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Hurricane DALILA Forecast Discussion Number 13

2013-07-02 22:32:36| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE JUL 02 2013 000 WTPZ44 KNHC 022032 TCDEP4 HURRICANE DALILA DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 PM PDT TUE JUL 02 2013 A COUPLE OF MICROWAVE IMAGES...RECEIVED SHORTLY AFTER THE RELEASE OF THE 1500 UTC ADVISORY...SHOWED THAT THE INNER-CORE STRUCTURE OF DALILA BECAME SUBSTANTIALLY BETTER DEFINED DURING THE MORNING HOURS. IN PARTICULAR...1335 UTC WINDSAT MICROWAVE IMAGE SHOWED THAT THAT AN EYE HAD DEVELOPED. THAT PASS ALSO INDICATED THAT THE CENTER OF DALILA WAS NORTH OF THE PREVIOUSLY ESTIMATED POSITION. A RAGGED EYE-LIKE FEATURE IS STILL PRESENT IN VISIBLE IMAGERY AND THE OVERALL CLOUD PATTERN HAS BECOME FAIRLY SYMMETRIC. THE INITIAL INTENSITY IS SET TO 65 KT...BASED ON A BLEND OF MICROWAVE-ADJUSTED OBJECTIVE DVORAK INTENSITY ESTIMATES FROM UW-CIMSS AND SUBJECTIVE DVORAK ESTIMATES FROM TAFB AND SAB. THERE HAS BEEN A LARGE UPWARD SHIFT IN THE STATISTICAL AND DYNAMICAL INTENSITY GUIDANCE. THE OFFICIAL INTENSITY FORECAST HAS BEEN ADJUSTED UPWARD...ALTHOUGH IT NOW LIES ON THE LOWER END OF THE GUIDANCE RANGE. DALILA IS STILL FORECAST TO BECOME A REMNANT LOW BY 120 HOURS AS IT MOVES INTO A DRIER ENVIRONMENT AND OVER COOLER WATERS. ALTHOUGH THE CENTER HAS BEEN EASIER TO LOCATE...THE TROPICAL CYCLONE IS STILL MOVING VERY SLOWLY AND THE INITIAL MOTION IS RATHER UNCERTAIN. IN THE SHORT RANGE...A DEEP-LAYER RIDGE LOCATED TO THE NORTH OF DALILA IS STILL EXPECTED TO IMPART A TURN TOWARD THE WEST-SOUTHWEST WITHIN THE NEXT 24 HOURS. THERE REMAINS A VERY LARGE SPREAD IN THE GUIDANCE AFTER THAT...AND THE GFS AND ECMWF HAVE NOT COME INTO BETTER AGREEMENT. THE GFS STILL SHOWS A GENERALLY WESTWARD-MOVING STRONG CYCLONE...WHILE THE ECMWF FORECASTS A SOUTHWARD-MOVING WEAK LOW. GIVEN THE CURRENT STATE OF DALILA...MORE CREDENCE IS BEING GIVEN TO THE FORMER SCENARIO. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 18.4N 107.2W 65 KT 75 MPH 12H 03/0600Z 18.3N 107.5W 70 KT 80 MPH 24H 03/1800Z 18.0N 108.1W 65 KT 75 MPH 36H 04/0600Z 17.7N 108.9W 65 KT 75 MPH 48H 04/1800Z 17.5N 109.8W 60 KT 70 MPH 72H 05/1800Z 17.5N 111.5W 60 KT 70 MPH 96H 06/1800Z 18.0N 113.5W 40 KT 45 MPH 120H 07/1800Z 18.5N 116.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH/ZELINSKY

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Hurricane DALILA Forecast Discussion Number 12

2013-07-02 20:04:57| National Hurricane Center (East Pacific)

Issued at 1100 AM PDT TUE JUL 02 2013 000 WTPZ44 KNHC 021804 TCDEP4 HURRICANE DALILA SPECIAL DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 1100 AM PDT TUE JUL 02 2013 THIS IS A SPECIAL ADVISORY TO REVISE THE INTENSITY OF DALILA. A COUPLE OF MICROWAVE PASSES INDICATED A LOW-LEVEL EYE...AND A FAINT EYE IS SEEN IN HIGH-RESOLUTION VISIBLE SATELLITE IMAGES. BASED ON THESE IMAGES...THE SYSTEM IS UPGRADED TO A HURRICANE. BASED ON THE NUMERICAL INTENSITY GUIDANCE...NOT MUCH ADDITIONAL STRENGTHENING IS ANTICIPATED...AND THE SYSTEM SHOULD BEGIN WEAKENING IN A DAY OR SO AS IT INTERACTS WITH DRIER AIR AND THE DEVELOPING CYCLONIC CIRCULATION TO ITS EAST. THE CENTER POSITION IS SOMEWHAT TO THE NORTH OF THE PREVIOUSLY ESTIMATED TRACK...SO THE FORECAST TRACK IS ADJUSTED NORTHWARD A LITTLE. OTHERWISE THERE IS NO CHANGE TO THE TRACK FORECAST REASONING FROM THE PREVIOUS PACKAGE. FORECAST POSITIONS AND MAX WINDS INIT 02/1800Z 18.3N 107.1W 65 KT 75 MPH 12H 03/0000Z 18.2N 107.3W 65 KT 75 MPH 24H 03/1200Z 18.0N 107.7W 60 KT 70 MPH 36H 04/0000Z 17.8N 108.4W 55 KT 65 MPH 48H 04/1200Z 17.6N 109.3W 50 KT 60 MPH 72H 05/1200Z 17.0N 110.8W 40 KT 45 MPH 96H 06/1200Z 16.5N 112.5W 30 KT 35 MPH 120H 07/1200Z 16.5N 115.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH/ZELINSKY

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Tropical Storm DALILA Forecast Discussion Number 11

2013-07-02 16:33:15| National Hurricane Center (East Pacific)

Issued at 800 AM PDT TUE JUL 02 2013 000 WTPZ44 KNHC 021432 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 AM PDT TUE JUL 02 2013 THE CENTER OF DALILA IS HIDDEN BENEATH A CENTRAL DENSE OVERCAST AND HAS BEEN VERY DIFFICULT TO LOCATE DURING THE PAST 6 HOURS. A 0319 UTC SSM/I IMAGE SHOWED THAT THE CENTER WAS DISPLACED NEARLY HALF A DEGREE SOUTH OF THE MAIN AREA OF CONVECTION...HOWEVER NO MICROWAVE IMAGES OF THE CENTER HAVE BEEN AVAILABLE SINCE THAT TIME. THE INITIAL MOTION IS AN UNCERTAIN 270/2. A SLOW MOTION IS EXPECTED TO CONTINUE AS DALILA REMAINS EMBEDDED WITHIN WEAK STEERING FLOW. THE GFS AND ECMWF FORECASTS SUGGEST THAT A DEEP-LAYER RIDGE LOCATED OVER THE SOUTHERN UNITED STATES IS BUILDING TOWARD THE NORTHWEST OF DALILA. THIS WILL LIKELY CAUSE THE TROPICAL CYCLONE TO TURN SLOWLY TOWARD THE WEST-SOUTHWEST. THE SPREAD AMONG THE DYNAMICAL MODELS REMAINS HIGH AFTER 48 HOURS. THE ECMWF FORECASTS THAT A LAYER OF MID- TO UPPER-LEVEL DRY AIR WILL QUICKLY WEAKEN DALILA...AND THE LOW-LEVEL REMNANTS WILL MOVE ALMOST DUE SOUTH. ON THE OTHER HAND...THE GFS FORECASTS THAT THE DRY AIR WILL NOT ENTRAIN INTO THE CENTER OF DALILA...AND A DEEPER VORTEX WILL TRACK WESTWARD AFTER 48 HOURS. IT IS POSSIBLE...HOWEVER...THAT CONVECTIVE FEEDBACK PROCESSES ARE ARTIFICIALLY MOISTENING THE NEAR-STORM ENVIRONMENT IN THE GFS. THE NEW OFFICIAL TRACK FORECAST HAS BEEN SHIFTED SOUTHWARD...A LITTLE CLOSER TO THE ECMWF FORECAST...AND IS ROUGHLY A CONSENSUS OF THE GFS AND ECMWF SOLUTIONS. THE INITIAL INTENSITY REMAINS 55 KT...BASED ON DVORAK CURRENT INTENSITY NUMBERS OF 3.5 FROM TAFB AND SAB. MOST OF THE INTENSITY GUIDANCE SUGGESTS THAT DALILA WILL GRADUALLY WEAKEN DURING THE NEXT SEVERAL DAYS DUE TO CONTINUED MODERATE SOUTHEASTERLY WIND SHEAR. MOST OF THE DYNAMICAL MODELS ALSO SUGGEST THAT THE ENTRAINMENT OF DRY AIR WILL CONTRIBUTE TO THE WEAKENING. THE OFFICIAL FORECAST IS VERY CLOSE TO THE PREVIOUS NHC FORECAST...AND NOW CALLS FOR DALILA TO BECOME A REMNANT LOW BY 120 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 17.7N 106.9W 55 KT 65 MPH 12H 03/0000Z 17.6N 107.3W 55 KT 65 MPH 24H 03/1200Z 17.4N 107.7W 50 KT 60 MPH 36H 04/0000Z 17.2N 108.4W 50 KT 60 MPH 48H 04/1200Z 17.0N 109.3W 50 KT 60 MPH 72H 05/1200Z 16.7N 110.8W 40 KT 45 MPH 96H 06/1200Z 16.5N 112.5W 30 KT 35 MPH 120H 07/1200Z 16.5N 115.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH/ZELINSKY

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Tropical Storm DALILA Forecast Discussion Number 10

2013-07-02 10:40:24| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE JUL 02 2013 000 WTPZ44 KNHC 020840 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 AM PDT TUE JUL 02 2013 MICROWAVE SATELLITE IMAGERY BETWEEN 0000-0400 UTC INDICATES THAT DALILA HAS LOST ORGANIZATION...POSSIBLY DUE TO A COMBINATION OF MODERATE SOUTHEASTERLY VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. THE CONVECTIVE BANDING AROUND THE CENTER HAS DECREASED...WITH THE CENTER NOW TO THE SOUTH OF THE MAIN CONVECTIVE MASS. SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB ARE 55 KT...AND USING THIS ALONG WITH THE DECREASED ORGANIZATION THE INITIAL INTENSITY IS REDUCED TO 55 KT. THE MICROWAVE IMAGERY SHOWS THAT THE CENTER IS SOUTHEAST OF THE PREVIOUS ADVISORY POSITION...WHICH REQUIRES A RE-LOCATION FOR THIS ADVISORY. THE INITIAL MOTION IS A RATHER UNCERTAIN 270/4. DALILA IS IN AN AREA OF WEAK STEERING CURRENT BETWEEN A MID-LEVEL RIDGE TO ITS NORTH...AN UPPER-LEVEL ANTICYCLONE TO ITS EAST...AND A LARGE AREA OF DISTURBED WEATHER TO ITS SOUTHEAST. THE LATTER DISTURBANCE IS FORECAST TO MOVE TOWARD DALILA DURING THE NEXT SEVERAL DAYS. THE TRACK GUIDANCE MODELS SHOW A SIGNIFICANT SPREAD...MAKING THIS A LOW-CONFIDENCE FORECAST. THE NAVGEM...GFDL...AND GFDN FORECAST THE STORM TO MOVED NORTHWESTWARD WEST OF BAJA CALIFORNIA. THE ECMWF AND UKMET FORECAST A SOUTHWESTWARD MOTION DUE TO INTERACTION WITH THE APPROACHING DISTURBANCE. THE GFS AND THE HWRF FORECAST A SLOW WESTWARD TO WEST-SOUTHWESTWARD MOTION...AND THIS IS THE BASIS FOR THE CURRENT FORECAST. THE NEW FORECAST TRACK IS SOUTH OF AND SLOWER THAN THE PREVIOUS TRACK BASED ON THE CURRENT LOCATION AND MOTION. THE NEW FORECAST TRACK COMPLICATES THE INTENSITY FORECAST. ON ONE SIDE...THE SLOWER AND MORE SOUTHERLY TRACK WOULD KEEP THE CYCLONE OVER WARMER SEA SURFACE TEMPERATURES THAN PREVIOUSLY FORECAST. ON THE OTHER SIDE...THE ECMWF..UKMET...AND CANADIAN MODELS ALL FORECAST DALILA TO DISSIPATE BEFORE 120 HOURS DUE TO INTERACTION WITH THE DISTURBANCE. THE INTENSITY FORECAST COMPROMISES BETWEEN THESE POSSIBILITIES...SHOWING LITTLE CHANGE IN STRENGTH FOR 36-48 HOURS FOLLWED BY A GRADUAL WEAKENING AS THE NEW DISTURBANCE GETS CLOSER. THE NEW INTENSITY FORECAST IS WEAKER THAN THE PREVIOUS FORECAST AND IS IN BEST AGREEMENT WITH THE INTENSITY CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 17.7N 106.8W 55 KT 65 MPH 12H 02/1800Z 17.7N 107.2W 55 KT 65 MPH 24H 03/0600Z 17.7N 107.6W 55 KT 65 MPH 36H 03/1800Z 17.5N 108.2W 55 KT 65 MPH 48H 04/0600Z 17.2N 109.0W 50 KT 60 MPH 72H 05/0600Z 17.0N 110.5W 45 KT 50 MPH 96H 06/0600Z 17.0N 112.5W 35 KT 40 MPH 120H 07/0600Z 17.0N 115.0W 25 KT 30 MPH $$ FORECASTER BEVEN

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Tropical Storm DALILA Forecast Discussion Number 9

2013-07-02 04:46:22| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON JUL 01 2013 000 WTPZ44 KNHC 020245 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 PM PDT MON JUL 01 2013 THE CONVECTIVE BANDING PATTERN ASSOCIATED WITH DALILA HAS GRADUALLY MORPHED INTO A SMALL CDO FEATURE OVER THE PAST 6 HOURS...WITH CLOUD TOPS OF -80C AND COLDER ALMOST COMPLETELY ENCIRCLING THE CENTER. A 01/1801 UTC TRMM OVERPASS THAT CAME IN AFTER THE PREVIOUS ADVISORY ALSO REVEALED A CLOSED 10-15 NMI DIAMETER MID-LEVEL EYE. SATELLITE INTENSITY ESTIMATES FROM TAFB REMAIN AT T3.5/55 KT...BUT THE DATA-T NUMBER FROM TAFB WAS 4.0/65 KT. A RECENT CIRA INTENSITY ESTIMATE OF 62 KT...ALONG WITH THE TRMM MICROWAVE EYE FEATURE...JUSTIFIES INCREASING THE INITIAL INTENSITY TO 60 KT. ALTHOUGH DALILA HAS BEEN INCREASING AT THE RATE OF ONE T-NUMBER PER DAY OR 20 KT EVERY 24 HOURS...THAT INTENSIFICATION TREND IS NOT EXPECTED TO LAST MUCH LONGER. THE VERTICAL SHEAR ACROSS DALILA IS FORECAST TO REMAIN MODEST AT 12-15 KT FOR ANOTHER 24 HOURS...WHICH IS EXPECTED TO OFFSET THE FAVORABLE OCEANIC CONDITIONS OF 27-28C SSTS. NOW THAT DALILA HAS SLOWED DOWN MARKEDLY...COLD UPWELLING BENEATH THE CYCLONE IS ALSO EXPECTED TO BECOME A FACTOR SINCE UPPER-OCEAN HEAT CONTENT VALUES ARE QUITE LOW AT ONLY 3-5 UNITS. EVEN THOUGH THE SHEAR IS FORECAST TO DECREASE TO 5 KT OR SO AFTER 24 HOURS...COOLER WATERS AND DRIER MID-LEVEL AIR ARE EXPECTED TO HINDER THE DEVELOPMENT PROCESS. AS A RESULT...THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND IS A BLEND OF THE SHIPS...LGEM...AND FSSE INTENSITY MODELS. VISIBLE AND MICROWAVE SATELLITE FIXES SUGGEST THAT DALILA HAS SLOWED DOWN CONSIDERABLY AS EXPECTED...AND THE INITIAL MOTION ESTIMATE IS NOW 290/05 KT. THE EXTENSIVE MID-LEVEL RIDGE TO THE NORTH OF DALILA IS EXPECTED TO REMAIN INTACT THROUGH THE 5-DAY FORECAST PERIOD AND KEEP THE CYCLONE MOVING IN A GENERAL WESTWARD DIRECTION. BY 48 HOURS...HOWEVER...THE GFS AND THE ECMWF MODELS INDICATE THAT A SOUTHWESTWARD MOTION COULD OCCUR DUE TO SOME BINARY INTERACTION WITH THE DEVELOPING LARGE DISTURBANCE CURRENTLY LOCATED TO THE EAST OVER THE GULF OF TEHUANTEPEC. GIVEN THE UNCERTAINTY IN THE DEVELOPMENT OF AND INFLUENCE BY THE LATTER FEATURE...BOTH THE REASONING AND THE FORECAST TRACK REMAIN BASICALLY UNCHANGED FROM THE PREVIOUS ADVISORY. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 18.2N 106.9W 60 KT 70 MPH 12H 02/1200Z 18.3N 107.4W 65 KT 75 MPH 24H 03/0000Z 18.4N 108.1W 65 KT 75 MPH 36H 03/1200Z 18.4N 108.7W 60 KT 70 MPH 48H 04/0000Z 18.3N 109.3W 55 KT 65 MPH 72H 05/0000Z 18.3N 110.5W 50 KT 60 MPH 96H 06/0000Z 18.4N 112.8W 45 KT 50 MPH 120H 07/0000Z 18.5N 115.8W 35 KT 40 MPH $$ FORECASTER STEWART

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