WTNT43 KNHC 252034
TCDAT3
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082009
500 PM AST FRI SEP 25 2009
 
SATELLITE IMAGERY INDICATES THAT THE TROPICAL WAVE OVER THE EASTERN
ATLANTIC HAS DEVELOPED SUFFICIENT CONVECTION AND CIRCULATION TO BE
DESIGNATED A TROPICAL DEPRESSION.   SATELLITE INTENSITY ESTIMATES
BASED ON BANDING IN THE NORTHERN SEMICIRCLE ARE 30 KT FROM TAFB AND
25 KT FROM SAB.  THE INITIAL INTENSITY IS SET TO 30 KT.  THE CIRRUS
OUTFLOW IS FAIR TO GOOD IN THE NORTHERN SEMICIRCLE AND RESTRICTED
ELSEWHERE.
 
THE DEPRESSION IS CURRENTLY EXPERIENCING 10-15 KT OF SOUTHWESTERLY
VERTICAL WIND SHEAR.  THE SHEAR IS FORECAST TO INCREASE AFTER 12 HR
OR SO...WITH THE FORECAST TRACK LIKELY TAKING THE CYCLONE NEAR AN
UPPER-LEVEL TROUGH BY 48 HR.  THIS...COMBINED WITH A TONGUE OF
COOLER SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK...SUGGEST
THAT THE SYSTEM WILL ONLY HAVE A SMALL CHANCE TO STRENGTHEN BEFORE
ENCOUNTERING CONDITIONS THAT SHOULD CAUSE DISSIPATION.  THE
INTENSITY FORECAST CALLS FOR SLIGHT STRENGTHENING DURING THE FIRST
12 HR...FOLLOWED BY GRADUAL WEAKENING.  THE SYSTEM IS FORECAST TO
BECOME A REMNANT LOW BY 72 HR AND DISSIPATE COMPLETELY BY 96 HR.
 
THE INITIAL MOTION IS 305/12.  THE CYCLONE IS FORECAST TO CONTINUE
THIS GENERAL MOTION TOWARD AN UPPER-LEVEL TROUGH AND AN ASSOCIATED
WEAKNESS IN THE LOW/MID-LEVEL SUBTROPICAL RIDGE FOR THE NEXT 36 HR
OR SO...THEN TURN NORTHWARD INTO THE WEAKNESS BEFORE DISSIPATION.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/2100Z 16.4N  31.6W    30 KT
 12HR VT     26/0600Z 17.3N  33.1W    35 KT
 24HR VT     26/1800Z 18.4N  35.0W    35 KT
 36HR VT     27/0600Z 19.8N  36.8W    30 KT
 48HR VT     27/1800Z 21.4N  38.1W    25 KT
 72HR VT     28/1800Z 24.0N  39.5W    20 KT...REMNANT LOW
 96HR VT     29/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT43 KNHC 260236
TCDAT3
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082009
1100 PM AST FRI SEP 25 2009
 
THE CLOUD PATTERN HAS NOT BECOME ANY BETTER ORGANIZED DURING THE
PAST SEVERAL HOURS. THE CONVECTION WAS MINIMAL BUT IT HAS BEGUN TO
BLOSSOM AS WE SPEAK. ALTHOUGH THE T-NUMBERS HAVE DECREASED...FOR
THE SAKE OF CONTINUITY...THE INITIAL INTENSITY IS KEPT AT 30 KNOTS.
THE ENVIRONMENT IS EXPECTED TO BE MARGINAL FOR STRENGTHENING DURING
THE NEXT 12 HOURS OR SO...AND THE DEPRESSION HAS A SMALL
OPPORTUNITY TO BECOME A TROPICAL STORM ON SATURDAY. THEREAFTER...
STRONG SHEAR AND COOLER WATERS WILL INDUCE WEAKENING...AND THE
CYCLONE IS EXPECTED TO BECOME A REMNANT LOW BY 72 HOURS OR SOONER. 

THE DEPRESSION IS MOVING TOWARD THE NORTHWEST OR 310 DEGREES AT 10
KNOTS WHILE LOCATED ON THE SOUTHWEST SIDE OF A SMALL MID-LEVEL
RIDGE OF HIGH PRESSURE.  SINCE THE PATTERN IS NOT EXPECTED TO
CHANGE...THIS GENERAL MOTION IS FORECAST TO CONTINUE UNTIL
DISSIPATION. MOST OF THE GLOBAL MODELS DO NOT EVEN ACKNOWLEDGE THE
PRESENCE OF THE DEPRESSION OR DEPICT THE DEPRESSION AS A SMALL
VORTMAX. 
 
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0300Z 17.4N  32.3W    30 KT
 12HR VT     26/1200Z 18.4N  33.9W    35 KT
 24HR VT     27/0000Z 19.6N  36.0W    30 KT
 36HR VT     27/1200Z 21.0N  37.5W    25 KT
 48HR VT     28/0000Z 22.5N  38.8W    25 KT
 72HR VT     29/0000Z 24.0N  40.0W    20 KT...REMNANT LOW
 96HR VT     30/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

WTNT43 KNHC 260848
TCDAT3
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082009
500 AM AST SAT SEP 26 2009
 
WHILE DEEP CONVECTION HAS INCREASED OVER THE PAST FEW HOURS...
GEOSTATIONARY IMAGERY AND AN AMSR-E PASS FROM AROUND 0400 UTC
SUGGEST THAT THE LOW-LEVEL CENTER IS LOCATED ON THE SOUTHWESTERN
EDGE OF THE CONVECTION. THIS STRUCTURE IS LIKELY DUE TO THE 10-15
KT OF SOUTHWESTERLY SHEAR ANALYZED OVER THE CYCLONE BY UW-CIMSS AND
THE SHIPS MODEL. DVORAK CI-NUMBERS WERE 1.5 AND 2.0 FROM SAB AND
TAFB...RESPECTIVELY...AND THE INITIAL INTENSITY IS HELD AT 30 KT
FOR THIS ADVISORY. CONDITIONS WILL BE ONLY MARGINALLY FAVORABLE FOR
INTENSIFICATION OVER THE NEXT 2-3 DAYS. SSTS WILL BE 26-27C...AND
THE SHIPS MODEL SHOWS THE SHEAR DECREASING BELOW 15 KT ONLY FOR A
BRIEF PERIOD FROM 12 TO 24 HOURS. GIVEN THIS...THE OFFICIAL
FORECAST HOLDS THE INTENSITY AT 30 KT THROUGH 24 HOURS AND THEN
SHOWS A GRADUAL WEAKENING. HOWEVER...IT IS POSSIBLE THAT THE SYSTEM
COULD BRIEFLY REACH TROPICAL STORM STATUS DURING THE NEXT DAY OR
SO. 
 
THE INITIAL MOTION ESTIMATE IS 300/12...A LITTLE TO THE LEFT OF THE
PREVIOUS ADVISORY. MOST OF THE TRACK GUIDANCE INDICATES THAT THE
CYCLONE WILL ROUND THE WESTERN EDGE OF THE SUBTROPICAL RIDGE AND
TURN TOWARD THE NORTHWEST OVER THE NEXT COUPLE OF DAYS. BEYOND THAT
TIME...THE GFS...NOGAPS AND HWRF SHOW THE DEPRESSION OR ITS REMNANTS
TURNING NORTHWARD AHEAD OF A FRONT...WHILE THE UKMET...ECMWF...AND
THE MEDIUM BAM SUGGEST THAT WHAT IS LEFT OF THE CYCLONE WILL TURN
WESTWARD. THE OFFICIAL FORECAST IS SOUTH OF THE PREVIOUS ONE FOR
THE FIRST 24 HOURS DUE TO THE INITIAL MOTION...AND IS AN UPDATE OF
THE PREVIOUS FORECAST BEYOND THAT TIME. AT DAY 3 ONLY A SLOW
NORTHWESTWARD MOTION IS INDICATED DUE TO THE LARGE SPREAD IN THE
GUIDANCE.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0900Z 17.6N  33.8W    30 KT
 12HR VT     26/1800Z 18.7N  35.3W    30 KT
 24HR VT     27/0600Z 20.2N  36.9W    30 KT
 36HR VT     27/1800Z 21.6N  38.1W    25 KT
 48HR VT     28/0600Z 23.1N  39.3W    25 KT
 72HR VT     29/0600Z 24.5N  40.5W    20 KT...REMNANT LOW
 96HR VT     30/0600Z...DISSIPATED
 
$$
FORECASTER BRENNAN
 

WTNT43 KNHC 261431
TCDAT3
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082009
1100 AM AST SAT SEP 26 2009

SATELLITE IMAGERY THIS MORNING INDICATES THAT TROPICAL DEPRESSION
EIGHT HAS BECOME A LITTLE LESS ORGANIZED...WHICH IS LIKELY TO DUE
TO 20 KT OF WEST-SOUTHWESTERLY VERTICAL WIND SHEAR INDICATED BY
ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN.  THE
CIRCULATION HAS BECOME ELONGATED ALONG A NORTHEAST-SOUTHWEST
AXIS...WITH TWO OR THREE EMBEDDED VORTICITY CENTERS NOTED.  IN
ADDITION...THE CONVECTIVE BANDING IS FARTHER FROM THE CENTER THAN
24 HR AGO. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB REMAIN
30 AND 25 KT...SO THE INITIAL INTENSITY REMAINS 30 KT.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/12.  THE LARGE-SCALE
MODELS FORECAST A LARGE-DEEP LAYER TROUGH AND ASSOCIATED SURFACE
COLD FRONT CURRENTLY OVER THE WESTERN ATLANTIC TO MOVE EASTWARD
DURING THE NEXT 48-96 HR.  THIS SHOULD CAUSE THE SUBTROPICAL RIDGE
OVER THE EASTERN ATLANTIC TO WEAKEN...AND SHOULD ALLOW THE TROPICAL
DEPRESSION TO TURN NORTHWARD AND THEN RECURVE INTO THE WESTERLIES
ON THE SOUTH SIDE OF THE TROUGH.  MOST OF THE TRACK GUIDANCE CALLS
FOR THIS SCENARIO...AND THE NEW TRACK FORECAST IS FOR RECURVATURE
AFTER 72 HR.  AN ALTERNATE SCENARIO IS SHOWN BY THE ECMWF...WHICH
FORECASTS THE DEPRESSION TO WEAKEN WITH THE REMNANT TROUGH MOVING
WESTWARD IN THE LOW-LEVEL FLOW.

THE INTENSITY FORECAST IS A LITTLE PROBLEMATIC.  THE DEPRESSION IS
NOT ONLY ENCOUNTERING MODERATE SHEAR...BUT IS ALSO OVER A TONGUE OF
COLDER SEA SURFACE TEMPERATURES AND HAS AN AREA OF DRY AIR JUST TO
ITS WEST.  WHILE THE SHEAR IS FORECAST TO CHANGE LITTLE DURING THE
NEXT 48-60 HR...THE SSTS INCREASE ALONG THE FORECAST TRACK.  THE
MOST LIKELY SCENARIO IS THAT THE COMBINATION OF SHEAR AND DRY AIR
WILL CAUSE THE DEPRESSION TO GRADUALLY DECAY OVER THE NEXT
48-72 HR.  ON THE OTHER HAND...WITH THE INCREASING SSTS...THE
CYCLONE COULD STRENGTHEN IF AND WHEN THE SHEAR DECREASES...AS
SUGGESTED AFTER 72 HR BY THE SHIPS...LGEM...AND GFDL MODELS.  THE
NEW INTENSITY FORECAST GOES WITH THE WEAKENING SCENARIO...CALLING
FOR THE DEPRESSION TO DECAY INTO A REMNANT LOW IN ABOUT 72 HR. 
HOWEVER... THERE IS LOWER CONFIDENCE IN THIS SCENARIO THAN THERE
WAS YESTERDAY.
 
THE DYNAMICAL MODELS SHOW THE DEPRESSION OR ITS REMNANTS SURVIVING
LONGER THAN THEY DID 24 HR AGO...SO A 96 HR FORECAST POINT HAS BEEN
ADDED.  THE SYSTEM IS EXPECTED TO DISSIPATE OR BE ABSORBED INTO THE
BAROCLINIC TROUGH BY 120 HR.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/1500Z 18.0N  34.8W    30 KT
 12HR VT     27/0000Z 19.1N  36.4W    30 KT
 24HR VT     27/1200Z 20.5N  37.8W    30 KT
 36HR VT     28/0000Z 21.9N  38.9W    25 KT
 48HR VT     28/1200Z 23.0N  40.0W    25 KT
 72HR VT     29/1200Z 24.5N  40.5W    20 KT...REMNANT LOW
 96HR VT     30/1200Z 26.0N  37.0W    20 KT...REMNANT LOW
120HR VT     01/1200Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT43 KNHC 262031
TCDAT3
TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082009
500 PM AST SAT SEP 26 2009

SATELLITE IMAGERY THIS AFTERNOON SHOWS THAT THE CIRCULATION OF
TROPICAL DEPRESSION EIGHT HAS WEAKENED TO AN ELONGATED TROUGH WITH
SEVERAL EMBEDDED VORTICITY CENTERS.  WHILE THE SYSTEM CONTINUES TO
PRODUCE CONVECTION THAT IS CLASSIFIABLE USING THE DVORAK
TECHNIQUE...IT NO LONGER HAS A WELL-ENOUGH DEFINED CIRCULATION TO
BE CONSIDERED A TROPICAL DEPRESSION.  THE REMNANT TROUGH OR
TROPICAL WAVE IS EXPECTED TO CONTINUE MOVING NORTHWESTWARD FOR THE
NEXT COUPLE OF DAYS.

THIS IS THE LAST ADVISORY ISSUED ON THIS SYSTEM BY THE NATIONAL
HURRICANE CENTER UNLESS REGENERATION OCCUR.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 18.9N  35.7W    25 KT
 12HR VT     27/0600Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

