000
WTNT41 KNHC 132038
TCDAT1
HURRICANE IGOR DISCUSSION NUMBER  23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
500 PM AST MON SEP 13 2010

THE STRUCTURE OF IGOR HAS CHANGED LITTLE OVER THE PAST FEW HOURS.
THE EYE REMAINS VERY DISTINCT IN IR AND VISIBLE IMAGERY...AND
ALTHOUGH THE TOPS SURROUNDING THE EYE HAVE WARMED A BIT...DVORAK
CLASSIFICATIONS STILL SUPPORT AN INTENSITY OF 130 KT.  IGOR WILL
REMAIN IN A FAVORABLE ENVIRONMENT FOR MAINTAINING ITS CURRENT
INTENSITY FOR THE NEXT COUPLE OF DAYS...AND THE OFFICIAL FORECAST
DOES NOT SHOW ANY WEAKENING UNTIL AFTER 48 HOURS.  WHILE A 1640 UTC
AMSR-E PASS DOES NOT SHOW ANY EVIDENCE OF A SECONDARY EYEWALL
YET...IT IS POSSIBLE THAT AN EYEWALL REPLACEMENT CYCLE WILL OCCUR
IN THE FIRST COUPLE OF DAYS...WHICH COULD RESULT IN SOME INTENSITY
FLUCTUATIONS NOT REPRESENTED IN THE OFFICIAL FORECAST.  BEYOND 36
HOURS...ALL OF THE INTENSITY GUIDANCE SUGGEST THAT SLOW WEAKENING
SHOULD BEGIN...ALTHOUGH THERE ARE NO OVERLY NEGATIVE FACTORS UNTIL
THE VERY END OF THE PERIOD WHEN THE VERTICAL SHEAR MAY INCREASE.
THE OFFICIAL FORECAST SHOWS A GRADUAL WEAKENING AT DAYS 3 THROUGH 5
BUT IS HIGHER THAN MOST OF THE GUIDANCE THROUGH THE PERIOD.

THE INITIAL MOTION IS STILL DUE WEST...270 DEGREES...AT 9 KNOTS.
ALL OF THE GUIDANCE...EXCEPT THE UKMET...INSISTS ON A TURN TOWARD
THE WEST-NORTHWEST IN THE NEXT 12 HOURS AS IGOR BEGINS TO MOVE INTO
A LARGE WEAKNESS IN THE SUBTROPICAL RIDGE.  HOWEVER...DUE TO THE
INITIAL POSITION AND MOTION...THE OFFICIAL FORECAST HAS AGAIN BEEN
ADJUSTED A LITTLE TO THE LEFT OF THE PREVIOUS ADVISORY THROUGH 48
HOURS.  BEYOND THAT TIME...THERE IS STILL SOME SPREAD IN THE TRACK
GUIDANCE.  THE ECMWF AND UKMET STILL SHOW A STRONGER RIDGE NORTH OF
IGOR THROUGH MUCH OF THE PERIOD...TAKING THE CYCLONE FARTHER WEST
THAN THE REST OF THE GUIDANCE.  THE GFS AND GFDL CONTINUE TO SHOW
THE LEAST RIDGING AND TURN IGOR NORTH-NORTHWESTWARD AT THE END OF
THE PERIOD AHEAD OF A MID-LATITUDE TROUGH.  WHILE CONFIDENCE IN THE
TRACK FORECAST LATE IN THE PERIOD REMAINS LOW...THE GUIDANCE SHOWS
A LITTLE LESS SPREAD NOW THAN EARLIER TODAY.  THE NEW OFFICIAL
FORECAST SHOWS A NORTHWESTWARD MOTION AT DAYS 3 THROUGH 5...AND IS
SIMILAR TO THE PREVIOUS FORECAST.  THIS ENDS UP BEING VERY CLOSE TO
THE TVCN MULTI-MODEL CONSENSUS AND A BLEND OF THE GFS AND ECMWF
MODELS.

LARGE SWELLS FROM IGOR WILL BEGIN AFFECTING THE LEEWARD ISLANDS
TOMORROW AND REACH PUERTO RICO AND THE VIRGIN ISLANDS BY WEDNESDAY.  

FORECAST POSITIONS AND MAX WINDS

INITIAL      13/2100Z 17.7N  50.5W   130 KT
 12HR VT     14/0600Z 18.1N  51.7W   130 KT
 24HR VT     14/1800Z 18.9N  53.2W   130 KT
 36HR VT     15/0600Z 20.0N  54.7W   130 KT
 48HR VT     15/1800Z 21.1N  56.1W   130 KT
 72HR VT     16/1800Z 23.5N  58.5W   120 KT
 96HR VT     17/1800Z 26.5N  61.5W   110 KT
120HR VT     18/1800Z 30.0N  64.0W   105 KT

$$
FORECASTER BRENNAN

000
WTNT41 KNHC 140246
TCDAT1
HURRICANE IGOR DISCUSSION NUMBER  24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 PM AST MON SEP 13 2010

MICROWAVE AND GEOSTATIONARY SATELLITE IMAGERY SUGGESTS THAT AN
EYEWALL REPLACEMENT CYCLE MAY HAVE BEGUN.  TRMM...WINDSAT...AND
SSMIS PASSES FROM ABOUT 5-6 HOURS AGO ALL INDICATED THAT A
SECONDARY EYEWALL WAS BEGINNING TO FORM...AND MORE RECENTLY
CONVECTIVE TOPS AROUND THE EYE HAVE BEEN WARMING.  SUBJECTIVE
DVORAK FINAL-T ESTIMATES HAD FALLEN TO T6.0 TAFB AND SAB AT 0000
UTC...AND THE LATEST OBJECTIVE ADT ESTIMATE IS T6.0/6.4.  BASED ON
THESE DATA...THE INITIAL INTENSITY IS LOWERED TO 120 KT.  FOLLOWING
A CONSENSUS OF THE INTENSITY GUIDANCE...THE OFFICIAL FORECAST KEEPS
IGOR AT THIS INTENSITY FOR THE NEXT 24 HOURS OR SO...BUT IT IS
POSSIBLE THAT ADDITIONAL WEAKENING COULD OCCUR WHILE THE EYEWALL
REPLACEMENT IS IN PROGRESS.  SINCE IGOR IS STILL EXPECTED TO BE
OVER WARM OCEAN WATERS AND REMAIN IN A LOW SHEAR ENVIRONMENT...THE
FORECAST ALLOWS FOR THE POSSIBILITY OF SOME RE-STRENGTHENING
BETWEEN 36-48 HOURS...WHICH IS HINTED AT IN THE SHIPS OUTPUT.
WEAKENING IS THEN INDICATED DURING DAYS 3 THROUGH 5...BUT IT IS
CONSERVATIVE AND STILL LIES JUST ABOVE THE UPPER BOUND OF THE
GUIDANCE.

IGOR JUST WILL NOT BUDGE VERY MUCH TO THE NORTH AND IS MOVING 275
DEGREES AT 8 KT.  THE UKMET MODEL HAS CAPTURED THIS MOTION WELL
OVER THE PAST COUPLE OF DAYS AND HAS CONSISTENTLY BEEN LOCATED ON
THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE.  SINCE THERE IS STILL
NO CLEAR EVIDENCE OF THE BEGINNING OF A TURN...THE NHC FORECAST
TRACK LIES ALONG THE SOUTHERN PERIPHERY OF THE TRACK GUIDANCE FOR
THE FIRST 24 HOURS...ALTHOUGH STILL NOT AS FAR SOUTH AS THE UKMET.
A TURN TOWARD THE NORTHWEST IS EXPECTED BY 36 HOURS WHEN IGOR
SHOULD HAVE REACHED THE BREAK IN THE SUBTROPICAL RIDGE.  THE SPREAD
IN THE MODELS FROM DAYS 3 THROUGH 5 HAS AGAIN TIGHTENED...AND THE
OFFICIAL FORECAST IS CHANGED LITTLE FROM THE PREVIOUS ONE.  THIS
FORECAST ALSO LIES CLOSE TO A MULTI-MODEL CONSENSUS THAT EXCLUDES
THE GFDN...WHICH HAS BEEN FASTER THAN THE OTHER GUIDANCE FOR
SEVERAL CYCLES.

LARGE SWELLS FROM IGOR WILL BEGIN AFFECTING THE LEEWARD ISLANDS
TOMORROW AND REACH PUERTO RICO AND THE VIRGIN ISLANDS BY WEDNESDAY.


FORECAST POSITIONS AND MAX WINDS

INITIAL      14/0300Z 17.7N  51.2W   120 KT
 12HR VT     14/1200Z 18.0N  52.3W   120 KT
 24HR VT     15/0000Z 18.8N  53.7W   120 KT
 36HR VT     15/1200Z 19.9N  55.2W   125 KT
 48HR VT     16/0000Z 21.1N  56.6W   125 KT
 72HR VT     17/0000Z 24.0N  59.5W   115 KT
 96HR VT     18/0000Z 27.0N  62.5W   105 KT
120HR VT     19/0000Z 30.5N  64.5W    95 KT

$$
FORECASTER BERG