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| #101672 (Received by flhurricane at: 5:34 AM 02.Aug.2006) TCDAT3 TROPICAL STORM CHRIS DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032006 500 AM EDT WED AUG 02 2006 AIR FORCE RESERVE RECON POSITION AND WIND DATA THIS MORNING...ALONG WITH NOAA DOPPLER RADAR DATA FROM SAN JUAN AND SATELLITE IMAGERY... INDICATE CHRIS HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 6 HOURS. AN UPPER-LEVEL EYE FEATURE HAS BECOME APPARENT IN RADAR IMAGERY...ALTHOUGH IT IS TILTED ABOUT 12 NMI TO THE SOUTHWEST OF THE LOW-LEVEL CENTER. WHILE THE STRUCTURE OF CHRIS HAS IMRPOVED... THIS HAS NOT TRANSLATED INTO AN INCREASE IN INTENSITY...YET. A PASS THROUGH THE CENTER OF CHRIS AROUND 0745Z REVEALED AN ESTIMATED CENTRAL PRESSURE OF 1001 MB AND AN 850 MB FLIGHT-LEVEL WIND OF 62 KT. WHILE THE PRESSURE IS DOWN 2 MB FORM EARLIER FLIGHTS...THE FLIGHT-LEVEL WINDS STILL YIELD ONLY A 50-KT SURFACE WIND. UPPER-LEVEL OUTFLOW HAS IMPROVED IN ALL QUADRANTS...AND THE OVERALL CONVECTIVE STRUCTURE AS BECOME MORE SYMMETRICAL. THE MOTION ESTIMATE IS 300/09 KT...ALTHOUGH THE SHORT TERM MOTION FROM THE LAST SEVERAL RECON FIXES YIELDS A MOTION OF 310/11. OVERALL...NO SIGNIFICANT CHANGE TO THE STRENGTH AND POSITION OF THE BERMUDA HIGH PRESSURE RIDGE TO THE NORTH OF CHRIS IS FORECAST BY THE GLOBAL MODELS. THE RIDGE AXIS CURRENTLY EXTENDS WESTWARD ACROSS THE SOUTHEASTERN U.S. AND INTO THE U.S. CENTRAL PLAINS...AND IS EXPECTED TO REMAIN IN ROUGHLY THAT POSITION THROUGHOUT THE FORECAST PERIOD. THERE ARE SIGNIFICANT DIFFERENCES NOW IN HOW THE MODELS HANDLE THE STRENGTH OF CHRIS. UNLIKE PREVIOUS RUNS OVER THE PAST FEW DAYS...MOST OF THE GLOBAL MODELS...ESPECIALLY NOGAPS...NOW HANG ONTO CHRIS AS A TROPICAL CYCLONE...ALBEIT A SMALL COMPACT ONE. THE GFS...GFS ENSEMBLE...NOGAPS...AND UKMET MODELS HAVE MADE A SIGNIFICANT NORTHWARD SHIFT AND ARE NOW ON THE RIGHT SIDE OF THE MODEL GUIDANCE ENVELOPE. THE CANADIAN AND ECMWF MODELS HAVE ALSO SHIFTED NORTHWARD AND NO LONGER TAKE CHRIS ACROSS THE GREATER ANTILLES. THE LONE OUTLIER MODEL APPEARS TO BE THE GFDL...WHICH ALMOST IMMEDIATELY TAKES CHRIS DUE WEST ACROSS THE NORTH COAST OF PUERTO RICO AND INTO HISPANIOLA. THE OFFICIAL FORECAST TRACK IS A LITTLE NORTH OF THE PREVIOUS TRACK...AND MUCH FARTHER NORTH THAN THE MODEL CONSENSUS DUE TO THE GFDL MODEL BEING A LARGE OUTLIER. IT SHOULD BE POINTED OUT THAT THE GFS...GFS ENSEMBLE...UKMET...AND NOGAPS CONSENSUS FORECAST PLACES CHRIS VERY NEAR THE SOUTHERN TIP OF FLORIDA IN 120 HOURS...AND SUBSEQUENT FORECAST TRACKS MAY HAVE TO SHIFTED A LITTLE FARTHER NORTH IF THOSE MODEL TRENDS CONTINUE. THE INTENSITY FORECAST REMAINS PROBLEMATIC. THE GFS-BASED SHIPS INTENSITY MODEL INDICATES THE VERTICAL SHEAR IS EXPECTED TO WEAKEN TO LESS THAN 5-10 KT BY 96 AND 120 HOURS...YET SHOWS LITTLE INTENSIFICATION AND BARELY MAKES CHRIS A HURRICANE...EVEN THOUGH THE CYCLONE WILL BE OVER 29.5C TO 30C SSTS AND BETWEEN TWO UPPER-LEVEL LOWS THAT WILL ENHANCE THE OUTFLOW TO THE WEST AND EAST. GIVEN THAT CHRIS IS A SMALL TROPICAL CYCLONE...WHICH MEANS IT CAN SPIN UP QUICKLY BUT ALSO SPIN DOWN JUST AS QUICKLY...THE INTENSITY FORECAST WILL REMAIN ON THE CONSERVATIVE SIDE AT THIS TIME IN HE LONGER TIME PERIODS...BUT STILL ABOVE THE SHIPS MODEL. TROPICAL STORM WARNINGS REMAIN IN EFFECT FOR PUERTO RICO AND THE VIRGIN ISLANDS DUE TO THE POSSIBILITY OF A STRONG RAIN BAND DEVELOPING ON THE SOUTH SIDE OF CHRIS AND MOVING OVER THOSE AREAS LATER TODAY OR TONIGHT. FORECAST POSITIONS AND MAX WINDS INITIAL 02/0900Z 18.8N 62.6W 50 KT 12HR VT 02/1800Z 19.4N 64.0W 55 KT 24HR VT 03/0600Z 20.0N 65.8W 60 KT 36HR VT 03/1800Z 20.6N 67.6W 65 KT 48HR VT 04/0600Z 21.2N 69.5W 65 KT 72HR VT 05/0600Z 22.2N 73.5W 65 KT 96HR VT 06/0600Z 23.3N 77.5W 70 KT 120HR VT 07/0600Z 24.5N 82.5W 70 KT |
