ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM NICHOLAS DISCUSSION NUMBER 16 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT FRI OCT 17 2003 SATELLITE IMAGERY SHOWS THAT NICHOLAS IS SLOWLY ORGANIZING...WITH A CENTRAL DENSE OVERCAST AND SOME OUTER BANDING IN THE EASTERN SEMICIRCLE. HOWEVER...AN SSM/I OVERPASS AT 0952Z SHOWED LINEAR CONVECTION IN THE OVERCAST AND A LOW-LEVEL CENTER EXPOSED SOUTH OF THE CONVECTION. SATELLITE INTENSITY ESTIMATES HAVE UNANIMOUSLY INCREASED TO 65 KT. GIVEN THE MICROWAVE DATA...NICHOLAS WILL REMAIN A TROPICAL STORM AT THIS TIME WITH 60 KT MAXIMUM WINDS. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 320/8. VISIBLE IMAGERY AND SURFACE OBSERVATIONS INDICATE A WEAK LOW/MID-LEVEL RIDGE NORTH OF NICHOLAS. WATER VAPOR IMAGERY SHOWS A BROAD UPPER-LEVEL RIDGE ALONG 41W/42W S OF 22N...AND A STREAM OF SHORTWAVE TROUGHS AND RIDGES IN THE WESTERLIES N OF 21N W OF 44W. THIS COMPLEX PATTERN IS PRODUCING WEAK STEERING CURRENTS...AND THE TRACK GUIDANCE RESPONDS TO THIS BY GENERALLY FORECASTING A SLOW NORTHWESTWARD OR NORTH-NORTHWESTWARD MOTION. THERE IS BETTER AGREEMENT BETWEEN THE DYNAMICAL MODELS THAN 24 HR AGO...AS THE NOGAPS HAS SHIFTED WESTWARD FROM ITS PREVIOUS FORECASTS. HOWEVER...THERE ARE STILL OUTLIERS SUCH AS THE EASTWARD LBAR AND THE WESTWARD BAMS. THE FORECAST TRACK CALLS FOR A SLOW NORTHWESTWARD MOTION DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE...AND IS NUDGED A LITTLE TO THE RIGHT OF THE PREVIOUS PACKAGE. THE UPPER-LEVEL RIDGE SOUTHEAST OF NICHOLAS HAS A WELL-DEFINED WIND MAXIMUM ALONG ITS NORTHERN PERIPHERY. THIS WIND BAND IS CURRENTLY CLOSE TO NICHOLAS AND IS CAUSING SOUTHWESTERLY SHEAR. THE FUTURE INTENSITY DEPENDS ON HOW CLOSE THE STORM STAYS TO THE WIND MAXIMUM. DYNAMICAL MODELS FORECAST THE RIDGE TO MOVE WESTWARD...WHICH COULD FORCE THE WIND MAXIMUM NORTH OF THE CYCLONE AND CREATE A MORE FAVORABLE ENVIRONMENT DURING THE NEXT 48 HR...ESPECIALLY IF NICHOLAS MOVES SLOWER THAN FORECAST. CONVERSELY...IF THE STORM MOVES FASTER THAN FORECAST...IT WOULD REMAIN IN STRONGER SHEAR. THE SHIPS MODEL CALLS FOR STEADY WEAKENING THROUGH THE FORECAST PERIOD UNDER MODERATE TO STRONG SHEAR...WHICH SEEMINGLY DOES NOT MATCH EITHER CURRENT TRENDS OR THE MODEL UPPER-LEVEL WINDS FORECASTS. THE LOW-CONFIDENCE INTENSITY FORECAST CALLS FOR A LITTLE MORE STRENGTHENING IN ANTICIPATION OF SOME DECREASE IN THE SHEAR...FOLLOWED BY WEAKENING AFTER 48 HR AS NICHOLAS ENCOUNTERS STRONGER WESTERLIES ALONG AND NORTH OF 20N. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 17/1500Z 16.0N 48.3W 60 KT 12HR VT 18/0000Z 16.9N 48.8W 65 KT 24HR VT 18/1200Z 17.7N 49.3W 65 KT 36HR VT 19/0000Z 18.4N 49.9W 65 KT 48HR VT 19/1200Z 19.1N 50.6W 65 KT 72HR VT 20/1200Z 20.0N 51.5W 60 KT 96HR VT 21/1200Z 21.5N 52.5W 55 KT 120HR VT 22/1200Z 22.5N 53.5W 45 KT NNNN
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Page last modified: Monday, 07-Feb-2005 16:50:00 UTC