Hurricane OTTO

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HURRICANE OTTO DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL172010
500 AM AST SAT OCT 09 2010
 
OTTO CONTINUES TO PRODUCE DEEP CONVECTION IN A CDO WITH CLOUD TOPS
COLDER THAN -80C...HOWEVER THE CLOUD PATTERN IS BECOMING
INCREASINGLY DISTORTED DUE TO 20 TO 25 KT OF SOUTHWESTERLY SHEAR.
THIS SHEAR IS ALSO TILTING THE VORTEX NORTHEASTWARD WITH HEIGHT AS
SEEN IN A 0021 UTC SSMIS PASS. THE INITIAL INTENSITY OF 75 KT IS
BASED ON A BLEND OF DVORAK FINAL-T AND CI NUMBERS OF 4.0 TO 5.0
FROM TAFB AND SAB. SLOW WEAKENING IS EXPECTED OVER THE NEXT DAY OR
SO WHILE OTTO REMAINS A TROPICAL CYCLONE DUE TO SHEAR AND
DECREASING SEA SURFACE TEMPERATURES. GRADUAL WEAKENING SHOULD
CONTINUE BEYOND THAT TIME AS OTTO UNDERGOES EXTRATROPICAL
TRANSITION.
 
THE INITIAL MOTION ESTIMATE OF 055/21 IS UNCERTAIN DUE TO A LACK OF
RECENT MICROWAVE IMAGERY...AND IS BASED ON THE ASSUMPTION THAT THE
LOW-LEVEL CENTER CONTINUES TO LAG BEHIND THE COLDEST CLOUD TOPS.
OTTO WILL CONTINUE ACCELERATING NORTHEASTWARD OVER THE NEXT COUPLE
OF DAYS BETWEEN A LARGE DEEP-LAYER TROUGH OFF THE COAST OF NORTH
AMERICA AND A SUBTROPICAL RIDGE OVER THE EASTERN TROPICAL ATLANTIC.
THE OFFICIAL FORECAST IS A BLEND OF THE PREVIOUS PACKAGE AND THE
TVCN MULTI-MODEL CONSENSUS THROUGH 48 HOURS. BEYOND THAT TIME...
MOST OF THE GLOBAL MODELS AND THE GFS ENSEMBLE MEAN SUGGEST THAT
POST-TROPICAL OTTO WILL MOVE AROUND THE TOP OF A SHORTWAVE RIDGE
AND TURN SOUTHEASTWARD IN THE VICINITY OF THE AZORES. HOWEVER...
THERE ARE DIFFERENCES IN BOTH THE SHARPNESS OF THE SOUTHEASTWARD
TURN AND THE FORWARD SPEED. THE OFFICIAL FORECAST HAS BEEN ADJUSTED
SOUTHWARD AND WESTWARD AT DAYS 4 AND 5 TOWARD A BLEND OF THE UKMET
AND GFS MODELS...BUT CONFIDENCE IS LOWER THAN NORMAL AT THESE TIMES
DUE TO THE LARGE SPREAD IN THE GUIDANCE.
 
THE INITIAL 34-KT WIND RADII WERE ADJUSTED BASED ON A 0052 UTC ASCAT
PASS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      09/0900Z 29.2N  58.5W    75 KT
 12HR VT     09/1800Z 31.1N  54.8W    70 KT
 24HR VT     10/0600Z 34.3N  48.3W    70 KT
 36HR VT     10/1800Z 37.7N  40.8W    65 KT
 48HR VT     11/0600Z 41.3N  33.4W    55 KT...POST-TROP/EXTRATROP
 72HR VT     12/0600Z 43.0N  27.0W    45 KT...POST-TROP/EXTRATROP
 96HR VT     13/0600Z 40.5N  24.5W    40 KT...POST-TROP/EXTRATROP
120HR VT     14/0600Z 37.0N  22.0W    40 KT...POST-TROP/EXTRATROP
 
$$
FORECASTER BRENNAN
 
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