HURRICANE NORBERT DISCUSSION NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008
800 AM PDT WED OCT 08 2008
NORBERT UNDERWENT RAPID INTENSIFICATION OVERNIGHT...AND THE CYCLONE
NOW HAS AN IMPRESSIVE SATELLITE PRESENTATION CONSISTING OF A
WELL-DEFINED EYE SURROUNDED BY A RING OF VERY DEEP CONVECTION. THE
INITIAL INTENSITY IS INCREASED TO 110 KT BASED ON A COMPROMISE
BETWEEN THE SUBJECTIVE DVORAK ESTIMATES OF 102 KT AND OBJECTIVE
DVORAK ESTIMATES NEAR 125 KT. WITH THE LARGE-SCALE ENVIRONMENT
EXPECTED TO REMAIN FAVORABLE FOR ANOTHER DAY OR SO...INTENSITY
WILL BE LARGELY CONTROLLED BY THE INNER-CORE STRUCTURAL EVOLUTION
IN THE SHORT-TERM. FORECASTING SUCH INNER-CORE CHANGES IS
DIFFICULT BUT GUIDANCE SUGGEST THAT NORBERT COULD GET A LITTLE
STRONGER...PERHAPS REACHING CATEGORY 4 STRENGTH. IN ABOUT 36-48
HOURS...VERTICAL SHEAR IS FORECAST TO INCREASE AND SSTS GRADUALLY
DECREASE ALONG THE FORECAST TRACK. ADDITIONALLY...NORBERT COULD BE
NEGATIVELY IMPACTED BY RELATIVELY STABLE AIR TO ITS NORTHWEST.
STILL...NORBERT COULD APPROACH BAJA CALIFORNIA AS A HURRICANE...AND
INTERESTS OVER THE CENTRAL AND SOUTHERN PORTIONS OF THE PENINSULA
SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.
NORBERT CONTINUES TO MOVE AROUND A STRONG RIDGE OVER THE
SOUTHWESTERN UNITED STATES RESULTING IN A WEST-NORTHWEST HEADING...
OR 290 DEGREES AT 8 KNOTS. A GRADUAL TURN TOWARD THE NORTHWEST IS
EXPECTED DURING THE NEXT TWO DAYS AS THE CYCLONE REACHES THE
WESTERN PERIPHERY OF THE RIDGE. THEREAFTER...A TURN TOWARD THE
NORTH AND NORTHEAST WITH AN INCREASE IN FORWARD SPEED IS EXPECTED
AS A LARGE MID-LATITUDE TROUGH DEVELOPS OVER THE WESTERN UNITED
STATES AND ADJACENT PACIFIC. WHILE ALL OF THE DYNAMICAL MODELS
FORECAST THIS TROUGH TO DEVELOP...THEY DISAGREE SOMEWHAT ON
NORBERT'S STRENGTH...AND HENCE ITS VERTICAL DEPTH...WHEN IT REACHES
THE TROUGH. MOST OF THE TRACK MODEL SHOW A DEEP CYCLONE RESPONDING
TO THE TROUGH BY ACCELERATING NORTHEASTWARD IN ABOUT 3 DAYS.
HOWEVER...THE GFS AND THE ECMWF MODELS STILL SHOW NORBERT RAPIDLY
BECOMING A SHALLOW SYSTEM AS IT NEARS THE BAJA PENINSULA RESULTING
IN A REDUCTION IN FORWARD SPEED OR EVEN STALLING IN THE VICINITY OF
BAJA CALIFORNIA. SINCE THESE HIGHLY-RESPECTED MODELS CANNOT BE
IGNORED...THE OFFICIAL FORECAST IS A LITTLE SLOWER THAN THE
DYNAMICAL MODEL CONSENSUS AT DAY 4.
