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Chill falls over the Atlantic as the official season heads towards close
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| #210428 (Received by flhurricane at: 10:58 AM 25.Aug.2008) TCDAT2 TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072008 1100 AM EDT MON AUG 25 2008 VISIBLE SATELLITE IMAGES SHOW A SIGNIFICANT INCREASE IN ORGANIZATION OF THE LOW PRESSURE SYSTEM THAT WE HAVE BEEN MONITORING IN THE CARIBBEAN. WELL-DEFINED CURVED BAND FEATURES HAVE DEVELOPED... PARTICULARLY OVER THE NORTHERN AND WESTERN PORTIONS OF THE SYSTEM. ANALYSIS OF DIRECTIONAL AMBIGUITIES FROM A QUIKSCAT OVERPASS INDICATED A SURFACE CIRCULATION CENTER. THEREFORE WE ARE INITIATING ADVISORIES ON TROPICAL DEPRESSION SEVEN. AN SSM/IS IMAGE FROM SEVERAL HOURS AGO DEPICTED AN EYE-LIKE FEATURE AT THE 91 GHZ FREQUENCY...BUT IT WAS NOT EVIDENT ON THE 37 GHZ CHANNEL. SINCE THE LATTER CHANNEL IS MORE SENSITIVE TO THE LOWER-LEVELS... THIS EYE-LIKE FEATURE WAS PRIMARILY ALOFT. INTERESTINGLY HOWEVER...THE GEOSTATIONARY IMAGES ALSO SHOW A RELATIVELY CLEAR AREA NEAR THE CENTER THAT RESEMBLES AN EYE. OUR INITIAL INTENSITY ESTIMATE IS CONSERVATIVELY SET AT 30 KT BASED ON AN EARLIER REPORT FROM NOAA DATA BUOY 42059. OBSERVATIONS FROM AN UPCOMING AIR FORCE HURRICANE HUNTER MISSION SHOULD GIVE UPDATED INFORMATION ON THE STRENGTH OF THE SYSTEM. UPPER-LEVEL OUTFLOW IS WELL-DEFINED OVER ALL BUT THE SOUTHEAST QUADRANT. ATMOSPHERIC AND OCEANIC CONDITIONS APPEAR FAVORABLE FOR INTENSIFICATION AND THE OFFICIAL FORECAST IS CLOSE TO THE LATEST SHIPS GUIDANCE. CURIOUSLY...THE GFS HAS FAILED TO PREDICT DEVELOPMENT OF THE CYCLONE THUS FAR. INITIAL MOTION IS ABOUT 305/13 ALTHOUGH RECENT IMAGES SUGGEST THAT THE MOTION MAY BE A BIT TO THE LEFT OF THIS VALUE. THERE IS AN UNUSUALLY LARGE SPREAD TO OUR TRACK MODEL GUIDANCE THAT SEEMS TO BE THE RESULT OF TWO PRIMARY SCENARIOS FOR THE FUTURE MOTION OF THE SYSTEM. ONE WOULD BE A GENERALLY NORTHWARD TRACK INTO A WEAKNESS IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC...AND THIS IS DEPICTED BY THE NOGAPS AND ECMWF SOLUTIONS. A SECOND SCENARIO IS FOR THE TROPICAL CYCLONE TO BEND MORE WESTWARD IN RESPONSE TO A MID-LEVEL ANTICYCLONE OVER FLORIDA...AND THAT IS DEPICTED BY THE BAM TRACKS...THE HWRF...AND THE GFDL. OUR FIRST OFFICIAL TRACK FORECAST SOMEWHAT SPLITS THE DIFFERENCE BUT LEANS TOWARD THE LATTER SCENARIO. HOWEVER IT SHOULD BE NOTED THAT THE CONFIDENCE IN THIS TRACK FORECAST IS NOT HIGH...PARTICULARLY AT DAYS 4 AND 5. THIS FORECAST TRACK REQUIRES THE ISSUANCE OF TROPICAL STORM WARNINGS AND WATCHES FOR PORTIONS OF HISPANIOLA AT THIS TIME. FORECAST POSITIONS AND MAX WINDS INITIAL 25/1500Z 15.5N 70.1W 30 KT 12HR VT 26/0000Z 16.5N 71.1W 40 KT 24HR VT 26/1200Z 17.6N 72.2W 50 KT 36HR VT 27/0000Z 18.8N 73.3W 50 KT 48HR VT 27/1200Z 19.7N 74.2W 55 KT 72HR VT 28/1200Z 21.0N 75.5W 55 KT 96HR VT 29/1200Z 22.0N 77.0W 60 KT 120HR VT 30/1200Z 22.5N 78.0W 60 KT $$ FORECASTER PASCH/ROBERTS |
