000 WTPZ45 KNHC 051439 TCDEP5 TROPICAL STORM NORBERT DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152008 800 AM PDT SUN OCT 05 2008 NORBERT'S CLOUD PATTERN CONTINUES TO SHOW AN INCREASE IN ORGANIZATION WITH THE CENTER NOW SITUATED BENEATH A CDO FEATURE. DVORAK SATELLITE INTENSITY ESTIMATES HAVE INCREASED TO 45 KT FROM BOTH TAFB AND SAB BUT THE INITIAL INTENSITY IS SET SLIGHTLY HIGHER...AT 50 KT...AS A COMPROMISE BETWEEN THE AFOREMENTIONED SUBJECTIVE DVORAK ESTIMATES AND OBJECTIVE ESTIMATES FROM THE UNIVERSITY OF WISCONSIN. NORBERT IS EXPECTED TO BE OVER WARM WATERS AND WITHIN A RELATIVELY LOW VERTICAL SHEAR ENVIRONMENT FOR THE NEXT COUPLE OF DAYS SO FURTHER INTENSIFICATION IS ANTICIPATED. HOWEVER...THE AMOUNT OF INTENSIFICATION REMAINS UNCLEAR WITH A SPREAD OF NEARLY 55 KT IN THE VARIOUS INTENSITY MODELS AT DAY 3. FURTHER COMPLICATING THE INTENSITY FORECAST IS THE UNCERTAINTY IN FORWARD SPEED THAT ARISES AT THE EXTENDED PERIODS AS NORBERT APPROACHES COOLERS WATERS AND A STABLE AIRMASS NORTH OF 20 DEGREES NORTH LATITUDE. GIVEN THE PRESENT TREND IN SATELLITE IMAGERY...THE OFFICIAL FORECAST SHOWS NORBERT REACHING PEAK INTENSITY SOONER THAN THE PREVIOUS ADVISORY AND IS IN CLOSEST AGREEMENT WITH THE LGEM AND GFDL MODELS. THERE HAVE BEEN NO RECENT MICROWAVE PASSES RESULTING IN A SOMEWHAT UNCERTAIN CENTER POSITION ESTIMATE. SINCE THE OVERALL CLOUD MASS APPEARS TO BE MOVING MORE TOWARDS THE WEST-NORTHWEST...THE INITIAL MOTION IS NOW ESTIMATED TO BE 290/7. A LARGE DEEP-LAYER TROUGH IS CURRENTLY MOVING EASTWARD OVER THE WESTERN HALF OF THE U.S. WITH A NARROW SLIVER OF A MID-LEVEL RIDGE EXTENDING WESTWARD FROM MEXICO JUST TO NORTH OF NORBERT. THE SHORT-TERM TRACK WILL BE DICTATED BY WHETHER OR NOT THIS NARROW RIDGE REMAINS IN PLACE AS THE LARGER TROUGH PASSES TO THE NORTH. MOST OF THE DYNAMICAL MODELS MAINTAIN SUFFICIENT RIDGING TO THE NORTH TO KEEP THE CYCLONE ON A GENERAL WEST-NORTHWESTWARD HEADING FOR 2-3 DAYS. ONLY THE UKMET MODEL SHOWS THE RIDGE BREAKING DOWN ALLOWING NORBERT TO TRACK MORE TOWARDS THE NORTH...CLOSER TO THE COAST OF MEXICO. BY DAYS 4 AND 5...GLOBAL MODELS ALL FORECAST A MIDDLE TO UPPER-LEVEL CUTOFF LOW TO FORM SEVERAL HUNDRED MILES WEST OF THE BAJA PENINSULA... RESULTING IN THE CYCLONE TURNING TOWARD THE NORTHWEST OR NORTH. HOWEVER...THE MODELS HAVE CONSIDERABLE SPREAD IN FORWARD SPEED AT THESE EXTENDED RANGES. FORECAST POSITIONS AND MAX WINDS INITIAL 05/1500Z 14.6N 101.9W 50 KT 12HR VT 06/0000Z 14.8N 102.8W 60 KT 24HR VT 06/1200Z 15.2N 104.0W 65 KT 36HR VT 07/0000Z 15.6N 105.1W 70 KT 48HR VT 07/1200Z 16.1N 106.3W 75 KT 72HR VT 08/1200Z 17.0N 108.5W 75 KT 96HR VT 09/1200Z 19.0N 111.0W 70 KT 120HR VT 10/1200Z 21.5N 112.5W 65 KT $$ FORECASTER RHOME