND SHEAR THAT IS HELPING TO ENTRAIN DRY MID- AND UPPER-LEVEL AIR INTO THE CIRCULATION. SATELLITE IMAGERY SHOWS SEVERELY RESTRICTED OUTFLOW IN THE SOUTHWEST SEMICIRCLE...WITH A CURVED BAND OF DEEP CONVECTION WRAPPING IN TOWARD THE CENTER FROM THE NORTH. RECENT MICROWAVE OVERPASSES INCLUDE A RECENTLY ARRIVED 0526Z SSMIS IMAGE AS WELL AS A 0326Z SSMIS IMAGE...BOTH OF WHICH SHOW THAT THE LOW LEVEL CIRCULATION CENTER /LLCC/ IS BECOMING DETACHED FROM THE UPPER LEVEL CIRCULATION...WITH THE SYSTEM TILTED TOWARD THE NORTH-NORTHEAST WITH HEIGHT. LATEST DVORAK CURRENT INTENSITY /CI/ ESTIMATES WERE 3.5/55 KT FROM PHFO AND PGTW...WHILE SAB INDICATED 3.0/45 KT. ADT CI VALUES FROM UW-CIMSS HAVE BEEN RIGHT AROUND 3.2/49 KT FOR THE PAST COUPLE OF HOURS. A BLEND OF THE INTENSITY ESTIMATES LEADS TO AN INITIAL INTENSITY OF 50 KT FOR THIS ADVISORY...THUS INDICATING THAT JIMENA HAS RAPIDLY WEAKENED OVER THE PAST 24 HOURS. THE LLCC IS ESTIMATED TO BE ON THE SOUTHWEST SIDE OF THE DIMINISHING COLD CLOUD CANOPY...AND THE INITIAL MOTION FOR THIS PACKAGE IS 325/07 KT. THERE IS A GREATER THAN NORMAL AMOUNT OF UNCERTAINTY IN THE INITIAL MOTION ESTIMATE...AS THE LLCC IS SOMEWHAT DIFFICULT TO PINPOINT...AND THE AFOREMENTIONED 0526Z SSMIS IMAGE SUGGESTS THAT THE INITIAL POSITION FOR THIS PACKAGE MAY HAVE BEEN A LITTLE TOO FAR TO THE SOUTHWEST. JIMENA CONTINUES TO MOVE BETWEEN A MID-LEVEL RIDGE THAT EXTENDS FROM NORTH THROUGH EAST THROUGH SOUTHEAST OF THE SYSTEM...TOWARD A TROUGH TO THE NORTHWEST. AFTER ABOUT 36 HOURS... THE RIDGE TO THE NORTH IS FORECAST TO BRIEFLY STRENGTHEN BEFORE THEN BUILDING TO THE WEST AND NORTHWEST OF JIMENA. THIS WILL RESULT IN A TURN TOWARD THE WEST...WITH THE AMOUNT OF TURN VARYING AMONG THE DIFFERENT MODELS...PRIMARILY DUE TO DIFFERENCES IN THE STRENGTH AND POSITION OF THE BUILDING RIDGE. THE UPDATED TRACK FORECAST FOLLOWS THE TRAJECTORY OF THE PREVIOUS VERY CLOSELY...BUT IS FASTER AND TO THE RIGHT THROUGH 48 HOURS...AND THEN VERY CLOSE...BUT JUST NORTH OF THE PREVIOUS THROUGH DAY 5. WHILE THE OFFICIAL TRACK FORECAST HAD BEEN ON THE SOUTH SIDE OF A GUIDANCE ENVELOPE THAT SHOWS INCREASING SPREAD IN THE LATER PERIODS...IT NOW LIES BETWEEN THE TVCN AND GFEX CONSENSUS...AS THE LATEST ECMWF BUILDS A STRONGER RIDGE TO THE WEST OF JIMENA...THEREBY IMPARTING A SOUTHWESTERLY MOTION TO THE CYCLONE ON DAYS 3 THROUGH 5. PERSISTENT AND RELATIVELY STRONG SHEAR...FIRST FROM THE SOUTHWEST... AND THEN FROM THE WEST AND NORTHWEST...IS EXPECTED TO LEAD TO THE EVENTUAL DEMISE OF JIMENA. A BRIEF RELAXATION OF THE SHEAR IS POSSIBLE ON SUNDAY...AND THUS THE WEAKENING TREND IS FORECAST TO ABATE BRIEFLY...UNTIL SHEAR INCREASES AGAIN THEREAFTER. GIVEN THAT THE RECENT RATE OF WEAKENING HAS BEEN WELL ANTICIPATED BY SHIPS GUIDANCE...AND LESS SO BY OTHER MEMBERS OF THE INTENSITY CONSENSUS IVCN...THE UPDATED INTENSITY FORECAST HAS GIVEN ADDITIONAL WEIGHT TO SHIPS. THIS IS ESPECIALLY TRUE IN THE LATER PERIODS WHERE IVCN INDICATES RE-STRENGTHENING DUE TO CONTRIBUTIONS FROM THE GFDL...WHICH BRINGS JIMENA BACK NEAR HURRICANE STRENGTH ON DAY 5. THE OFFICIAL INTENSITY FORECAST REMAINS A LITTLE CONSERVATIVE IN THAT IT MAINTAINS A VIABLE TROPICAL CYCLONE THROUGH DAY 4...WHEREAS SHIPS DISSIPATES JIMENA AFTER 60 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 22.9N 147.9W 50 KT 60 MPH 12H 06/1800Z 23.9N 148.7W 45 KT 50 MPH 24H 07/0600Z 24.8N 149.9W 45 KT 50 MPH 36H 07/1800Z 25.4N 151.1W 40 KT 45 MPH 48H 08/0600Z 25.6N 152.3W 35 KT 40 MPH 72H 09/0600Z 25.2N 155.5W 30 KT 35 MPH 96H 10/0600Z 25.0N 159.0W 30 KT 35 MPH 120H 11/0600Z 25.0N 162.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER BIRCHARD