00
WTNT44 KNHC 011453
TCDAT4
TROPICAL DEPRESSION NINE DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092010
1100 AM AST WED SEP 01 2010

THE VIGOROUS TROPICAL WAVE IN THE EASTERN TROPICAL ATLANTIC HAS
BECOME BETTER ORGANIZED WITH DEEP CONVECTION WRAPPING ALMOST HALF
WAY AROUND THE VORTEX.  CONSEQUENTLY...DVORAK INTENSITY ESTIMATES
FROM TAFB AND SAB SUPPORT INITIATING ADVISORIES ON THIS SYSTEM AS A
TROPICAL DEPRESSION.  AN ASCAT PASS AT 1126Z ALONG THE EDGE OF THE
CYCLONE INDICATED WINDS OF 25-30 KT.  THE INITIAL INTENSITY IS SET
AT 30 KT.

THE MOTION OF THE DEPRESSION IS 275 DEGREES AT 15 KT AS IT IS BEING
STEERED PRIMARILY BY A LARGE DEEP-LAYER SUBTROPICAL RIDGE TO ITS
NORTH. AS A STRONG MID-LATITUDE SHORT WAVE MOVES ACROSS THE NORTH
ATLANTIC...THE RIDGE WEAKENS SOME DURING THE NEXT TWO TO THREE
DAYS. THIS SHOULD RESULT IN A SLOWING OF THE CYCLONE AND A SLIGHT
TURN TOWARD THE WEST-NORTHWEST. BY DAYS FOUR AND FIVE...THE
SUBTROPICAL RIDGE RESTRENGTHENS AND THE DEPRESSION SHOULD
CORRESPONDINGLY ACCELERATE. THE GLOBAL MODELS ARE HAVING DIFFICULTY
DISTINGUISHING THE CYCLONE FROM THE PRONOUNCED MONSOON TROUGH IN
THE EASTERN ATLANTIC. THE FORECAST TRACK IS A BLEND OF THE
AVAILABLE GLOBAL MODELS...THE UKMET AND CANADIAN...AND THE GFDL AND
HWRF HURRICANE MODELS AND IS CLOSEST TO THE BAM-MEDIUM MODEL. THE
12Z GLOBAL MODEL GUIDANCE SHOULD PROVIDE A BETTER TRACK PREDICTION
SINCE THEY WILL HOPEFULLY HAVE A MORE REALISTIC HANDLE ON THE
INITIAL CONDITIONS OF THE DEPRESSION.

THE INTENSITY FORECAST...AS USUAL...IS QUITE UNCERTAIN. WHILE THE
DEPRESSION WILL BE TRAVERSING OVER VERY WARM WATERS...THE VERTICAL
SHEAR...ESPECIALLY THE MID-LEVEL CONTRIBUTION...IS MODERATE TO
STRONG. ADDITIONALLY...A LARGE OUTBREAK OF THE SAHARAN AIR LAYER IS
SITUATED JUST NORTH AND WEST OF THE DEPRESSION...WHICH MAY INHIBIT
SOME OF THE DEEP CONVECTION IN THE CORE OF THE SYSTEM. THE FORECAST
INTENSITY ONLY CALLS FOR GRADUALLY SPINNING THE CYCLONE UP AND IS
CLOSE TO THE FOUR-MODEL INTENSITY CONSENSUS. IT IS WORTH NOTING
THAT SOME OF THE GLOBAL MODELS...IN PARTICULAR THE GFS AND NOGAPS
DO NOT EVEN ACKNOWLEDGE THAT THE CYCLONE EXISTS NOW OR IN THE NEAR
FUTURE. HOWEVER...A QUICK DECAY OF THIS SYSTEM DOES NOT APPEAR TO
BE LIKELY.

FORECAST POSITIONS AND MAX WINDS

INITIAL      01/1500Z 12.4N  35.8W    30 KT
 12HR VT     02/0000Z 12.6N  37.8W    35 KT
 24HR VT     02/1200Z 13.0N  39.8W    35 KT
 36HR VT     03/0000Z 13.5N  41.4W    40 KT
 48HR VT     03/1200Z 14.0N  42.8W    40 KT
 72HR VT     04/1200Z 15.0N  45.0W    40 KT
 96HR VT     05/1200Z 16.0N  49.0W    45 KT
120HR VT     06/1200Z 17.0N  53.0W    50 KT

$$
FORECASTER LANDSEA/BLAKE

000
WTNT44 KNHC 012042
TCDAT4
TROPICAL STORM GASTON DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL092010
500 PM AST WED SEP 01 2010

THUNDERSTORMS HAVE CONSOLIDATED NEAR THE CENTER OF THE CYCLONE THIS
AFTERNOON...WITH AN INTENSE CONVECTIVE BAND IN THE WESTERN
SEMICIRCLE. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 45
KT AND 30 KT...RESPECTIVELY...WITH AMSU ESTIMATES FROM CIRA AND CSU
INDICATING 50 KT AND 37 KT. OVERALL THIS SYSTEM APPEARS BETTER
ORGANIZED THAN SIX HOURS AGO...AND A BLEND OF THESE DATA GIVES AN
INITIAL INTENSITY OF 35 KT...MAKING GASTON THE SEVENTH NAMED STORM
OF THE ATLANTIC HURRICANE SEASON.

THERE IS STILL A SIGNIFICANT AMOUNT OF DRY AIR TO THE WEST AND NORTH
OF THE TROPICAL STORM...WHICH MAY HINDER STRENGTHENING.  HOWEVER...
ALL OF THE GLOBAL MODELS SHOW THAT A RELATIVELY LIGHT SHEAR
ENVIRONMENT WILL BE PRESENT NEAR GASTON FOR THE NEXT SEVERAL DAYS.
THE GUIDANCE NOW INDICATES CONSIDERABLY MORE INTENSIFICATION OF
GASTON...WITH THE NORMALLY CONSERVATIVE LGEM SHOWING THIS SYSTEM
BECOMING A MAJOR HURRICANE BY THE END OF THE PERIOD.  THE NHC
FORECAST IS RAISED FROM THE PREVIOUS ONE...BUT REMAINS LOWER THAN
THE MODEL CONSENSUS.  

AN AMSR-E PASS AT 1613 UTC HELPED WITH THE INITIAL POSITION AND
MOTION...WHICH IS A BIT SLOWER THAN BEFORE AT 280/13. A SUBTROPICAL
RIDGE TO THE NORTH OF GASTON IS FORECAST TO WEAKEN SOON AS A
MID-LATITUDE TROUGH PASSES BY...WHICH WOULD CAUSE THE STORM TO SLOW
DOWN. THIS RIDGE SHOULD REBUILD IN A FEW DAYS AND STEER THE
TROPICAL STORM AT AN INCREASINGLY FASTER RATE TO THE WEST OR WEST-
NORTHWEST. GLOBAL MODELS HAVE COME INTO SOMEWHAT BETTER AGREEMENT
NOW THAT MOST OF THEM ARE INITIALIZING THE STORM...BUT THERE ARE
STILL SOME SIGNIFICANT SPEED DIFFERENCES. THE NHC FORECAST IS
FASTER THAN ALL OF THE GUIDANCE IN THE SHORT TERM AS IT SEEMS LIKE
THE MODELS ARE GENERALLY SHOWING TOO MUCH INTERACTION BETWEEN THE
ITCZ AND GASTON. THE NEW FORECAST DOES END UP CLOSE TO THE PREVIOUS
ONE BY DAY 5...AND IS NEAR A BLEND OF THE GFS/UKMET/HWRF/GFDL
MODELS.


FORECAST POSITIONS AND MAX WINDS

INITIAL      01/2100Z 12.9N  37.0W    35 KT
 12HR VT     02/0600Z 13.1N  38.3W    40 KT
 24HR VT     02/1800Z 13.4N  39.9W    40 KT
 36HR VT     03/0600Z 13.7N  41.2W    45 KT
 48HR VT     03/1800Z 14.0N  42.5W    50 KT
 72HR VT     04/1800Z 15.0N  45.5W    55 KT
 96HR VT     05/1800Z 15.5N  50.0W    65 KT
 120HR VT     06/1800Z 16.5N  54.5W    75 KT

$$
FORECASTER BLAKE

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