WTNT44 KNHC 290843
TCDAT4
TROPICAL STORM MELISSA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
500 AM EDT SAT SEP 29 2007
 
DEEP CONVECTION HAS BEEN ON THE INCREASE DURING THE PAST SEVERAL
HOURS.  0319Z MICROWAVE IMAGERY INDICATED THAT THE CIRCULATION
CENTER WAS UNDER THE WESTERN PORTION OF THE CONVECTIVE CANOPY...BUT
SUBSEQUENT GOES IMAGES HINT THAT THE CONVECTION IS WRAPPING MORE
AROUND THE CENTER.  SUBJECTIVE DVORAK INTENSITY ESTIMATES AT 06Z
WERE A CONSENSUS 30 KT...BUT OBJECTIVE ESTIMATES ARE HIGHER AND
PROVIDE THE BASIS FOR UPGRADING THE SYSTEM TO A TROPICAL STORM WITH
35 KT MAXIMUM WINDS.
 
IT IS CLEAR THAT THE DEPRESSION IS BARELY MOVING...BUT THE EXACT
INITIAL MOTION IS STILL UNCERTAIN...ESTIMATED TO BE 270/3.  THE
CYCLONE IS EMBEDDED WITHIN VERY WEAK STEERING CURRENTS...LACKING A
SUBTROPICAL RIDGE TO ITS NORTH DUE TO A DEEP LAYER LOW PRESSURE
SYSTEM OVER THE NORTHEASTERN ATLANTIC.  AS THAT LOW PROCEEDS
EASTWARD...ALL OF THE MODELS DEPICT SOME RIDGING TO GRADUALLY BUILD
BACK IN OVER THE TROPICAL EASTERN ATLANTIC...BUT THEY DO NOT AGREE
ON HOW THE TRACK OF THE DEPRESSION WILL RESPOND.  THE HWRF PROVIDES
THE NORTHERNMOST SOLUTION...TAKING THE CYCLONE IMMEDIATELY
NORTHWESTWARD...WHILE THE ECMWF AND GFS ENSEMBLE MEAN ARE THE
SOUTHERN EXTREMES.  IN GENERAL...THE MODELS SEEM TO HAVE SHIFTED
AGAIN TO THE LEFT...AND SO HAS THE OFFICIAL FORECAST...WHICH CALLS
FOR THE CYCLONE TO MOVE IN A GENERAL WEST-NORTHWESTWARD DIRECTION
THROUGHOUT THE FIVE-DAY PERIOD.
 
THE DEPRESSION CURRENTLY RESIDES IN A RELATIVELY WEAK-SHEAR
ENVIRONMENT JUST TO THE SOUTH OF A BELT OF STRONG UPPER-LEVEL
WESTERLIES.  THE SHEAR WILL PROBABLY REMAIN WEAK ENOUGH TO ALLOW FOR
A LITTLE STRENGTHENING DURING THE NEXT 24-36 HOURS...BUT THEN IT
WILL BE ON THE INCREASE...ESPECIALLY BEYOND 48 HOURS WHEN
SIGNIFICANT WEAKENING IS EXPECTED.  THE OFFICIAL FORECAST PEAKS AT
40 KT...SLIGHTLY HIGHER THAN ALL OF THE OBJECTIVE GUIDANCE...BUT
CALLS FOR THE DEPRESSION TO DISSIPATE IN LESS THAN FIVE DAYS IN THE
HOSTILE ENVIRONMENT THAT LIES AHEAD LATER IN THE FORECAST PERIOD.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/0900Z 14.1N  27.4W    35 KT
 12HR VT     29/1800Z 14.4N  28.7W    35 KT
 24HR VT     30/0600Z 14.8N  30.5W    40 KT
 36HR VT     30/1800Z 15.5N  32.7W    40 KT
 48HR VT     01/0600Z 16.2N  34.8W    35 KT
 72HR VT     02/0600Z 17.5N  38.5W    30 KT
 96HR VT     03/0600Z 19.0N  42.0W    25 KT...DISSIPATING
120HR VT     04/0600Z 21.0N  45.0W    20 KT...REMNANT LOW
 
$$
FORECASTER KNABB
 

WTNT44 KNHC 291437
TCDAT4
TROPICAL STORM MELISSA DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
1100 AM EDT SAT SEP 29 2007
 
SHEAR CONTINUES TO BE A PROBLEM FOR STORMS IN THE DEEP TROPICS. THE
CENTER OF MELISSA HAS ALSO BECOME DETACHED FROM THE CONVECTION DUE
TO WESTERLY SHEAR. HOWEVER...THIS SHEAR PATTERN IS COMMON AT THE
END OF SEPTEMBER NEAR THE CAPE VERDE ISLANDS.  THE CLOUD PATTERN
STILL SUPPORTS TROPICAL STORM STATUS GIVEN THE LARGE AND WELL-
DEFINED CIRCULATION AND THE TIGHT SURFACE CENTER. SHEAR IS FORECAST
TO REMAIN MARGINAL FOR THE NEXT DAY OR SO...AND MELISSA COULD KEEP
ITS STORM STATUS. THEREAFTER...BOTH SHEAR AND A COOL OCEAN WILL
LIKELY TAKE A TOLL ON MELISSA. THE CYCLONE IS EXPECTED TO BE A
REMNANT LOW BY THE END OF THE FORECAST PERIOD IF NOT EARLIER.

MELISSA IS MOVING TOWARD THE NORTHWEST AT 7 KNOTS AROUND THE
PERIPHERY OF A MODEST SUBTROPICAL RIDGE. THIS RIDGE IS FORECAST TO
EXPAND A LITTLE AND THIS PATTERN WILL KEEP THE CYCLONE ON THIS
GENERAL TRACK. MOST OF THE GLOBAL MODELS DO NOT EVEN KNOW MELISSA
IS THERE...AND IF THEY KNOW...THEY DISSIPATE THE CYCLONE IN A DAY
OR TWO. THAT SEEMS LIKE A REASONABLE MODEL SOLUTION.

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/1500Z 15.2N  28.4W    35 KT
 12HR VT     30/0000Z 15.6N  29.4W    35 KT
 24HR VT     30/1200Z 16.5N  31.0W    35 KT
 36HR VT     01/0000Z 17.6N  33.4W    35 KT
 48HR VT     01/1200Z 18.5N  35.5W    30 KT
 72HR VT     02/1200Z 20.0N  39.1W    25 KT...DISSIPATING
 96HR VT     03/1200Z 21.5N  42.0W    20 KT...REMNANT LOW
120HR VT     04/1200Z 23.5N  45.0W    20 KT...REMNANT LOW
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 292031
TCDAT4
TROPICAL STORM MELISSA DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
500 PM EDT SAT SEP 29 2007
 
AFTER BEING EXPOSED FOR A FEW HOURS...NEW DEEP CONVECTION HAS
REGENERATED NEAR THE CENTER. SATELLITE INTENSITY ESTIMATES...
PRIMARILY OBJECTIVE T-NUMBERS FROM SAB AS WELL AS THOSE
PROVIDED BY UW-CIMSS INDICATE THAT MELISSA IS STILL A 35-KNOT
TROPICAL STORM. SINCE THE SHEAR IS FORECAST TO BE ABOUT 15 TO 20
KNOTS OVER MELISSA DURING THE NEXT DAY OR SO...THE CYCLONE COULD
KEEP ITS STORM STATUS FOR THAT PERIOD. THEREAFTER...BOTH SHEAR AND
A COOL OCEAN WILL LIKELY TAKE A TOLL ON MELISSA. THE CYCLONE IS
EXPECTED TO BE A REMNANT LOW BY THE END OF THE FORECAST PERIOD IF
NOT EARLIER.
 
MELISSA APPEARS TO BE MOVING TOWARD THE WEST-NORTHWEST OR 300
DEGREES AT 11 KNOTS AROUND THE PERIPHERY OF A MODEST SUBTROPICAL
RIDGE. THE RIDGE IS FORECAST TO EXPAND A LITTLE AND THIS PATTERN
WILL KEEP THE CYCLONE ON THIS GENERAL TRACK. IN THE LAST
RUN...MODELS KEEP MELISSA A LITTLE LONGER...AND ARE IN GOOD
AGREEMENT MOVING THE CYCLONE WEST-NORTHWESTWARD AROUND THE
PERIPHERY OF THE RIDGE. THE OFFICIAL FORECAST IS IN THE MIDDLE
OT THE GUIDANCE ENVELOPE. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      29/2100Z 15.6N  29.5W    35 KT
 12HR VT     30/0600Z 16.3N  30.9W    35 KT
 24HR VT     30/1800Z 17.0N  33.0W    35 KT
 36HR VT     01/0600Z 18.0N  35.0W    35 KT
 48HR VT     01/1800Z 19.0N  37.0W    30 KT
 72HR VT     02/1800Z 21.5N  41.0W    25 KT...DISSIPATING
 96HR VT     03/1800Z 24.0N  44.0W    20 KT...REMNANT LOW
120HR VT     04/1800Z 26.0N  45.0W    20 KT...REMNANT LOW
 
$$
FORECASTER AVILA
 

WTNT44 KNHC 300231
TCDAT4
TROPICAL STORM MELISSA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
1100 PM EDT SAT SEP 29 2007

VERY DEEP CONVECTION HAS BEEN PERSISTING NEAR MELISSA FOR THE PAST
SEVERAL HOURS...AND THE CENTER APPEARS TO BE JUST SOUTH OF A NEW
BURST OF THUNDERSTORMS.  SATELLITE INTENSITY ESTIMATES ARE
INCREASING A LITTLE...AND THE INITIAL INTENSITY WILL BE NUDGED
UPWARD TO 40 KT.  THIS INTENSIFICATION IS EXPECTED TO BE
SHORT-LIVED AS INCREASING WESTERLY SHEAR AFFECTS THE TROPICAL
CYCLONE.  A SLOW WEAKENING IS SHOWN IN THE NHC FORECAST... AND THEN
IS A LITTLE FASTER AFTER 36 HOURS AS THE SHIPS MODEL DIAGNOSES OVER
30 KT OF DESTRUCTIVE WESTERLY SHEAR.  MELISSA IS A SMALL TROPICAL
CYCLONE...AND SINCE SMALL STORMS ARE TYPICALLY MORE SUSCEPTIBLE TO
SHEAR...IT WOULD NOT BE SURPRISING FOR IT TO DISSIPATE FASTER THAN
SHOWN BELOW.
 
THE STORM APPEARS TO BE MOVING TOWARD THE WEST-NORTHWEST OR
295/8...BUT THERE IS A FAIR AMOUNT OF UNCERTAINTY DUE TO THE CENTER
BEING OBSCURED ON SATELLITE IMAGES.  A BUILDING RIDGE TO THE NORTH
OF MELISSA SHOULD KEEP THE STORM ON THE SAME GENERAL TRACK WITH A
SMALL ACCELERATION.  IF THE SYSTEM INTENSIFIES A BIT...IT MAY
BRIEFLY MOVE A LITTLE TO THE RIGHT...BUT THAT TRACK WOULD TAKE IT
OVER COOLER WATERS MORE QUICKLY.  THE OFFICIAL FORECAST IS BASICALLY
AN UPDATE TO THE PREVIOUS FORECAST...AND IS CLOSE TO A CONSENSUS OF
THE UMKET/GFDL/NOGAPS MODELS.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/0300Z 15.8N  30.2W    40 KT
 12HR VT     30/1200Z 16.5N  31.6W    40 KT
 24HR VT     01/0000Z 17.4N  33.7W    35 KT
 36HR VT     01/1200Z 18.4N  35.8W    35 KT
 48HR VT     02/0000Z 19.5N  38.0W    30 KT
 72HR VT     03/0000Z 22.0N  42.0W    25 KT...DISSIPATING
 96HR VT     04/0000Z 24.5N  44.5W    20 KT...REMNANT LOW
120HR VT     05/0000Z...DISSIPATED
 
$$
FORECASTER BLAKE
 

WTNT44 KNHC 300826
TCDAT4
TROPICAL STORM MELISSA DISCUSSION NUMBER   8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
500 AM EDT SUN SEP 30 2007
 
STRONG WESTERLY SHEAR IS GETTING THE BEST OF MELISSA AND THE
LOW-LEVEL CIRCULATION RECENTLY BECAME EXPOSED.  NEW CONVECTION HAS 
FORMED NEAR THE CIRCULATION CENTER BUT IS ALREADY SHOWING SIGNS OF
BEING SHUNTED EASTWARD.  BASED ON THE DEGRADED SATELLITE
PRESENTATION...THE INITIAL INTENSITY IS LOWERED TO 35 KT.  WITH THE
SHEAR EXPECTED TO INCREASE AND THE SSTS EXPECTED TO DECREASE IN A
DAY OR SO...MELISSA COULD STRUGGLE TO GENERATE PERSISTENT DEEP
CONVECTION AND MAINTAIN ITS STATUS AS A TROPICAL CYCLONE. 
DEGENERATION TO A REMNANT LOW IS EXPECTED IN ABOUT 3 DAYS...IF NOT
SOONER. 
 
MELISSA HAS PICKED UP FORWARD SPEED WITH THE INITIAL MOTION ESTIMATE
NOW 295/11.  THE TRACK FORECAST IS STRONGLY DEPENDENT ON HOW LONG
MELISSA CAN MAINTAIN APPRECIABLE VERTICAL DEPTH.  THE DYNAMICAL
MODELS ARE ESSENTIALLY SPLIT INTO TWO CAMPS.  THE NOGAPS AND UKMET
MODELS SHOW MELISSA REMAINING A RELATIVELY DEEP CYCLONE WITH A
SHARP NORTHEASTWARD TURN BEYOND 48 HOURS IN RESPONSE TO A MIDDLE- TO
UPPER-LEVEL TROUGH EXPECTED TO DEVELOP OVER THE CENTRAL ATLANTIC. 
THE WEAKER AND SHALLOWER HWRF AND ECMWF SOLUTIONS FOR THE CYCLONE
SHOW AN ALMOST INSTANT TURN WESTWARD.  SINCE THE OFFICIAL FORECAST
ASSUMES MELISSA WILL BE ABLE TO GENERATE INTERMITTENT BURSTS OF
CONVECTION DURING THE NEXT DAY OR TWO...THE TRACK FORECAST LIES IN
BETWEEN THESE TWO SCENARIOS BUT IS SOUTH OF THE DYNAMICAL MODEL
CONSENSUS. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/0900Z 16.5N  31.4W    35 KT
 12HR VT     30/1800Z 17.2N  33.0W    35 KT
 24HR VT     01/0600Z 18.3N  35.1W    30 KT
 36HR VT     01/1800Z 19.3N  37.1W    30 KT
 48HR VT     02/0600Z 20.5N  39.2W    30 KT
 72HR VT     03/0600Z 23.0N  42.5W    25 KT...REMNANT LOW
 96HR VT     04/0600Z 26.0N  44.5W    20 KT...REMNANT LOW
120HR VT     05/0600Z...DISSIPATED
 
$$
FORECASTER RHOME
 

WTNT44 KNHC 301442
TCDAT4
TROPICAL DEPRESSION MELISSA DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
1100 AM EDT SUN SEP 30 2007

STRONG WESTERLY SHEAR HAS TAKEN ITS TOLL ON MELISSA. AFTER MOST OF
THE CONVECTION DISSIPATED ABOUT 12 HOURS AGO...THE CYCLONE HAS ONLY
BEEN ABLE TO GENERATE SMALL PULSATING BURSTS OF CONVECTION THAT
HAVE EACH LASTED ABOUT 3 HOURS.  AN 0818 UTC QUIKSCAT PASS SUGGESTS
THAT THE CIRCULATION HAS BECOME LESS-DEFINED.  VISIBLE SATELLITE
IMAGERY REVEALS THAT WHATEVER CENTER REMAINS IS TO THE SOUTH OF
THE PREVIOUS ESTIMATES...REQUIRING A RELOCATION FOR THIS ADVISORY.
THE QUIKSCAT DATA SHOW THAT THE WINDS HAVE DECREASED TO ABOUT 25 KT
AND MELISSA IS DOWNGRADED TO A TROPICAL DEPRESSION. 

THE INITIAL MOTION ESTIMATE IS 285/11. SINCE MELISSA IS BECOMING A
SHALLOW SYSTEM IT SHOULD BE STEERED WEST-NORTHWESTWARD BY THE
LOW-LEVEL RIDGE OVER THE EASTERN ATLANTIC DURING THE NEXT DAY OR
SO. THEREAFTER...THE CYCLONE IS EXPECTED TO TURN NORTHWESTWARD
AROUND THE WESTERN PERIPHERY OF THIS RIDGE.  THE TRACK FORECAST HAS
BEEN SHIFTED SOUTHWARD MAINLY DUE TO THE RELOCATION...AND IS CLOSER
TO THE HWRF AND GFDL SOLUTIONS.

THE ENVIRONMENT AHEAD OF MELISSA IS EXPECTED TO REMAIN HOSTILE AS
WESTERLY SHEAR IS FORECAST TO PERSIST.  THE INTENSITY FORECAST
MAINTAINS MELISSA AS A TROPICAL DEPRESSION DURING THE NEXT DAY OR
SO.  HOWEVER...IF THE CIRCULATION CENTER CONTINUES TO BECOME
LESS DEFINED AND THE DEPRESSION DOES NOT GENERATE ENOUGH ORGANIZED
CONVECTION...IT COULD BECOME A REMNANT LOW MUCH SOONER.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/1500Z 16.1N  32.6W    25 KT
 12HR VT     01/0000Z 16.7N  34.3W    25 KT
 24HR VT     01/1200Z 17.7N  36.5W    25 KT
 36HR VT     02/0000Z 18.8N  38.9W    25 KT...REMNANT LOW
 48HR VT     02/1200Z 20.2N  40.8W    20 KT...REMNANT LOW
 72HR VT     03/1200Z 23.5N  43.5W    20 KT...REMNANT LOW
 96HR VT     04/1200Z...DISSIPATED
 
$$
FORECASTER BROWN
 

WTNT44 KNHC 302046
TCDAT4
TROPICAL DEPRESSION MELISSA DISCUSSION NUMBER  10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142007
500 PM EDT SUN SEP 30 2007

AS WAS THE CASE WITH INGRID...AND KAREN...WESTERLY SHEAR HAS CAUSED
ANOTHER TROPICAL CYCLONE IN THE ATLANTIC TO WEAKEN.

MELISSA HAS CONTINUED TO PRODUCE FEW VERY SMALL CLUSTERS OF
CONVECTION TODAY...EACH OF WHICH HAS LASTED ONLY A FEW HOURS.  
SINCE MELISSA HAS BEEN UNABLE TO PRODUCE ORGANIZED CONVECTION DURING
THE PAST 12-18 HOURS...IT NO LONGER CLASSIFIES AS A TROPICAL CYCLONE
AND THIS WILL BE THE LAST NHC ADVISORY.
 
THE INITIAL MOTION ESTIMATE IS 285/12.  THE REMNANT LOW IS EXPECTED
TO BE STEERED WEST-NORTHWESTWARD AROUND A LOW-LEVEL RIDGE OVER THE
EASTERN ATLANTIC.  THE REMNANT LOW...IF IT SURVIVES FOR A COUPLE OF
DAYS...MAY TURN MORE NORTHWESTWARD AS IT APPROACHES THE WESTERN
PERIPHERY OF THIS RIDGE.

ADDITIONAL INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER AWIPS
HEADER NFDHSFAT1 AND WMO HEADER FZNT01 KWBC.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/2100Z 16.3N  34.0W    25 KT
 12HR VT     01/0600Z 16.7N  35.9W    25 KT...REMNANT LOW
 24HR VT     01/1800Z 17.7N  38.3W    20 KT...REMNANT LOW
 36HR VT     02/0600Z 18.9N  40.7W    20 KT...REMNANT LOW
 48HR VT     02/1800Z 20.5N  42.8W    20 KT...REMNANT LOW
 72HR VT     03/1800Z...DISSIPATED
 
$$
FORECASTER BROWN
 

