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Tropical Storm GABRIELLE Forecast Discussion Number 8

2013-09-10 16:40:02| National Hurricane Center (Atlantic)

Issued at 1100 AM AST TUE SEP 10 2013 000 WTNT42 KNHC 101439 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 1100 AM AST TUE SEP 10 2013 THE CONVECTIVE PATTERN OF GABRIELLE CONTINUES TO FEATURE VERY COLD CLOUD TOPS IN A CDO TYPE FEATURE. MICROWAVE AND GEOSTATIONARY SATELLITE IMAGERY CONTINUE TO SUGGEST THAT THE LOW-LEVEL CENTER IS LOCATED ON THE SOUTHWESTERN SIDE OF THE DEEP CONVECTION...AND THIS STRUCTURE IS CONSISTENT WITH THE 25 KT OR SO OF SOUTHWESTERLY SHEAR ANALYZED OVER THE SYSTEM BY UW-CIMSS. THE INITIAL INTENSITY REMAINS 35 KT IN AGREEMENT WITH THE LATEST DVORAK CLASSIFICATIONS FROM TAFB AND SAB. AN AIR FORCE RESERVE AIRCRAFT WILL INVESTIGATE GABRIELLE THIS AFTERNOON TO PROVIDE MORE DETAILED INFORMATION ON THE EXACT LOCATION AND STRENGTH OF THE CYCLONE. THE ENVIRONMENT WILL REMAIN MARGINAL FOR STRENGTHENING DURING THE NEXT COUPLE OF DAYS...AS GABRIELLE REMAINS OVER SSTS ABOVE 27C WITH MODERATE SOUTHWESTERLY TO WESTERLY VERTICAL SHEAR. THE NHC INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY AND IS CLOSE TO THE CONSENSUS AIDS FOR THE FIRST 48 HOURS. LATE IN THE PERIOD...THE GLOBAL MODELS SHOW LITTLE CHANGE IN INTENSITY DURING AND AFTER EXTRATROPICAL TRANSITION...WHICH SHOULD BE COMPLETE BY 96 HOURS. GABRIELLE SHOULD DISSIPATE OR BE ABSORBED BY DAY 5. THE INITIAL MOTION ESTIMATE IS 360/10...AS THE CYCLONE IS CURRENTLY SITUATED BETWEEN A MID-LEVEL RIDGE TO THE EAST AND A MID/UPPER- LEVEL LOW TO THE WEST. THE FORWARD MOTION OF GABRIELLE WILL SLOW AS THE STEERING FLOW WEAKENS...AND THE CYCLONE SHOULD TURN GRADUALLY TOWARD THE NORTHWEST BY 48 HOURS. LATER IN THE PERIOD...GABRIELLE WILL ACCELERATE NORTHEASTWARD AHEAD OF A DEEP-LAYER TROUGH MOVING INTO EASTERN NORTH AMERICA IN 3-4 DAYS. THE NHC FORECAST IS LARGELY AN UPDATE OF THE PREVIOUS ONE THROUGH 48 HOURS AND THEN TRENDS A LITTLE SLOWER AT DAYS 3 AND 4...LYING BETWEEN THE FASTER ECMWF AND THE SLOWER TVCA MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 30.6N 65.0W 35 KT 40 MPH 12H 11/0000Z 31.9N 64.9W 40 KT 45 MPH 24H 11/1200Z 33.1N 65.2W 45 KT 50 MPH 36H 12/0000Z 34.0N 65.8W 45 KT 50 MPH 48H 12/1200Z 35.2N 66.2W 45 KT 50 MPH 72H 13/1200Z 39.5N 65.0W 45 KT 50 MPH 96H 14/1200Z 49.0N 56.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/1200Z...DISSIPATED $$ FORECASTER BRENNAN

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Tropical Storm HUMBERTO Forecast Discussion Number 8

2013-09-10 16:35:12| National Hurricane Center (Atlantic)

Issued at 1100 AM AST TUE SEP 10 2013 000 WTNT44 KNHC 101434 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 1100 AM AST TUE SEP 10 2013 SATELLITE IMAGES INDICATE THAT HUMBERTO HAS STOPPED INTENSIFYING... AT LEAST FOR THE MOMENT. RECENT MICROWAVE DATA SHOWED THAT THE STORM HAD A SMALL MICROWAVE EYE OVERNIGHT...BUT THAT FEATURE HAS SINCE DISSOLVED AND HAS BEEN REPLACED BY A LARGER BUT BROKEN INNER BAND OF CONVECTION. IN SOME SENSE...THIS SUGGESTS AN EYEWALL REPLACEMENT...EXCEPT THAT HUMBERTO IS STILL A TROPICAL STORM. THE INITIAL INTENSITY IS HELD AT 55 KT BASED ON A CONSENSUS OF SUBJECTIVE AND OBJECTIVE SATELLITE INTENSITY ESTIMATES. HUMBERTO HAS MAINTAINED A MOTION OF 295/8 KT...BUT THE STORM IS EXPECTED TO TURN NORTHWESTWARD LATER TODAY DUE TO A WEAKENING AZORES HIGH TO THE NORTH. TWO DEEP-LAYERED LOWS ARE FORECAST TO DEVELOP NORTH OF THE CANARY ISLANDS AND OVER THE CENTRAL ATLANTIC OVER THE NEXT COUPLE OF DAYS. THESE FEATURES...ALONG WITH A RIDGE EXTENDING WESTWARD FROM NORTH AFRICA...SHOULD STEER HUMBERTO NORTHWARD IN ABOUT 36 HOURS. HIGH PRESSURE IS FORECAST TO REBUILD NORTH OF HUMBERTO BY DAYS 4 AND 5...WHICH SHOULD TURN THE CYCLONE WESTWARD BY THE END OF THE FORECAST PERIOD. CONFIDENCE IN THIS FORECAST IS HIGH SINCE THERE IS VERY LITTLE SPREAD IN THE TRACK GUIDANCE...AND NO SIGNIFICANT CHANGES TO THE OFFICIAL FORECAST WERE REQUIRED ON THIS CYCLE. ONCE THE INNER CORE OF HUMBERTO REORGANIZES...THERE IS A WINDOW OF ABOUT 36 TO 48 HOURS FOR ADDITIONAL STRENGTHENING BEFORE VERTICAL SHEAR INCREASES AND THE STORM REACHES A MORE HOSTILE THERMODYNAMIC ENVIRONMENT. THE OFFICIAL FORECAST CONTINUES TO SHOW HUMBERTO REACHING HURRICANE STRENGTH LATER TODAY...BUT THE FORECAST PEAK INTENSITY IN A DAY OR TWO HAS BEEN ADJUSTED DOWNWARD JUST A BIT BASED ON THE LATEST INTENSITY GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 14.6N 27.7W 55 KT 65 MPH 12H 11/0000Z 15.3N 28.5W 65 KT 75 MPH 24H 11/1200Z 16.6N 29.2W 70 KT 80 MPH 36H 12/0000Z 18.5N 29.5W 80 KT 90 MPH 48H 12/1200Z 20.5N 29.8W 80 KT 90 MPH 72H 13/1200Z 23.5N 31.0W 70 KT 80 MPH 96H 14/1200Z 24.5N 34.5W 55 KT 65 MPH 120H 15/1200Z 25.0N 39.5W 45 KT 50 MPH $$ FORECASTER BERG

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Tropical Storm HUMBERTO Forecast Discussion Number 7

2013-09-10 10:46:29| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE SEP 10 2013 000 WTNT44 KNHC 100846 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 500 AM AST TUE SEP 10 2013 HUMBERTO CONTINUES TO STEADILY STRENGTHEN. SATELLITE IMAGES INDICATE THAT THE ASSOCIATED BANDING FEATURES HAVE BECOME BETTER ORGANIZED AND MORE SYMMETRIC AROUND THE CENTER...INDICATING THAT VERTICAL WIND SHEAR IS DECREASING OVER THE CYCLONE. DVORAK CLASSIFICATIONS FROM TAFB AND SAB WERE BOTH T3.5 AND UW-CIMSS ADT VALUES ARE ABOUT THE SAME. BASED ON THESE ESTIMATES...THE INITIAL WIND SPEED IS INCREASED TO 55 KT. THE TROPICAL STORM IS GRADUALLY TURNING TO THE RIGHT...AND THE LATEST INITIAL MOTION ESTIMATE IS 295/8. A TURN TO THE NORTHWEST IS EXPECTED TODAY...FOLLOWED BY A NORTHWARD MOTION ON WEDNESDAY. THIS ABRUPT CHANGE IN THE FORECAST STORM MOTION IS DUE TO A BREAK DOWN OF THE SUBTROPICAL RIDGE THAT WILL BE CAUSED BY A MID- TO UPPER-LEVEL LOW MOVING SOUTHWARD OVER THE CENTRAL ATLANTIC AND ANOTHER LOW BETWEEN THE CANARY ISLANDS AND THE AZORES. A SHARP WESTWARD TURN IS FORECAST TO OCCUR IN ABOUT 4 DAYS WHEN THE RIDGE BECOMES RE-ESTABLISHED. THE NHC TRACK FORECAST IS IN FAIR AGREEMENT GIVEN THE PRONOUNCED HEADING CHANGES...AND THE LATEST OFFICIAL FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS TVCA. THE INTENSIFICATION TREND IS EXPECTED TO CONTINUE FOR ANOTHER 36 HOURS WHILE HUMBERTO REMAINS OVER WARM WATER AND WITHIN AN ENVIRONMENT OF LOW WIND SHEAR AND HIGH MID-LEVEL MOISTURE. AFTER THAT TIME...THE GLOBAL MODELS SHOW DRIER AIR AND SOUTHERLY TO SOUTHWESTERLY SHEAR AFFECTING HUMBERTO. THESE UNFAVORABLE ATMOSPHERIC CONDITIONS COMBINED WITH COOLER SSTS SHOULD CAUSE THE SYSTEM TO BEGIN WEAKENING IN A COUPLE OF DAYS. THE NHC INTENSITY FORECAST IS NEAR THE HIGH END OF THE MODEL GUIDANCE IN THE SHORT TERM AND IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 14.4N 26.6W 55 KT 65 MPH 12H 10/1800Z 15.0N 27.5W 65 KT 75 MPH 24H 11/0600Z 16.2N 28.3W 75 KT 85 MPH 36H 11/1800Z 17.9N 28.8W 85 KT 100 MPH 48H 12/0600Z 20.0N 29.1W 85 KT 100 MPH 72H 13/0600Z 23.7N 30.0W 75 KT 85 MPH 96H 14/0600Z 25.5N 32.5W 55 KT 65 MPH 120H 15/0600Z 26.0N 36.5W 45 KT 50 MPH $$ FORECASTER CANGIALOSI

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Tropical Storm GABRIELLE Forecast Discussion Number 7

2013-09-10 10:46:04| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE SEP 10 2013 000 WTNT42 KNHC 100845 TCDAT2 TROPICAL STORM GABRIELLE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013 500 AM AST TUE SEP 10 2013 DURING THE PAST 12 HOURS...INFRARED SATELLITE IMAGERY INDICATES DEEP CONVECTION HAS DEVELOPED AND PERSISTED OVER AND TO THE EAST OF THE WELL-DEFINED LOW-LEVEL CIRCULATION CENTER ASSOCIATED WITH THE REMNANTS OF GABRIELLE. IN ADDITION...AN EARLIER ASCAT OVERPASS CONTAINED SOME 34- TO 36-KT WIND VECTORS TO THE SOUTH OF THE CENTER AND OBSERVATIONS FROM NOAA BUOY 41049 LOCATED MORE THAN 100 NMI SOUTHEAST OF THE CENTER HAVE BEEN STEADILY INCREASING TO AT LEAST 31 KT OUTSIDE OF CONVECTION. BASED ON THE ABOVE DATA...ADVISORIES HAVE BEEN RE-INITIATED ON TROPICAL STORM GABRIELLE. AN AIR FORCE RESERVE AIRCRAFT IS SCHEDULED TO RECONNOITER THE CYCLONE THIS AFTERNOON TO PROVIDE MORE DETAILED INFORMATION ON THE EXACT LOCATION AND STRENGTH OF GABRIELLE. THE INITIAL MOTION ESTIMATE IS 360/10 KT...WHICH IS BASED MAINLY ON LIMITED MICROWAVE FIXES. THE NHC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT ON GABRIELLE MOVING NORTHWARD TO NORTH-NORTHWESTWARD AND SLOWING DOWN DURING THE NEXT 36 TO 48 HOURS AS THE CYCLONE MOVES AROUND THE EASTERN PERIPHERY OF A RETROGRADING MID-/UPPER-LEVEL LOW CURRENTLY LOCATED JUST NORTH OF THE BAHAMAS. ON THE FORECAST TRACK...GABRIELLE IS EXPECTED TO PASS OVER OR NEAR BERMUDA IN ABOUT 24 HOURS. BY 72 HOURS...GABRIELLE IS FORECAST TO BEGIN TO LIFT OUT AND ACCELERATE NORTHWARD AND THEN NORTHEASTWARD AHEAD OF A STRONG MID-TROPOSPHERIC TROUGH AND FRONTAL SYSTEM THAT IS FORECAST TO MOVE OFF OF THE U.S. EAST COAST BY 96 HOURS. THE OFFICIAL FORECAST TRACK IS CLOSE TO THE MULTI-MODEL CONSENSUS TVCA. GABRIELLE IS EXPECTED TO REMAIN IN A MODERATE SHEAR ENVIRONMENT BUT OVER 28-29C SSTS FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD ALLOW FOR SOME ADDITONAL STRENGTHENING TO OCCUR. THE INTENSITY IS EXPECTED TO LEVEL OFF BY 48 HOURS AS SOUTHWESTERLY VERTICAL WIND SHEAR BEGINS TO GRADUALLY INCREASE AHEAD OF THE AFOREMENTIONED APPROACHING FRONTAL SYSTEM. AT 72 HOURS AND BEYOND...GABRIELLE WILL BE MOVING OVER SUB-25C SSTS AND THE CYCLONE IS FORECAST TO BECOME A POST-TROPICAL/EXTRATROPICAL LOW BY 96 HOURS WHEN WATER TEMPERATURES WILL BE LESS THAN 20C. THE NHC INTENSITY FORECAST IS CLOSE TO THE CONSENSUS MODEL ICON. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 29.6N 65.0W 35 KT 40 MPH 12H 10/1800Z 31.1N 65.0W 40 KT 45 MPH 24H 11/0600Z 32.7N 65.2W 45 KT 50 MPH 36H 11/1800Z 33.7N 65.7W 45 KT 50 MPH 48H 12/0600Z 34.5N 66.3W 45 KT 50 MPH 72H 13/0600Z 37.7N 65.9W 45 KT 50 MPH 96H 14/0600Z 46.8N 58.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 15/0600Z 56.5N 41.9W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ FORECASTER STEWART

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Tropical Storm HUMBERTO Forecast Discussion Number 6

2013-09-10 04:46:59| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON SEP 09 2013 000 WTNT44 KNHC 100246 TCDAT4 TROPICAL STORM HUMBERTO DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013 1100 PM AST MON SEP 09 2013 RECENT MICROWAVE IMAGES AND SCATTEROMETER DATA INDICATE THAT THE CENTER OF HUMBERTO REMAINS NEAR THE NORTHEASTERN EDGE OF A LARGE MASS OF DEEP CONVECTION. THIS SUGGESTS THAT SOME EAST- NORTHEASTERLY SHEAR REMAINS OVER THE CYCLONE...ALTHOUGH RECENT SATELLITE PICTURES SHOW THAT CIRRUS OUTFLOW IS BEGINNING TO EXPAND OUTWARD OVER THE EASTERN PORTION OF THE STORM. THE ASCAT DATA INDICATE THAT THE MAXIMUM WINDS HAVE INCREASED TO AROUND 50 KT...AND THAT THE AREA OF TROPICAL STORM FORCE WINDS HAS ALSO EXPANDED SINCE THIS MORNING. SATELLITE CENTER FIXES OVER THE PAST 12 HOURS SUGGEST THAT HUMBERTO IS MOVING A LITTLE SLOWER THAN EARLIER TODAY...WITH A MOTION OF 285/9 KT. THE MID-LEVEL RIDGE TO THE NORTH OF THE STORM IS EXPECTED TO WEAKEN VERY SOON AS A COUPLE OF MID- TO UPPER-LEVEL LOWS MOVE SOUTHWARD OVER THE EASTERN ATLANTIC. THIS SHOULD CAUSE HUMBERTO TO TURN NORTH-NORTHWESTWARD IN 24 TO 36 HOURS AND A GENERAL NORTHWARD MOTION IS FORECAST TO THEN CONTINUE THROUGH 72 HOURS. AFTER THAT TIME...THE GLOBAL MODELS INDICATE THAT THE RIDGE WILL REBUILD TO THE NORTHWEST OF THE AZORES AND THIS SHOULD TURN HUMBERTO BACK TO THE WEST-NORTHWEST BY THE END OF THE FORECAST PERIOD. THE VERTICAL SHEAR CURRENTLY OVER HUMBERTO SHOULD DECREASE SOON...AND THIS SHOULD ALLOW FOR STEADY STRENGTHENING DURING THE NEXT COUPLE OF DAYS WHILE THE CYCLONE REMAINS OVER WARM WATER. THE MAJORITY OF THE INTENSITY GUIDANCE BRINGS HUMBERTO TO HURRICANE STRENGTH WITHIN 24 HOURS...AND SO DOES THE OFFICIAL FORECAST. THE NHC INTENSITY FORECAST SHOWS A SLIGHTLY HIGHER PEAK INTENSITY THAN THE PREVIOUS ADVISORY...BUT STILL IT IS NOT AS AGGRESSIVE AS THE SHIPS GUIDANCE. AFTER 72 HOURS...THE SHEAR IS FORECAST TO BECOME QUITE STRONG OUT OF THE SOUTHWEST...AND THIS IS EXPECTED TO INDUCE SIGNIFICANT WEAKENING. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 13.9N 25.9W 50 KT 60 MPH 12H 10/1200Z 14.4N 27.1W 60 KT 70 MPH 24H 11/0000Z 15.4N 28.1W 70 KT 80 MPH 36H 11/1200Z 16.9N 28.7W 80 KT 90 MPH 48H 12/0000Z 19.1N 29.1W 85 KT 100 MPH 72H 13/0000Z 23.0N 30.0W 75 KT 85 MPH 96H 14/0000Z 25.2N 32.3W 55 KT 65 MPH 120H 15/0000Z 26.0N 36.0W 45 KT 50 MPH $$ FORECASTER BROWN

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