WTNT42 KNHC 121455
TCDAT2
TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
1100 AM AST SUN SEP 12 2010
 
THE AREA OF LOW PRESSURE ASSOCIATED WITH A STRONG TROPICAL WAVE THAT
MOVED OFF THE WEST COAST OF AFRICA YESTERDAY NOW HAS ENOUGH
CONVECTIVE ORGANIZATION TO BE DECLARED A TROPICAL DEPRESSION.  THE
INITIAL INTENSITY IS SET AT 30 KT BASED ON A BLEND OF DVORAK
T-NUMBERS OF 2.5 AND 1.5 FROM TAFB AND SAB...RESPECTIVELY.
THE DEPRESSION HAS A LARGE CURVED BAND IN THE WESTERN SEMICIRCLE
...AND OUTFLOW IS GOOD IN THAT PORTION OF THE CIRCULATION.
 
ANALYSES FROM UW-CIMSS AND THE SHIPS MODEL SHOW ABOUT 10 KT OF
EASTERLY SHEAR OVER THE CYCLONE...HOWEVER THE SHEAR IS EXPECTED TO
DIMINISH IN THE NEXT 12 TO 24 HOURS. THE DEPRESSION WILL BE MOVING
OVER WARM WATERS FOR THE NEXT COUPLE OF DAYS...AND STEADY
INTENSIFICATION IS FORECAST.  BEYOND THAT TIME...THE CYCLONE WILL
BE MOVING OVER MARGINAL SEA SURFACE TEMPERATURES...AND THE SHIPS
MODEL SHOWS THE SHEAR INCREASING. THE STATISTICAL MODELS SHOW SOME
WEAKENING AT DAYS 4 AND 5...BUT THE DYNAMICAL MODELS SHOW THEIR
PEAK INTENSITY OF THE CYCLONE LATE IN THE PERIOD. AS A COMPROMISE
...THE OFFICIAL FORECAST SHOWS LITTLE CHANGE IN INTENSITY BEYOND 48
HOURS. THE NHC FORECAST IS IN BEST AGREEMENT WITH THE LGEM THROUGH
DAY 3 AND CLOSE TO ICON AT DAYS 4 AND 5.
 
THE INITIAL MOTION ESTIMATE IS 275/12...AS THE DEPRESSION IS
CURRENTLY LOCATED ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL
RIDGE THAT EXTENDS FROM NORTH AFRICA TO THE EASTERN ATLANTIC.  THE
CYCLONE WILL TURN WEST-NORTHWESTWARD AND NORTHWESTWARD AND SLOW DOWN
A LITTLE BY 48 HOURS AS IT APPROACHES A BREAK IN THE RIDGE TO THE
SOUTHWEST OF A MID- AND UPPER-LEVEL LOW EAST OF THE AZORES. ON DAYS
4 AND 5 THE MID- TO UPPER-LEVEL LOW MOVES EASTWARD.  THIS ALLOWS A
MID-LEVEL RIDGE TO BUILD IN EAST AND NORTH OF THE CYCLONE...WHICH
SHOULD RESULT IN AN ACCELERATION TOWARD THE NORTHWEST OR WEST-
NORTHWEST BY THE END OF THE PERIOD.  THE OFFICIAL FORECAST IS CLOSE
TO A BLEND OF ALL THE DYNAMICAL MODELS...WITH THE EXCEPTION OF THE
NOGAPS...WHICH APPEARS TO BE A SOUTHERLY OUTLIER.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/1500Z 12.7N  21.4W    30 KT
 12HR VT     13/0000Z 12.8N  23.3W    35 KT
 24HR VT     13/1200Z 13.5N  25.5W    45 KT
 36HR VT     14/0000Z 14.5N  27.7W    55 KT
 48HR VT     14/1200Z 15.7N  29.4W    65 KT
 72HR VT     15/1200Z 19.0N  32.5W    65 KT
 96HR VT     16/1200Z 23.0N  37.0W    65 KT
120HR VT     17/1200Z 26.5N  43.0W    65 KT
 
$$
FORECASTER BRENNAN
 

WTNT42 KNHC 122046
TCDAT2
TROPICAL DEPRESSION TWELVE DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL122010
500 PM AST SUN SEP 12 2010
 
RECENT SATELLITE IMAGERY SHOWS AN INCREASE IN DEEP CONVECTION JUST
TO THE WEST OF THE ESTIMATED CENTER POSITION...HOWEVER THE INTENSITY
IS BEING HELD AT 30 KT FOR THIS ADVISORY BASED ON A BLEND OF DVORAK
ESTIMATES FROM TAFB AND SAB.  THE DEPRESSION IS STILL EXPERIENCING
SOME EASTERLY SHEAR...HOWEVER THE SHIPS MODEL FORECASTS THE SHEAR
TO WEAKEN IN THE NEXT 12 HOURS AND STAY BELOW 15 KT UNTIL 72 HOURS.
THE INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY...
SHOWING STEADY STRENGTHENING THROUGH 48 HOURS IN BEST AGREEMENT WITH
THE SHIPS MODEL. AFTER THAT TIME...SEA SURFACE TEMPERATURES COOL
ALONG THE TRACK AND THE SHEAR INCREASES AS THE CYCLONE INTERACTS
WITH AN UPPER-LEVEL TROUGH/LOW AS INDICATED BY SEVERAL OF THE
GLOBAL MODELS.  GIVEN THE MIXED TRENDS IN THE GUIDANCE AT THIS TIME
PERIOD...THE OFFICIAL FORECAST WILL HOLD THE INTENSITY AT 65 KT
THROUGH DAY 5. 
 
THE CURRENT POSITION IS A LITTLE NORTH OF THE PREVIOUS TRACK...AND
THE INITIAL MOTION ESTIMATE IS 280 DEGREES AT 12 KT. THE OVERALL
THE SYNOPTIC REASONING REMAINS UNCHANGED.  A WEST-NORTHWESTWARD
TURN IS EXPECTED SOON AS THE DEPRESSION MOVES AROUND THE WESTERN
PERIPHERY OF THE SUBTROPICAL RIDGE OVER THE EASTERN ATLANTIC. THIS
MOTION IS EXPECTED CONTINUE THROUGH 36 TO 48 HOURS WHEN THE
DEPRESSION WILL TURN NORTHWESTWARD INTO A BREAK IN THE RIDGE. AT
DAYS 4 AND 5 A TURN BACK TOWARD THE WEST-NORTHWEST IS EXPECTED WITH
AN INCREASE IN FORWARD SPEED AS CYCLONE MOVES AROUND THE EASTERN
SIDE OF A UPPER-LEVEL LOW THAT CUTS OFF NEAR 40W. THE OFFICIAL NHC
FORECAST IS NORTH OF THE PREVIOUS ONE THROUGH 36 HOURS DUE TO THE
INITIAL POSITION AND MOTION...AND BEYOND THAT TIME IS BASICALLY AN
EXTENSION OF THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      12/2100Z 13.3N  22.8W    30 KT
 12HR VT     13/0600Z 13.7N  24.6W    35 KT
 24HR VT     13/1800Z 14.6N  27.1W    45 KT
 36HR VT     14/0600Z 15.6N  29.0W    55 KT
 48HR VT     14/1800Z 16.9N  30.6W    65 KT
 72HR VT     15/1800Z 20.4N  34.2W    65 KT
 96HR VT     16/1800Z 24.0N  39.5W    65 KT
120HR VT     17/1800Z 27.1N  45.5W    65 KT
 
$$
FORECASTER BRENNAN
 

