WTNT41 KNHC 281450
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
1100 AM EDT THU MAY 28 2009
 
DEEP CONVECTION ASSOCICATED WITH THE AREA OF LOW PRESSURE OFF THE
MID-ATLANTIC COAST HAS BEEN PERSISTENT SINCE ABOUT 04Z THIS MORNING
WHILE THE SYSTEM MOVES OVER THE 25-26C WATERS OF THE GULF
STREAM.  DVORAK CLASSIFICATIONS FROM TAFB AND SAB AT 12Z WERE
T2.0 AND T1.5...RESPECTIVELY.  AN AMSU PASS AT 1033Z HELPS TO PLACE
THE CENTER ON THE NORTHWEST EDGE OF THE DEEP CONVECTION.  BASED ON
THESE DATA...THE SYSTEM IS BEING UPGRADED TO A TROPICAL
DEPRESSION...THE FIRST OF THE ATLANTIC HURRICANE SEASON.
 
THE INITIAL MOTION IS 050/15.  THE DEPRESSION IS EMBEDDED IN A
SOUTHWESTERLY STEERING CURRENT AHEAD OF A DEEP-LAYER TROUGH OVER
THE CENTRAL UNITED STATES.  THIS BASIC PATTERN IS EXPECTED TO
PERSIST...AND THE DYNAMICAL MODEL GUIDANCE IS IN PRETTY GOOD
AGREEMENT...AT LEAST THROUGH 36 HOURS...WHEN THE SYSTEM BEGINS TO
LOSE DEFINITION IN MUCH OF THE GUIDANCE.
 
VERTICAL SHEAR OVER THE SYSTEM IS LIGHT...AND THE CYCLONE IS LIVING
OFF THE NARROW GULF STREAM WATERS.  AS LONG AS IT REMAINS THERE SOME
STRENGTHENING IS POSSIBLE.  ALTHOUGH THE SHIPS GUIDANCE DOES NOT
SHOW THE SYSTEM REACHING TROPICAL STORM STRENGTH...THE INITIAL SST
INPUT TO THE MODEL APPEAR TOO COLD.  AS A RESULT...THE OFFICIAL
FORECAST WILL CALL FOR THE SYSTEM TO BECOME A TROPICAL STORM OVER
THE NEXT DAY OR SO.  AFTER THAT...A LOSS OF CONVECTION...AND
TROPICAL CHARACTERISTICS...IS EXPECTED.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/1500Z 37.3N  71.0W    30 KT
 12HR VT     29/0000Z 38.5N  68.4W    35 KT
 24HR VT     29/1200Z 40.2N  64.6W    35 KT
 36HR VT     30/0000Z 41.5N  60.0W    30 KT
 48HR VT     30/1200Z 43.0N  55.0W    25 KT...EXTRATROPICAL
 72HR VT     31/1200Z 46.0N  46.0W    25 KT...EXTRATROPICAL
 96HR VT     01/1200Z...DISSIPATED
 
$$
FORECASTER FRANKLIN/BEVEN
 

WTNT41 KNHC 282031
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
500 PM AST THU MAY 28 2009
 
CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION ONE HAS DECREASED
SOMEWHAT THIS AFTERNOON AND IS NOW LIMITED TO THE SOUTHEASTERN
QUADRANT.  SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE
30 KT...WHICH REMAINS THE INITIAL INTENSITY.  THE FORECAST TRACK
KEEPS THE CENTER OVER THE GULF STREAM FOR THE NEXT 6-12 HR IN A
LIGHT SHEAR ENVIRONMENT...SO SOME SLIGHT STRENGTHENING COULD OCCUR
DURING THAT TIME AS SHOWN BY THE SHIPS MODEL.  AFTER THAT...COLDER
SEA SURFACE TEMPERATURES AND INCREASING SHEAR SHOULD CAUSE
WEAKENING.  THE CYCLONE IS EXPECTED TO BECOME EXTRATROPICAL BY
36 HR AND DISSIPATE COMPLETELY AFTER 48 HR.  IT IS POSSBLE THAT BOTH
OF THESE EVENTS COULD HAPPEN EARLIER THAN CURRENTLY FORECAST.
 
THE INITIAL MOTION IS 055/14.  THE DEPRESSION IS EMBEDDED IN THE
WESTERLIES BETWEEN THE SUBTROPICAL RIDGE TO THE SOUTHEAST AND A
DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES AND EASTERN
CANADA.  THIS PATTERN SHOULD STEER THE CYCLONE GENERALLY
EAST-NORTHEASTWARD UNTIL DISSIPATION.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      28/2100Z 37.7N  69.4W    30 KT
 12HR VT     29/0600Z 38.7N  67.0W    35 KT
 24HR VT     29/1800Z 40.4N  62.8W    30 KT
 36HR VT     30/0600Z 42.2N  57.5W    25 KT...EXTRATROPICAL
 48HR VT     30/1800Z 43.9N  52.5W    25 KT...EXTRATROPICAL
 72HR VT     31/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN
 

WTNT41 KNHC 290256
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
1100 PM AST THU MAY 28 2009
 
THE LAST FEW VISIBLE IMAGES INDICATED THAT THE LOW-LEVEL CENTER OF
THE DEPRESSION WAS BECOMING SOMEWHAT EXPOSED TO THE NORTHWEST OF
THE DEEP CONVECTION.  THE CONVECTION ITSELF HAS SHRUNK A BIT IN SIZE
OVER THE PAST FEW HOURS...AND DATA T-NUMBERS HAVE FALLEN TO 1.5
FROM SAB AND REMAIN 2.0 FROM TAFB.  A QUIKSCAT PASS AT 2330 UTC
SHOWED A FEW TROPICAL-STORM-FORCE VECTORS THAT APPEAR TO HAVE BEEN
AFFECTED BY RAIN.  THEREFORE...THE INITIAL INTENSITY IS BEING
HELD AT 30 KT. 

SEA SURFACE TEMPERATURE DATA SHOW THAT THE DEPRESSION IS CURRENTLY
HUGGING THE NORTH WALL OF THE GULF STREAM...AND THE FORECAST TRACK
TAKES THE CENTER NORTHWARD ACROSS THE WALL OVER COLDER WATERS
WITHIN THE NEXT 12 HOURS. THE OFFICIAL FORECAST STILL ALLOWS FOR
THE POSSIBILITY THAT THE DEPRESSION COULD BECOME A TROPICAL STORM
BEFORE THIS HAPPENS...BUT IT WILL HAVE TO HAPPEN SOON. THE GLOBAL
MODEL GUIDANCE GENERALLY INDICATES THAT THE DEPRESSION WILL BE
TANGLED WITHIN A BAROCLINIC ZONE TO ITS NORTH WITHIN THE NEXT 24
HOURS...SO THE OFFICIAL FORECAST CALLS FOR IT TO BE EXTRATROPICAL
AT THAT POINT. DISSIPATION IS EXPECTED BY 48 HOURS AS THE SYSTEM IS
OVERTAKEN BY ANOTHER LOW PRESSURE SYSTEM CURRENTLY NEAR NEW
ENGLAND.
 
THE DEPRESSION HAS BEEN MOVING A LITTLE SOUTH OF THE PREVIOUS TRACK
AND THE BULK OF THE MODELS.  THE INITIAL MOTION IS 070/13 AS THE
SYSTEM IS BEING STEERED BETWEEN THE SUBTROPICAL RIDGE AND A LARGE
TROUGH OVER EASTERN NORTH AMERICA.  THE OFFICIAL FORECAST IS ON THE
SOUTH SIDE OF THE GUIDANCE ENVELOPE.
 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/0300Z 38.1N  67.8W    30 KT
 12HR VT     29/1200Z 39.1N  65.0W    35 KT
 24HR VT     30/0000Z 41.2N  60.5W    30 KT...EXTRATROPICAL
 36HR VT     30/1200Z 43.4N  55.4W    30 KT...EXTRATROPICAL
 48HR VT     31/0000Z...DISSIPATED
 
$$
FORECASTER BERG
 

WTNT41 KNHC 290833
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
500 AM AST FRI MAY 29 2009
 
AFTER AN INCREASE IN DEEP CONVECTION THAT BEGAN AROUND 0400
UTC...SATELLITE IMAGERY INDICATES THAT THE CONVECTION HAS BEGUN TO
DECREASE AND MOVE EASTWARD AWAY FROM THE LOW LEVEL CIRCULATION
CENTER.  DVORAK T-NUMBERS AT 0600 UTC WERE 2.5 AND 1.5 FROM TAFB
AND SAB...RESPECTIVELY...AND THE CURRENT INTENSITY IS HELD AT 30 KT
BASED ON A BLEND OF THESE ESTIMATES.  THIS INTENSITY IS ALSO
SUPPORTED BY AN ASCAT PASS OVER THE SYSTEM AT 0102 UTC THAT SHOWED
MAXIMUM WINDS OF AROUND 30 KT.
 
THE CENTER OF THE DEPRESSION IS VERY CLOSE TO THE NORTHERN WALL OF
THE GULF STREAM...AND THE FORECAST TRACK TAKES THE CYCLONE OVER
COLDER WATER TODAY.  THEREFORE...IT APPEARS THAT THE OPPORTUNITY FOR
THIS SYSTEM TO REACH TROPICAL STORM STRENGTH HAS PASSED.  MOST OF
THE GLOBAL MODEL GUIDANCE SHOWS THE CYCLONE BECOMING EXTRATROPICAL
WITHIN 24 HOURS AS IT BECOMES ENTANGLED WITH A FRONTAL BOUNDARY TO
THE NORTH.  THESE MODELS ALSO SHOW THE CYCLONE DISSIPATING BY 36
HOURS...HOWEVER THIS COULD OCCUR SOONER IF THE CIRCULATION BECOMES
POORLY DEFINED AS IT INTERACTS WITH THE FRONT.
 
THE DEPRESSION APPEARS TO BE MOVING AROUND 070/13.  THE CYCLONE IS
BEING STEERED BY DEEP LAYER SOUTHWESTERLY FLOW BETWEEN THE
SUBTROPICAL RIDGE AND A TROUGH OVER EASTERN NORTH AMERICA.  MOST OF
THE MODEL GUIDANCE...WITH THE EXCEPTION OF THE GFS AND CANADIAN...
ARE TO THE LEFT OF THE PREVIOUS TRACK.  THE OFFICIAL FORECAST HAS
BEEN ADJUSTED TOWARD THIS MULTI-MODEL CONSENSUS.
  
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/0900Z 38.9N  66.3W    30 KT
 12HR VT     29/1800Z 40.2N  63.7W    30 KT
 24HR VT     30/0600Z 42.5N  59.1W    25 KT...EXTRATROPICAL
 36HR VT     30/1800Z...DISSIPATED
 
$$
FORECASTER BRENNAN/BROWN
 

WTNT41 KNHC 291433
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
1100 AM AST FRI MAY 29 2009
 
SATELLITE IMAGERY INDICATES THAT THE CLOUD PATTERN ASSOCIATED WITH
THE DEPRESSION HAS BECOME DISORGANIZED...WITH INCREASING WESTERLY
SHEAR DISPLACING THE REMAINING DEEP CONVECTION TO THE SOUTHEAST OF
THE CENTER.  SATELLITE CLASSIFICATIONS FROM TAFB AND SAB CONFIRM
THIS DEGRADATION IN APPEARANCE...BUT WINDS ARE CONSERVATIVELY KEPT
AT 30 KT THIS ADVISORY BASED ON EARLIER ASCAT ESTIMATES.

THE DEPRESSION IS EMBEDDED IN A DEEP-LAYER SOUTHWESTERLY FLOW AHEAD
OF A DEVELOPING TROUGH OVER EASTERN NORTH AMERICA...WITH AN
ESTIMATED INITIAL MOTION OF 065/16...SLIGHTLY FASTER THAN BEFORE.
SHORT-TERM MODEL GUIDANCE IS IN GOOD AGREEMENT AND SUGGESTS A
FURTHER ACCELERATION DURING THE NEXT 12 TO 24 HOURS.

THE DEPRESSION HAS REACHED COLDER WATERS...AND THE FORECAST TRACK
TAKES THE SYSTEM OVER EVEN COLDER WATERS LATER TODAY AND TONIGHT. 
IN ADDITION...THE DEPRESSION IS BEGINNING TO MERGE WITH A FRONTAL
SYSTEM DEVELOPING NEAR AND NORTHEAST OF THE CENTER.  THE MAJORITY
OF GLOBAL MODELS INDICATE EXTRATROPICAL TRANSITION WITHIN 12 HOURS
AND ABSORPTION BY THE FRONTAL ZONE SHORTLY THEREAFTER.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/1500Z 39.6N  64.0W    30 KT
 12HR VT     30/0000Z 41.2N  61.2W    25 KT...EXTRATROPICAL
 24HR VT     30/1200Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN/BEVEN
 

WTNT41 KNHC 292035
TCDAT1
TROPICAL DEPRESSION ONE DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL012009
500 PM AST FRI MAY 29 2009
 
SATELLITE IMAGERY INDICATES THAT THE CLOUD PATTERN ASSOCIATED WITH
THE DEPRESSION HAS CONTINUED TO DETERIORATE...WITH THE NEAREST DEEP
CONVECTION NOW DISPLACED ABOUT 90 NM SOUTHEAST OF THE CENTER. SINCE
THE SYSTEM LACKS ORGANIZED DEEP CONVECTION...IT HAS NOW DEGENERATED
INTO A REMNANT LOW. THIS IS THE LAST ADVISORY ON TROPICAL
DEPRESSION ONE.
 
SINCE THE DEPRESSION IS MOVING OVER INCREASINGLY COLDER WATERS AND
UNDERGOING SIGNIFICANT WESTERLY SHEAR...NO REGENERATION IS
EXPECTED. THE REMNANTS OF THE DEPRESSION WILL BECOME ABSORBED
WITHIN A FRONTAL ZONE DEVELOPING NEAR AND NORTHEAST OF THE CENTER
LATER TONIGHT OR SATURDAY.

A DEEP LAYER OF SOUTHWESTERLY FLOW AHEAD OF A DEVELOPING TROUGH OVER
THE EASTERN UNITED STATES IS CARRYING THE REMNANTS OF THE
DEPRESSION STEADILY EAST-NORTHEASTWARD...065/16...AND MODELS SHOW
LITTLE CHANGE TO THIS HEADING OR SPEED.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/2100Z 40.3N  62.3W    25 KT...REMNANT LOW
 12HR VT     30/0600Z 41.4N  59.4W    25 KT...EXTRATROPICAL
 24HR VT     30/1800Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN/FRANKLIN
 

