Tropical Depression 7: Forecast Discussion #1

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


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