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Tropical Depression GABRIELLE Forecast Discussion Number 4

2013-09-05 16:41:30| National Hurricane Center (Atlantic)

Issued at 1100 AM AST THU SEP 05 2013 000 WTNT42 KNHC 051441 TCDAT2 TROPICAL DEPRESSION GABRIELLE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST THU SEP 05 2013 A COMBINATION OF SATELLITE...SAN JUAN DOPPLER RADAR...RAWINSONDE... AND AIRCRAFT DATA INDICATES THAT GABRIELLE HAS BECOME VERY DISORGANIZED. THE LOW-LEVEL CENTER...WHICH IS POORLY DEFINED...IS LOCATED SOUTH OF THE MONA PASSAGE ABOUT 130 N MI FROM THE MID-LEVEL CENTER THAT IS LOCATED BETWEEN PUERTO RICO AND THE VIRGIN ISLANDS. THIS STRUCTURE MAY BE DUE TO SOME WESTERLY VERTICAL WIND SHEAR... ALTHOUGH THE SHEAR APPEARS TO BE TOO LIGHT TO HAVE SUCH A DRASTIC EFFECT ON THE CYCLONE. NONE OF THE DATA CURRENTLY SUGGEST TROPICAL STORM FORCE WINDS ARE OCCURRING...SO GABRIELLE IS DOWNGRADED TO A 30-KT TROPICAL DEPRESSION. CONVECTION CONTINUES NEAR THE MID-LEVEL CENTER...SO THERE IS STILL A CHANCE OF THE LOW-LEVEL CENTER REFORMING IN THAT AREA. IF THAT DOES NOT OCCUR...GABRIELLE IS EXPECTED TO WEAKEN AS IT INTERACTS WITH THE TERRAIN OF THE DOMINICAN REPUBLIC AND ENCOUNTERS INCREASING WESTERLY SHEAR. THE REVISED INTENSITY FORECAST NOW CALLS FOR THE CYCLONE TO DEGENERATE TO A REMNANT LOW PRESSURE AREA IN 24 HOURS AND TO DISSIPATE COMPLETELY THEREAFTER. THE INITIAL MOTION IS AN UNCERTAIN 305/8. LOW-LEVEL RIDGING NORTH AND NORTHEAST OF GABRIELLE SHOULD ALLOW THIS GENERAL MOTION TO CONTINUE UNTIL THE CYCLONE DISSIPATES. IF THE SYSTEM SURVIVES LONGER THAN CURRENTLY FORECAST...THE DYNAMICAL MODELS SUGGEST IT WILL TURN NORTHWARD IN RESPONSE TO A DEVELOPING DEEP-LAYER TROUGH OVER THE WESTERN ATLANTIC. A HEAVY RAIN THREAT CONTINUES OVER PUERTO RICO AND THE VIRGIN ISLANDS. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 17.5N 68.1W 30 KT 35 MPH 12H 06/0000Z 18.3N 68.8W 25 KT 30 MPH 24H 06/1200Z 19.6N 69.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 07/0000Z...DISSIPATED $$ FORECASTER BEVEN

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Tropical Depression TWELVE-E Forecast Discussion Number 2

2013-09-05 16:39:31| Tropical Depression LIDIA

Issued at 800 AM PDT THU SEP 05 2013

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Tropical Depression TWELVE-E Forecast Discussion Number 1

2013-09-05 10:45:59| Tropical Depression LIDIA

Issued at 200 AM PDT THU SEP 05 2013

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Tropical Storm GABRIELLE Forecast Discussion Number 3

2013-09-05 10:41:36| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 05 2013 000 WTNT42 KNHC 050841 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST THU SEP 05 2013 ALTHOUGH THE AREA OF DEEP CONVECTION HAS EXPANDED SIGNIFICANTLY DURING THE PAST SEVERAL HOURS AND THE OUTFLOW IS EXCELLENT... SURROUNDING SURFACE OBSERVATIONS DO NOT SUGGEST THAT THERE HAS BEEN ANY IMPROVEMENT OF THE CIRCULATION. IN ADDITION...MICROWAVE OR DOPPLER RADAR DATA DO NOT SHOW ANY DEVELOPMENT OF AN INNER CORE...ALTHOUGH RADAR IMAGES SHOW A WELL-DEFINED MID-LEVEL CENTER TO THE EAST OF THE SURFACE LOCATION. I WOULD NOT BE SURPRISED IF THERE IS A REFORMATION OF THE SURFACE CENTER. A RECONNAISSANCE PLANE LATER THIS MORNING WILL HELP US TO DETERMINE IF THIS IS THE CASE. SUBJECTIVE ESTIMATES FROM TAFB AND SAB AS WELL AS OBJECTIVE ESTIMATES FROM THE UNIVERSITY OF WISCONSIN...CIMSS...ARE 2.5 ON THE DVORAK SCALE. ON THIS BASIS...THE INITIAL INTENSITY IS KEPT AT 35 KNOTS...AND THESE WINDS ARE PROBABLY CONFINED TO A VERY SMALL AREA NEAR THE CENTER. THE INTENSITY FORECAST IS HIGHLY UNCERTAIN. MOST OF THE GLOBAL MODELS KEEP A WEAK CYCLONE FOR A FEW DAYS WITH THE EXCEPTION OF THE ECMWF WHICH DISSIPATES GABRIELLE JUST NORTH OF HISPANIOLA IN A COUPLE OF DAYS. GIVEN THE STRONG WESTERLY SHEAR WHICH IS FORECAST TO BECOME ESTABLISHED ALONG THE FORECAST PATH OF GABRIELLE...THE DISSIPATION OPTION OF THE ECMWF IS NOT OUT OF THE QUESTION. AT THIS TIME...THE NHC FORECAST FOLLOWS THE MODEL CONSENSUS SHOWING SOME SLIGHT STRENGTHENING GIVING CREDIT TO THE OTHER MODELS. ALTHOUGH THE SURFACE CENTER IS DIFFICULT TO FIND ON IR IMAGES...IT APPEARS TO BE ON THE WESTERN EDGE OF THE DEEP CONVECTION. THE BEST ESTIMATE OF THE INITIAL MOTION IS TOWARD THE NORTHWEST OR 320 DEGREES AT 7 KNOTS. GABRIELLE IS EMBEDDED WITHIN A WEAK STEERING FLOW SOUTH OF A NARROW RIDGE OF HIGH PRESSURE OVER THE WESTERN ATLANTIC. IN A DAY OR TWO...A MID-LEVEL TROUGH IS FORECAST TO MOVE FROM THE UNITED STATES EASTWARD ACROSS THE ATLANTIC...CAUSING GABRIELLE TO RECURVE AND MOVE TOWARD THE OPEN ATLANTIC. THE OFFICIAL FORECAST IS VERY CLOSE TO THE MULTI-MODEL CONSENSUS AND IS NOT TOO DIFFERENT FROM THE PREVIOUS ONE. REGARDLESS OF THE EXACT TRACK OF THE CENTER OF GABRIELLE DURING THE NEXT 24 HOURS...THE MAIN THREAT WILL BE HEAVY RAINFALL OVER PORTIONS OF PUERTO RICO AND THE EASTERN PORTION OF THE DOMINICAN REPUBLIC. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 17.5N 66.9W 35 KT 40 MPH 12H 05/1800Z 18.5N 67.7W 35 KT 40 MPH 24H 06/0600Z 19.7N 68.5W 40 KT 45 MPH 36H 06/1800Z 20.9N 69.1W 45 KT 50 MPH 48H 07/0600Z 21.8N 69.5W 50 KT 60 MPH 72H 08/0600Z 24.0N 69.0W 50 KT 60 MPH 96H 09/0600Z 27.0N 66.0W 50 KT 60 MPH 120H 10/0600Z 31.5N 62.5W 50 KT 60 MPH $$ FORECASTER AVILA

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Tropical Depression SEVEN Forecast Discussion Number 1

2013-09-04 22:58:08| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED SEP 04 2013 000 WTNT42 KNHC 042057 TCDAT2 TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 PM AST WED SEP 04 2013 AIRCRAFT AND SATELLITE DATA FROM THIS AFTERNOON INDICATE THAT THE LOW PRESSURE SYSTEM SOUTH OF PUERTO RICO HAS JUST ENOUGH OF A CIRCULATION AND ORGANIZED CONVECTION TO BE CONSIDERED A TROPICAL DEPRESSION. THE INITIAL INTENSITY IS SET TO 30 KT BASED ON A 41 KT FLIGHT-LEVEL WIND FROM THE AIR FORCE PLANE. THE ENVIRONMENT NEAR THE DEPRESSION APPEARS TO BE CONDUCIVE FOR STRENGTHENING DURING THE NEXT DAY OR SO WHILE IT REMAINS FAR ENOUGH AWAY FROM HISPANIOLA. ONLY GRADUAL INTENSIFICATION IS FORECAST DUE TO THE SOMEWHAT DISORGANIZED INITIAL STATE OF THE DEPRESSION. AFTER THAT TIME...A COMBINATION OF INCREASING VERTICAL WIND SHEAR AND POSSIBLE LAND INTERACTION COULD SLOW THE DEVELOPMENT OF THE CYCLONE. THE NHC FORECAST IS ON THE LOW SIDE OF THE GUIDANCE ENVELOPE...AND IS CLOSER TO THE SHIPS AND LGEM MODELS. THE WIND SPEED PREDICTION ALSO FITS THE GENERAL IDEA OF THE GLOBAL MODELS...WHICH SUGGEST THAT THE CYCLONE WILL STRUGGLE AFTER IT LEAVES THE CARIBBEAN SEA. SOME INTENSIFICATION...PERHAPS DUE TO BAROCLINIC PROCESSES...IS POSSIBLE AT LONG RANGE AS THE CYCLONE INTERACTS WITH A MID-LATITUDE TROUGH. THE DEPRESSION APPEARS TO BE MOVING ROUGHLY 305/8 AROUND THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE OVER THE CENTRAL ATLANTIC OCEAN. A LARGE TROUGH OVER THE WESTERN ATLANTIC OCEAN IS EXPECTED TO CAUSE THE RIDGE TO BREAK ALONG ABOUT 70W...WHICH SHOULD CAUSE THE CYCLONE TO TURN NORTHWARD IN TWO OR THREE DAYS. ONE COMPLICATING FACTOR IS THE LARGER DISTURBANCE LOCATED A FEW HUNDRED MILES NORTHEAST OF THE DEPRESSION. THE INTERACTION OF THESE TWO FEATURES MAKES THIS TRACK FORECAST MORE UNCERTAIN THAN WOULD BE SUGGESTED BY THE OVERALL MODEL SPREAD. THE NHC FORECAST IS NOT TOO FAR FROM THE MODEL CONSENSUS EARLY ON...AND THEN IS A BIT SLOWER THAN THE CONSENSUS AFTER THAT TIME...PUTTING LESS WEIGHT ON THE NORTHWARD GFDL/HWRF SOLUTIONS. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 16.5N 66.2W 30 KT 35 MPH 12H 05/0600Z 17.4N 67.1W 35 KT 40 MPH 24H 05/1800Z 18.6N 68.1W 40 KT 45 MPH 36H 06/0600Z 19.7N 68.8W 40 KT 45 MPH 48H 06/1800Z 20.9N 69.2W 40 KT 45 MPH 72H 07/1800Z 23.1N 69.4W 45 KT 50 MPH 96H 08/1800Z 25.3N 68.9W 45 KT 50 MPH 120H 09/1800Z 29.0N 65.0W 50 KT 60 MPH $$ FORECASTER BLAKE

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