#356 Postby cycloneye » Sun Sep 06, 2015 4:58 am
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
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