000 WTNT42 KNHC 180238 TCDAT2 TROPICAL STORM BRET DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022011 1100 PM EDT SUN JUL 17 2011 THE AIR FORCE HURRICANE HUNTER AIRCRAFT MADE TWO ADDITIONAL PASSES THROUGH THE CENTER OF THE TROPICAL CYCLONE AFTER THE RELEASE OF THE 2100 UTC NHC ADVISORY. DURING THOSE PASSES...PEAK FLIGHT-LEVEL WINDS OF 43-45 KT WERE RECORDED ALONG WITH A FEW BELIEVABLE SFMR SURFACE WINDS JUST ABOVE TROPICAL STORM FORCE. BASED ON THESE OBSERVATIONS AND THE DEVELOPMENT OF NEW CONVECTION JUST NORTHEAST OF THE CENTER AROUND 0000 UTC...THE DEPRESSION WAS UPGRADED TO A TROPICAL STORM AT THAT TIME. MICROWAVE AND SATELLITE IMAGERY SHOW THAT MOST OF THE ASSOCIATED DEEP CONVECTION IS LOCATED OVER THE EASTERN SEMICIRCLE OF THE CIRCULATION DUE TO MODERATE WESTERLY SHEAR. THE SHEAR IS FORECAST TO DECREASE SLIGHTLY DURING THE NEXT 12-24 HOURS...WHICH SHOULD ALLOW AN OPPORTUNITY FOR SOME STRENGTHENING. THE NHC INTENSITY FORECAST IS IN GOOD AGREEMENT WITH THE SHIPS/LGEM GUIDANCE AND SHOWS PEAK INTENSITY OCCURRING BETWEEN 24-36 HOURS. WEAKENING IS INDICATED BEYOND 36 HOURS WHEN THE GLOBAL MODELS PREDICT AN INCREASE IN UPPER-LEVEL NORTHEASTERLY WINDS OVER THE CYCLONE. BRET HAS BEEN DRIFTING EASTWARD DURING THE PAST FEW HOURS...BUT A LONGER-TERM MOTION YIELDS 145/2. THE TROPICAL STORM IS NOT FORECAST TO MOVE VERY MUCH DURING THE NEXT 12-18 HOURS AS IT REMAINS IN AN AREA OF WEAK STEERING CURRENTS. IN 24-36 HOURS...THE RIDGE TO THE SOUTHEAST OF BRET IS FORECAST TO STRENGTHEN WHICH SHOULD PRODUCE A NORTHEASTWARD MOTION. AS BRET GAINS LATITUDE IN 2-3 DAYS...IT SHOULD ACCELERATE EAST-NORTHEASTWARD WITHIN AN AREA OF DEEP-LAYER WESTERLY FLOW. THE LATEST HWRF AND GFDL MODEL FORECASTS SHOW A MORE NORTH-NORTHEASTWARD MOTION WITH A TRACK MUCH CLOSER TO THE UNITED STATES THAN THE USUALLY RELIABLE ECMWF AND GFS MODELS. THIS SCENARIO APPEARS UNLIKELY DUE TO THE STRENGTH OF THE MID- TO UPPER-LEVEL RIDGE FORECAST OVER THE CENTRAL UNITED STATES. FOR NOW...THE OFFICIAL FORECAST PLACES MORE WEIGHT ON THE GLOBAL MODELS AND IS VERY SIMILAR TO THE PREVIOUS NHC TRACK. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 27.5N 78.0W 35 KT 40 MPH 12H 18/1200Z 27.7N 77.9W 40 KT 45 MPH 24H 19/0000Z 28.5N 77.4W 50 KT 60 MPH 36H 19/1200Z 29.7N 76.7W 50 KT 60 MPH 48H 20/0000Z 30.7N 75.5W 45 KT 50 MPH 72H 21/0000Z 32.5N 71.5W 40 KT 45 MPH 96H 22/0000Z 34.5N 65.5W 35 KT 40 MPH 120H 23/0000Z 36.5N 58.5W 30 KT 35 MPH $$ FORECASTER BROWN/BERG 000 WTNT42 KNHC 180238 TCDAT2 TROPICAL STORM BRET DISCUSSION NUMBER 2 NWS NATIONAL HURRICANE CENTER MIAMI FL AL022011 1100 PM EDT SUN JUL 17 2011 THE AIR FORCE HURRICANE HUNTER AIRCRAFT MADE TWO ADDITIONAL PASSES THROUGH THE CENTER OF THE TROPICAL CYCLONE AFTER THE RELEASE OF THE 2100 UTC NHC ADVISORY. DURING THOSE PASSES...PEAK FLIGHT-LEVEL WINDS OF 43-45 KT WERE RECORDED ALONG WITH A FEW BELIEVABLE SFMR SURFACE WINDS JUST ABOVE TROPICAL STORM FORCE. BASED ON THESE OBSERVATIONS AND THE DEVELOPMENT OF NEW CONVECTION JUST NORTHEAST OF THE CENTER AROUND 0000 UTC...THE DEPRESSION WAS UPGRADED TO A TROPICAL STORM AT THAT TIME. MICROWAVE AND SATELLITE IMAGERY SHOW THAT MOST OF THE ASSOCIATED DEEP CONVECTION IS LOCATED OVER THE EASTERN SEMICIRCLE OF THE CIRCULATION DUE TO MODERATE WESTERLY SHEAR. THE SHEAR IS FORECAST TO DECREASE SLIGHTLY DURING THE NEXT 12-24 HOURS...WHICH SHOULD ALLOW AN OPPORTUNITY FOR SOME STRENGTHENING. THE NHC INTENSITY FORECAST IS IN GOOD AGREEMENT WITH THE SHIPS/LGEM GUIDANCE AND SHOWS PEAK INTENSITY OCCURRING BETWEEN 24-36 HOURS. WEAKENING IS INDICATED BEYOND 36 HOURS WHEN THE GLOBAL MODELS PREDICT AN INCREASE IN UPPER-LEVEL NORTHEASTERLY WINDS OVER THE CYCLONE. BRET HAS BEEN DRIFTING EASTWARD DURING THE PAST FEW HOURS...BUT A LONGER-TERM MOTION YIELDS 145/2. THE TROPICAL STORM IS NOT FORECAST TO MOVE VERY MUCH DURING THE NEXT 12-18 HOURS AS IT REMAINS IN AN AREA OF WEAK STEERING CURRENTS. IN 24-36 HOURS...THE RIDGE TO THE SOUTHEAST OF BRET IS FORECAST TO STRENGTHEN WHICH SHOULD PRODUCE A NORTHEASTWARD MOTION. AS BRET GAINS LATITUDE IN 2-3 DAYS...IT SHOULD ACCELERATE EAST-NORTHEASTWARD WITHIN AN AREA OF DEEP-LAYER WESTERLY FLOW. THE LATEST HWRF AND GFDL MODEL FORECASTS SHOW A MORE NORTH-NORTHEASTWARD MOTION WITH A TRACK MUCH CLOSER TO THE UNITED STATES THAN THE USUALLY RELIABLE ECMWF AND GFS MODELS. THIS SCENARIO APPEARS UNLIKELY DUE TO THE STRENGTH OF THE MID- TO UPPER-LEVEL RIDGE FORECAST OVER THE CENTRAL UNITED STATES. FOR NOW...THE OFFICIAL FORECAST PLACES MORE WEIGHT ON THE GLOBAL MODELS AND IS VERY SIMILAR TO THE PREVIOUS NHC TRACK. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 27.5N 78.0W 35 KT 40 MPH 12H 18/1200Z 27.7N 77.9W 40 KT 45 MPH 24H 19/0000Z 28.5N 77.4W 50 KT 60 MPH 36H 19/1200Z 29.7N 76.7W 50 KT 60 MPH 48H 20/0000Z 30.7N 75.5W 45 KT 50 MPH 72H 21/0000Z 32.5N 71.5W 40 KT 45 MPH 96H 22/0000Z 34.5N 65.5W 35 KT 40 MPH 120H 23/0000Z 36.5N 58.5W 30 KT 35 MPH $$ FORECASTER BROWN/BERG