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 721 
 WTNT42 KNHC 290850
 TCDAT2
  
 TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
 500 AM AST MON AUG 29 2011
  
 THE AREA OF LOW PRESSURE IN THE FAR EASTERN ATLANTIC TO THE SOUTH OF
 THE CAPE VERDE ISLANDS HAS GAINED SUFFICIENT CONVECTIVE
 ORGANIZATION TO BE CLASSIFIED AS A TROPICAL DEPRESSION. A CURVED
 CONVECTIVE BAND WRAPS AROUND THE WESTERN AND SOUTHERN SIDE OF THE
 SYSTEM AND THE INITIAL INTENSITY IS SET TO 30 KT BASED ON THE 06Z
 DVORAK CLASSIFICATION FROM TAFB. THE DEPRESSION IS CURRENTLY IN AN
 EASTERLY SHEAR ENVIRONMENT SITUATED TO THE SOUTH OF AN UPPER-LEVEL
 RIDGE OVER THE EASTERN ATLANTIC. SOME EASTERLY SHEAR IS EXPECTED TO
 PERSIST...BUT OTHERWISE THE ENVIRONMENT SHOULD BE CONDUCIVE FOR
 STRENGTHENING THROUGH THE PERIOD. THE OFFICIAL INTENSITY FORECAST
 SHOWS SLOW STRENGTHENING IN GOOD AGREEMENT WITH THE SHIPS...GFDL...
 AND HWRF MODELS THROUGH 48 HOURS. AFTER THAT TIME THE CYCLONE SHOULD
 STRENGTHEN A LITTLE MORE QUICKLY AS IT MOVES OVER PROGRESSIVELY
 HIGHER OCEAN HEAT CONTENT. AT DAYS 3 THROUGH 5 THE NHC FORECAST IS
 CLOSEST TO BUT A LITTLE BELOW THE HWRF MODEL. THE SHIPS FORECAST
 LATE IN THE PERIOD APPEARS TOO LOW DUE TO STRONG SOUTHERLY SHEAR
 IMPARTED BY THE TROPICAL CYCLONE VORTEX IN THE GFS MODEL FIELDS...
 WHICH IS DISPLACED TO THE SOUTH AND EAST OF THE OFFICIAL TRACK.
  
 THE INITIAL MOTION ESTIMATE IS TOWARD THE WEST OR 270 DEGREES AT 13
 KNOTS. THE DEPRESSION IS CURRENTLY SITUATED TO THE SOUTH OF THE
 SUBTROPICAL RIDGE...BUT THE WESTERN EDGE OF THE RIDGE WILL WEAKEN
 OVER THE NEXT DAY OR TWO AS A MID/UPPER-LEVEL LOW CUTS OFF AND
 RETROGRADES ACROSS THE CENTRAL ATLANTIC. THIS WILL ALLOW THE
 DEPRESSION TO TURN TOWARD THE WEST-NORTHWEST DURING THE NEXT DAY OR
 SO. AFTER 48 HOURS...THE MID/UPPER-LEVEL-LOW WEAKENS AND THE RIDGE
 RE-STRENGTHENS TO THE NORTHEAST OF THE CYCLONE...WHICH SHOULD
 RESULT IN A CONTINUED WEST-NORTHWESTWARD MOTION THROUGH THE END OF
 THE PERIOD. THE OFFICIAL NHC TRACK FORECAST IS SOUTH OF AND FASTER
 THAN MOST OF THE GUIDANCE FOR THE FIRST 48 HOURS...AS MOST OF THE
 DYNAMICAL MODELS SHOW A MORE POLEWARD AND SLOWER MOTION THAN IS
 CURRENTLY OBSERVED. DURING THIS TIME THE NHC TRACK IS BETWEEN THE
 DYNAMICAL MODEL CONSENSUS AND THE LBAR...WHICH TYPICALLY PERFORMS
 WELL IN THE DEEP TROPICS. AT 72 HOURS AND BEYOND THE NHC FORECAST
 IS CLOSE TO A BLEND OF THE HWRF...GFDL...AND ECMWF MODELS AND IS
 MUCH FASTER THAN THE LATEST RUN OF THE GFS.
   
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  29/0900Z  9.4N  26.3W   30 KT  35 MPH
  12H  29/1800Z  9.8N  28.3W   35 KT  40 MPH
  24H  30/0600Z 10.7N  30.9W   40 KT  45 MPH
  36H  30/1800Z 11.9N  33.5W   45 KT  50 MPH
  48H  31/0600Z 13.1N  36.3W   50 KT  60 MPH
  72H  01/0600Z 15.0N  42.5W   65 KT  75 MPH
  96H  02/0600Z 16.5N  48.0W   75 KT  85 MPH
 120H  03/0600Z 18.0N  52.0W   85 KT 100 MPH
  
 $$
 FORECASTER BRENNAN
  
 
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