000
WTPZ41 KNHC 171442
TCDEP1
 
TROPICAL STORM FERNANDA DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP062011
800 AM PDT WED AUG 17 2011
 
FERNANDA HAS A SOMEWHAT HOLLOW APPEARANCE. THE EXTENT AND DEPTH OF
ITS CONVECTION HAS BEEN DECREASING...POSSIBLY IN RESPONSE TO THE
INGESTION OF A DRIER AND MORE STABLE AIR MASS FROM THE NORTH.
WHATEVER REMAINING CONVECTION IS IN A BAND WRAPPING AROUND THE
SOUTHERN SEMICIRCLE.  HOWEVER...SEVERAL MICROWAVE PASSES HAVE
INDICATED NO SIGNIFICANT CHANGE IN THE CENTRAL FEATURES OF THE
STORM...WITH A WELL DEFINED CIRCULATION AND OUTFLOW THAT REMAINS
WELL ESTABLISHED.  CURRENT CI NUMBERS REMAIN AT 3.0...SO THE
INITIAL INTENSITY IS HELD AT 45 KT.
 
THE INITIAL MOTION ESTIMATE IS 275/08...WITH RECENT FIXES
POSSIBLY SUGGESTING A MOTION SLIGHTLY TO THE RIGHT.  FERNANDA IS
APPROACHING THE WESTERN END OF A SUBTROPICAL RIDGE. A LONGWAVE
TROUGH ALONG 140W IS FORECAST TO LIFT OUT DURING THE NEXT COUPLE OF
DAYS...LEAVING A WEAKNESS IN ITS WAKE.  GLOBAL MODELS SHOW THE
TRACK OF FERNANDA TURNING WEST-NORTHWESTWARD IN RESPONSE TO THE
WEAKNESS BUT THEN BENDING TOWARD THE WEST AS THE CYCLONE WEAKENS
AND FERNANDA GETS CAUGHT UNDER A LOW-/MID-LEVEL RIDGE. THERE IS A
FAIR AMOUNT OF SPREAD IN THE GUIDANCE...WITH THE GFS/HWRF/GFDL
FAVORING A MORE SIGNIFICANT WEAKNESS AND MORE NORTHWARD FORECAST
TRACKS.  THE UKMET/ECMWF SHOW STRONGER RIDGING AND ARE ON THE
SOUTHERN EDGE OF THE GUIDANCE ENVELOPE.  THE OFFICIAL NHC TRACK HAS
CHANGED LITTLE SINCE THE LAST ADVISORY AND IS GENERALLY IN THE
MIDDLE OF THESE TWO CAMPS...TO THE LEFT OF THE MULTI-MODEL
CONSENSUS TVCE.
 
THE SHIPS MODEL SHOWS FERNANDA EMBEDDED IN A LOW SHEAR ENVIRONMENT
DURING THE NEXT 48 HOURS. HOWEVER...SEA SURFACE TEMPERATURES
DECREASE ALONG THE PATH OF THE STORM...ALBEIT SLOWLY...AND FERNANDA
IS LIKELY TO CONTINUE INGESTING A DRIER AND MORE STABLE AIR MASS
FROM THE NORTH AND WEST. THESE FACTORS SUGGEST THAT THE CYCLONE
SHOULD ESSENTIALLY MAINTAIN ITS STRENGTH DURING THE NEXT DAY OR TWO.
AFTER THAT...INCREASING SHEAR RELATED TO A UPPER-LEVEL CYCLONIC
SHEAR AXIS SOUTH OF HAWAII AND EVEN COOLER WATERS SHOULD RESULT IN
A WEAKENING TREND.  THE OFFICIAL NHC FORECAST IS SIMILAR TO THE
PREVIOUS ONE AND IS FAIRLY CLOSE TO THE STATISTICAL-DYNAMICAL MODEL
CONSENSUS.
 
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/1500Z 11.8N 137.8W   45 KT  50 MPH
 12H  18/0000Z 12.2N 138.9W   50 KT  60 MPH
 24H  18/1200Z 13.0N 140.3W   50 KT  60 MPH
 36H  19/0000Z 14.0N 142.0W   45 KT  50 MPH
 48H  19/1200Z 14.9N 143.7W   45 KT  50 MPH
 72H  20/1200Z 15.2N 146.2W   35 KT  40 MPH
 96H  21/1200Z 16.5N 151.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  22/1200Z 16.5N 155.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
FORECASTER KIMBERLAIN