000 WTNT42 KNHC 070842 TCDAT2 SUBTROPICAL STORM OTTO DISCUSSION NUMBER 5 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL172010 500 AM AST THU OCT 07 2010 OTTO HAS BEEN STRUGGLING TO PRODUCE MUCH CONVECTION DURING THE OVERNIGHT HOURS. A CURVED OUTER BAND PERSISTS IN THE SOUTHERN SEMICIRCLE OF THE STORM...WITH A SMALL AMOUNT OF CONVECTION NEAR THE CENTER. SINCE THE CLOUD PATTERN HAS DETERIORATED A LITTLE BIT...THE MAXIMUM WINDS ARE REDUCED TO 50 KT...IN AGREEMENT WITH VARIOUS SATELLITE INTENSITY ESTIMATES FROM 35 TO 50 KT. IF THE CONVECTION NEAR THE CENTER CONTINUES...THEN OTTO WILL LIKELY TRANSITION INTO A TROPICAL STORM LATER TODAY. THE SYSTEM STILL HAS DAY OR TWO OF LIGHT SHEAR CONDITIONS AND WARM WATER TO INTENSIFY. IN FACT...ALL OF THE GUIDANCE SHOW OTTO BECOMING A HURRICANE...AND THE NHC FORECAST WILL GO ALONG WITH THAT SCENARIO. HOWEVER...OTTO PROBABLY NEEDS TO SHED ITS SUBTROPICAL CHARACTERISTICS TO TAKE ADVANTAGE OF THE FAVORABLE ENVIRONMENT. SINCE THE SYSTEM IS STILL RETAINING SOME SUBTROPICAL FEATURES...THE NHC FORECAST REMAINS BELOW THE MODEL CONSENSUS. GLOBAL MODELS SHOW OTTO BECOMING EMBEDDED WITHIN A FRONTAL ZONE BY 72 HR...SO EXTRATROPICAL STATUS IS INDICATED IN THE OFFICIAL FORECAST AT THAT TIME. THE STORM HAS NOT BEEN MOVING MUCH DURING THE PAST FEW HOURS AND IS ONLY DRIFTING NORTHWARD. INITIALLY...OTTO IS IN AN AREA OF LIGHT STEERING CURRENTS BETWEEN A DISTANT RIDGE OVER THE EAST-CENTRAL ATLANTIC OCEAN AND A MID-LATITUDE TROUGH OVER THE WESTERN ATLANTIC. THE TROUGH IS EXPECTED TO DIG SOUTHEASTWARD TODAY...WHICH SHOULD STEER OTTO MORE TO THE NORTHEAST AND CAUSE A FASTER FORWARD SPEED AS THE STORM MOVES IN FASTER FLOW BETWEEN THE RIDGE AND THE TROUGH. WHILE THE MODEL GUIDANCE REMAINS WELL CLUSTERED ON THIS SYNOPTIC PATTERN...THERE ARE SOME NOTABLE SPEED DIFFERENCES...AS THE GFDL/HWRF ARE MUCH FASTER THAN THE REST OF THE GUIDANCE. FOR NOW THE TRACK FORECAST WILL STAY CLOSER TO THE GLOBAL MODELS...SHOWING A SLOWER FORWARD MOTION...AND THE PREVIOUS NHC FORECAST. THE 96 AND 120 HR POSITIONS OF OTTO MAY HAVE TO BE ADJUSTED SOUTHWARD LATER TODAY DUE TO THE POSSIBILITY THAT THE CYCLONE GETS CAUGHT UP IN NORTHWESTERLY FLOW FROM A TROUGH EAST OF THE AZORES...RATHER THAN MID-LATITUDE SOUTHWESTERLY FLOW AS EARLIER MODEL RUNS WERE INDICATING. FORECAST POSITIONS AND MAX WINDS INITIAL 07/0900Z 23.6N 68.2W 50 KT 12HR VT 07/1800Z 24.0N 67.7W 55 KT 24HR VT 08/0600Z 25.1N 66.0W 60 KT 36HR VT 08/1800Z 26.8N 63.3W 65 KT 48HR VT 09/0600Z 28.8N 59.7W 60 KT 72HR VT 10/0600Z 33.5N 48.5W 55 KT...POST-TROP/EXTRATROP 96HR VT 11/0600Z 38.5N 35.0W 45 KT...POST-TROP/EXTRATROP 120HR VT 12/0600Z 41.0N 25.0W 35 KT...POST-TROP/EXTRATROP $$ FORECASTER BLAKE