Hurricane BILL

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HURRICANE BILL DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL032009
1100 AM AST MON AUG 17 2009
 
SATELLITE IMAGERY INDICATES THAT BILL CONTINUES TO INTENSIFY THIS
MORNING...WITH A UNIFORM CENTRAL DENSE OVERCAST AROUND THE CENTER.
THE INTENSITY IS RAISED TO 80 KT BASED ON A DVORAK T-NUMBER OF 4.5
FROM TAFB AT 1200 UTC. MICROWAVE IMAGERY FROM A 1132 UTC TRMM PASS
SHOWS SEVERAL CONVECTIVE BANDS SPIRALING AROUND THE CENTER...BUT NO
EVIDENCE OF AN EYE. BILL SHOULD PASS VERY CLOSE TO NOAA BUOY 41041
IN THE NEXT FEW HOURS...WHICH SHOULD HELP PROVIDE INFORMATION ON
THE WINDS AND CENTRAL PRESSURE OF THE CYCLONE. 

THE OCEANIC AND ATMOSPHERIC ENVIRONMENT CONTINUES TO BE FAVORABLE
FOR INTENSIFICATION. WHILE THE SHIPS RI INDEX SHOWS A 35 PERCENT
CHANCE OF AN INCREASE OF 30 KT OR MORE IN THE NEXT 24 HOURS...
MICROWAVE IMAGERY SUGGESTS THAT BILL DOES NOT YET HAVE A WELL
DEFINED INNER CORE STRUCTURE. THE OFFICIAL INTENSITY FORECAST
IS ABOVE THE PREVIOUS PACKAGE FOR THE FIRST 36 HOURS DUE TO THE
OBSERVED INTENSIFICATION AND IS IN BEST AGREEMENT WITH SHIPS AND
LGEM. BEYOND THAT TIME...THE STATISTICAL MODELS SHOW THE INTENSITY
LEVELING OFF...WHILE THE HWRF AND GFDL SHOW STRENGTHENING THROUGH
THE END OF THE PERIOD. GIVEN THIS UNCERTAINTY...THE OFFICIAL
FORECAST SHOWS A PEAK IN INTENSITY AT DAYS 3 AND 4...AND A SLIGHT
DECREASE AT DAY 5. 

BILL CONTINUES ON A HEADING OF 285/14...WITHIN THE DEEP-LAYER FLOW
OF A RIDGE EXTENDING WESTWARD OVER THE CENTRAL ATLANTIC FROM
AFRICA. GLOBAL MODELS AND WATER VAPOR IMAGERY INDICATE A PERSISTENT
MID-ATLANTIC TROUGH SITUATED ALONG 53W WHICH SHOULD CAUSE THE
CYCLONE TO TURN MORE TOWARD THE NORTHWEST BY DAY 3. BEYOND THIS
TIME...THE FLOW AROUND A LARGE MID- TO UPPER-LEVEL LOW THAT
DEVELOPS OVER THE EASTERN UNITED STATES SHOULD INDUCE A MORE
NORTH-NORTHWESTWARD TURN. ALL OF THE TRACK MODEL GUIDANCE...WITH
THE EXCEPTION OF THE UKMET...IS IN GOOD AGREEMENT ON THIS SCENARIO.
THE UKMET HAS A MUCH STRONGER SUBTROPICAL RIDGE THAN THE REST OF
THE GLOBAL MODELS AND THE GFS AND ECMWF ENSEMBLE MEANS. AS A
RESULT...THIS MODEL KEEPS BILL TOO FAR SOUTH TO FEEL THE EFFECTS OF
THE CLOSED LOW LATE IN THE PERIOD. THE OFFICIAL FORECAST IS
ESSENTIALLY AN UPDATE OF THE PREVIOUS PACKAGE THROUGH DAY 3...AND
IS SHIFTED SLIGHTLY TO THE RIGHT TOWARD THE MODEL CONSENSUS AT DAYS
4 AND 5. 

THE INITIAL 34-KT WIND RADII WERE MODIFIED BASED ON A 0920 UTC
QUIKSCAT PASS. 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/1500Z 14.1N  45.2W    80 KT
 12HR VT     18/0000Z 14.7N  47.5W    90 KT
 24HR VT     18/1200Z 15.5N  50.1W    95 KT
 36HR VT     19/0000Z 16.6N  52.6W   100 KT
 48HR VT     19/1200Z 18.0N  55.1W   105 KT
 72HR VT     20/1200Z 21.5N  60.0W   110 KT
 96HR VT     21/1200Z 26.0N  64.0W   110 KT
120HR VT     22/1200Z 31.5N  66.5W   105 KT
 
$$
FORECASTER BRENNAN/ROBERTS
 
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