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Tropical Storm DALILA Forecast Discussion Number 18

2013-07-04 04:39:10| National Hurricane Center (East Pacific)

Issued at 800 PM PDT WED JUL 03 2013 000 WTPZ44 KNHC 040239 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 PM PDT WED JUL 03 2013 SATELLITE IMAGERY DURING THE PAST FEW HOURS REVEALS THAT THE CLOUD PATTERN OF DALILA IS DETERIORATING FAST. AN SSMI/S MICROWAVE PASS...AROUND 0000 UTC...SHOWED THAT THE LOW-LEVEL CENTER IS REMOVED FROM A SHRINKING AREA OF DEEP CONVECTION. FURTHERMORE... LATEST AVAILABLE SCATTEROMETER DATA SUGGEST THAT THE WINDS COULD BE LOWER THAN INDICATED. HOWEVER...SINCE I INHERITED A 60-KNOT STORM...I WOULD RATHER LOWER THE WINDS GRADUALLY...AND THE INITIAL INTENSITY IS SET AT 50 KNOTS. IT APPEARS THAT DRY AND STABLE AIR IS ALREADY AFFECTING THE CIRCULATION...AND THE SHIPS MODEL FORECASTS INCREASING SHEAR. THE OFFICIAL FORECAST CALLS FOR A GRADUAL WEAKENING...BUT THIS PROCESS COULD OCCUR FASTER THAN FORECAST. DALILA HAS BARELY MOVED DURING THE DAY...TRAPPED TO THE SOUTH OF A STRONG MID-LEVEL RIDGE. THIS PATTERN SHOULD KEEP THE CYCLONE ON A SLOW WEST-SOUTHWESTWARD TO WESTWARD TRACK DURING THE NEXT FEW DAYS UNTIL DISSIPATION. THIS SCENARIO IS CONSISTENT WITH MOST OF THE TRACK MODEL GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 17.6N 108.4W 50 KT 60 MPH 12H 04/1200Z 17.5N 109.0W 45 KT 50 MPH 24H 05/0000Z 17.4N 110.0W 40 KT 45 MPH 36H 05/1200Z 17.5N 111.0W 35 KT 40 MPH 48H 06/0000Z 17.6N 112.2W 30 KT 35 MPH 72H 07/0000Z 18.0N 115.0W 30 KT 35 MPH 96H 08/0000Z 18.5N 117.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 09/0000Z 19.0N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER AVILA

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Tropical Storm DALILA Forecast Discussion Number 17

2013-07-03 22:35:07| National Hurricane Center (East Pacific)

Issued at 200 PM PDT WED JUL 03 2013 000 WTPZ44 KNHC 032034 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 PM PDT WED JUL 03 2013 CLOUD TOPS HAVE BEEN WARMING RECENTLY...AND THE CDO HAS TAKEN ON A PATTERN THAT IS MORE INDICATIVE OF EASTERLY VERTICAL WIND SHEAR. OBJECTIVE DVORAK INTENSITY ESTIMATES HAVE BEEN DECREASING FOR THE PAST SEVERAL HOURS...AND SUBJECTIVE DATA T-NUMBERS HAVE ALSO DECREASED. BASED ON THE DVORAK ESTIMATES...DALILA HAS BEEN DOWNGRADED TO A 60-KT TROPICAL STORM. THERE HAS BEEN VERY LITTLE CHANGE IN THE INTENSITY GUIDANCE. ALTHOUGH THE DYNAMICAL MODELS INDICATE THAT THE INTENSITY COULD FLUCTUATE DURING THE NEXT 48 HOURS...ALL OF THE MODELS GENERALLY FORECAST A SLOW WEAKENING TREND. THE INTENSITY FORECAST HAS BEEN ADJUSTED DOWNWARD A LITTLE TO ACCOUNT FOR THE NEW INITIAL INTENSITY...AND STILL SHOWS DALILA GRADUALLY WEAKENING TO A REMNANT LOW BY THE END OF THE FORECAST PERIOD. ALTHOUGH THE LOW-LEVEL CENTER IS STILL OBSCURED...A COUPLE OF MICROWAVE PASSES SUGGEST THAT IT IS DISPLACED SLIGHTLY TO THE NORTHEAST OF THE CENTER OF THE CDO. THE TROPICAL STORM HAS BEEN DRIFTING SOUTHWESTWARD DURING THE DAY...AND THE INITIAL MOTION ESTIMATE IS 230/3. DALILA IS BEING STEERED BY A LARGE DEEP-LAYER RIDGE TO THE NORTH-NORTHWEST. A TURN TOWARD THE WEST...AND EVENTUALLY THE NORTH-NORTHWEST...IS EXPECTED AS THE RIDGE PROPAGATES EASTWARD. THE MODEL GUIDANCE STILL DOES NOT AGREE ON HOW QUICKLY THIS TURN WILL OCCUR...AND THERE IS A LOT OF SPREAD AT 3-5 DAYS. THE OFFICIAL TRACK FORECAST HAS BEEN SHIFTED A LITTLE TO THE SOUTH...BUT REMAINS NEAR THE FSSE AND GFS MODEL PREDICTIONS. FORECAST POSITIONS AND MAX WINDS INIT 03/2100Z 17.4N 108.1W 60 KT 70 MPH 12H 04/0600Z 17.1N 108.9W 55 KT 65 MPH 24H 04/1800Z 16.8N 109.9W 55 KT 65 MPH 36H 05/0600Z 16.8N 111.0W 55 KT 65 MPH 48H 05/1800Z 16.9N 112.1W 55 KT 65 MPH 72H 06/1800Z 17.6N 114.7W 45 KT 50 MPH 96H 07/1800Z 18.0N 117.0W 35 KT 40 MPH 120H 08/1800Z 18.5N 120.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH/ZELINSKY

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Hurricane DALILA Forecast Discussion Number 16

2013-07-03 16:42:36| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED JUL 03 2013 000 WTPZ44 KNHC 031442 TCDEP4 HURRICANE DALILA DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 AM PDT WED JUL 03 2013 DALILA APPEARS TO HAVE UNDERGONE ANOTHER STRUCTURAL TRANSFORMATION...AND A 0935 UTC MICROWAVE IMAGE FROM TRMM INDICATED THAT THE INNER-CORE HAD BECOME A LITTLE BETTER ORGANIZED. A CONSENSUS OF OBJECTIVE AND SUBJECTIVE DVORAK INTENSITY ESTIMATES AT 1200 UTC IS ABOUT 70 KT...HOWEVER THE CLOUD TOPS HAVE WARMED A LITTLE SINCE THEN...SO THE INITIAL INTENSITY HAS BEEN HELD AT 65 KT. THE INTENSITY GUIDANCE HAS NOT CHANGED MUCH...AND SUGGESTS THAT DALILA WILL REMAIN NEAR HURRICANE INTENSITY FOR THE FIRST 48 HOURS. AFTER THAT...STEADY WEAKENING IS EXPECTED WHILE DALILA MOVES INTO AN AREA OF COLDER WATER AND STRONGER SHEAR...AS INDICATED BY THE SHIPS DIAGNOSTIC OUTPUT. DALILA IS STILL EXPECTED TO BECOME A REMNANT LOW BY THE END OF THE FORECAST PERIOD. THE CENTER OF DALILA REMAINS DIFFICULT TO FIND...HOWEVER EXTRAPOLATING THE POSITION OF THE CENTER OF THE CYCLONE AS INDICATED ON THE AFOREMENTIONED TRMM PASS YIELDS AN ESTIMATED MOTION OF 240/3. DALILA SHOULD CONTINUE TO MOVE SLOWLY TO THE WEST-SOUTHWEST FOR THE NEXT 36 HOURS OR SO...BEFORE TURNING TO THE WEST AND EVENTUALLY WEST-NORTHWEST WHILE THE DEEP-LAYER RIDGE TO ITS NORTH PROPAGATES EASTWARD. THE DYNAMICAL TRACK GUIDANCE STILL VARIES GREATLY ON HOW QUICKLY DALILA WILL TURN TO THE WEST-NORTHWEST. THE OFFICIAL TRACK FORECAST IS VERY NEAR THAT OF THE GFS...WHICH HAS BEEN A GOOD PERFORMER FOR THIS STORM THUS FAR. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 17.8N 108.0W 65 KT 75 MPH 12H 04/0000Z 17.6N 108.5W 65 KT 75 MPH 24H 04/1200Z 17.2N 109.5W 65 KT 75 MPH 36H 05/0000Z 17.1N 110.6W 60 KT 70 MPH 48H 05/1200Z 17.1N 111.7W 60 KT 70 MPH 72H 06/1200Z 17.5N 114.0W 50 KT 60 MPH 96H 07/1200Z 18.5N 116.5W 40 KT 45 MPH 120H 08/1200Z 19.0N 119.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER PASCH/ZELINSKY

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Hurricane DALILA Forecast Discussion Number 15

2013-07-03 10:42:34| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED JUL 03 2013 000 WTPZ44 KNHC 030842 TCDEP4 HURRICANE DALILA DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 AM PDT WED JUL 03 2013 EARLIER MICROWAVE IMAGERY SUGGESTED THAT THE CORE CONVECTION OF DALILA HAD AGAIN BECOME SOMEWHAT DISORGANIZED...POSSIBLY DUE TO SHEAR INDICATED BY CIRRUS CLOUDS MOVING INTO THE CYCLONE FROM THE EAST. HOWEVER...THE CLOUD TOP TEMPERATURES REMAIN PERSISTENTLY NEAR OR COLDER THAN -80C...AND THE SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB HAVE NOT CHANGED DURING THE PAST 12 HOURS. THE INITIAL INTENSITY THUS REMAINS 65 KT...ALTHOUGH IT IS POSSIBLE THAT THIS IS GENEROUS. THE INITIAL MOTION IS AN UNCERTAIN 225/2. THERE IS LITTLE CHANGE IN EITHER THE TRACK FORECAST PHILOSOPHY OR THE MODEL GUIDANCE SINCE THE LAST ADVISORY. A STRONG DEEP-LAYER RIDGE OVER THE WESTERN UNITED STATES SHOULD BUILD SOUTHEASTWARD DURING THE NEXT SEVERAL DAYS AS A TROPICAL DISTURBANCE SOUTH OF EASTERN MEXICO MOVES TOWARD DALILA. THIS EVOLUTION SHOULD CAUSE THE CYCLONE TO MOVE GENERALLY WEST-SOUTHWESTWARD FOR 36 HOURS OR SO...FOLLOWED BY A WESTWARD MOTION. THE GUIDANCE BECOMES QUITE DIVERSE AFTER 72 HOURS...WITH FORECAST TRACKS SPREAD BETWEEN A SOUTHWESTWARD MOTION AND A NORTHWESTWARD MOTION. THIS PORTION OF THE TRACK WILL SHOW A GENERAL WEST-NORTHWESTWARD MOTION NEAR THE CENTER OF THE GUIDANCE ENVELOPE. THE NEW FORECAST TRACK IS SIMILAR TO THE PREVIOUS TRACK. THE ECMWF...UKMET...AND CANADIAN MODELS FORECAST DALILA TO DISSIPATE COMPLETELY DURING THE NEXT 3-5 DAYS...WHILE THE GFS AND NAVGEM MODEL SHOW IT SURVIVING AS A TROPICAL CYCLONE OR LOW PRESSURE AREA FOR 5 DAYS. THE DISSIPATION SCENARIO IS SUPPORTED BY DRY AIR SEEN NEAR THE CYCLONE IN MICROWAVE DATA...WHILE THE SURVIVAL SCENARIO IS SUPPORTED BY WARM SEA SURFACE TEMPERATURES DURING THE FIRST 3 DAYS OF THE NEW FORECAST TRACK. THE INTENSITY FORECAST GOES WITH THE SURVIVAL SCENARIO...CALLING FOR DALILA TO MAINTAIN HURRICANE STRENGTH FOR 24 HOURS WITH GRADUAL WEAKENING THEREAFTER. THE INTENSITY FORECAST HAS BEEN TWEAKED SLIGHTLY TO MATCH THE INTENSITY CONSENSUS FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 18.1N 107.5W 65 KT 75 MPH 12H 03/1800Z 17.8N 107.9W 65 KT 75 MPH 24H 04/0600Z 17.4N 108.7W 65 KT 75 MPH 36H 04/1800Z 17.2N 109.6W 60 KT 70 MPH 48H 05/0600Z 17.2N 110.7W 55 KT 65 MPH 72H 06/0600Z 17.5N 113.0W 50 KT 60 MPH 96H 07/0600Z 18.0N 115.0W 40 KT 45 MPH 120H 08/0600Z 18.5N 117.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER BEVEN

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Hurricane DALILA Forecast Discussion Number 14

2013-07-03 04:40:39| National Hurricane Center (East Pacific)

Issued at 800 PM PDT TUE JUL 02 2013 000 WTPZ44 KNHC 030240 TCDEP4 HURRICANE DALILA DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 PM PDT TUE JUL 02 2013 THE CLOUD PATTERN OF DALILA HAS CHANGED LITTLE IN ORGANIZATION DURING THE LAST SEVERAL HOURS...WITH THE CYCLONE STILL MAINTAINING A SMALL AND FAIRLY SYMMETRIC CDO. A 0016 UTC SSMI/S PASS DID... HOWEVER...SHOW A SLIGHT DEGRADATION OF THE INNER CORE...WITH THE EYEWALL OPEN TO THE EAST. THE MID-LEVEL CENTER ALSO WAS DISPLACED NORTHWEST OF THE LOW-LEVEL CENTER...SUGGESTING THAT SOUTHEASTERLY SHEAR IS STILL AFFECTING THE CYCLONE. THE INITIAL INTENSITY IS KEPT AT 65 KT IN AGREEMENT WITH A TAFB DVORAK INTENSITY ESTIMATE OF T4.0/65 KT. THE STATISTICAL MODEL GUIDANCE SHOWS DALILA CHANGING LITTLE IN STRENGTH DURING THE NEXT 2-3 DAYS...EVEN THOUGH THE HURRICANE SHOULD BE PASSING OVER RELATIVELY WARM WATERS. THE MAIN OBSTACLE TO ANY FURTHER STRENGTHENING IS LIKELY RELATED TO MODERATE EAST- SOUTHEASTERLY TO SOUTHEASTERLY WIND SHEAR FORECAST TO PREVAIL OVER THE CYCLONE. THE ECMWF SHOWS DALILA QUICKLY WEAKENING AS A RESULT OF THE ENTRAINMENT OF A LAYER OF DRY AIR TO THE WEST OF DALILA. IT IS DIFFICULT...HOWEVER...TO IMAGINE THIS SCENARIO...GIVEN THAT THE UPPER-LEVEL FLOW IS FROM THE EAST. THE NHC INTENSITY FORECAST CONTINUES TO LEAN ON THE GFS-BASED MODEL GUIDANCE AND IS NEAR A BLEND OF THE SHIPS/LGEM THROUGH 72 HOURS...AND THEN NEAR THE MULTI-MODEL INTENSITY CONSENSUS AIDS BEYOND THAT TIME. DALILA IS NOT MOVING MUCH. A LONG-TERM AVERAGE OF SATELLITE FIXES YIELDS A HIGHLY UNCERTAIN INITIAL MOTION ESTIMATE OF 270/02. HOWEVER...RECENT MICROWAVE FIXES SUGGEST THAT A WEST-SOUTHWESTWARD TO SOUTHWESTWARD DRIFT MAY HAVE COMMENCED. A MID-LEVEL TROUGH ACROSS NORTHERN MEXICO HAS TEMPORARILY WEAKENED THE SUBTROPICAL RIDGE AND CREATED A WEAK STEERING ENVIRONMENT OVER THE CYCLONE. HOWEVER...THE STRONG HEAT RIDGE OVER THE WESTERN UNITED STATES IS FORECAST TO MOVE SOUTHEASTWARD DURING THE NEXT COUPLE OF DAYS...WHICH SHOULD CAUSE DALILA TO TURN SOUTH OF WEST WITH SOME MINOR INCREASE IN FORWARD SPEED. THE TRACK GUIDANCE REMAINS DIVERSE...WITH THE ECMWF STILL FORECASTING A WEAK CYCLONE MOVING SOUTHWARD AND DISSIPATING. THE GFS CONTINUES TO SHOW A STRONGER SYSTEM MOVING ON A MORE WESTERLY TRACK. THE NEW NHC TRACK FORECAST CONTINUES TO WEIGH THE GFS SOLUTION MORE...AND IS BETWEEN THE PREVIOUS FORECAST AND THE MULTI-MODEL CONSENSUS TVCE THROUGH 72 HOURS...AND CLOSER TO THE GFS LATE IN THE PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 03/0300Z 18.3N 107.3W 65 KT 75 MPH 12H 03/1200Z 18.1N 107.6W 65 KT 75 MPH 24H 04/0000Z 17.7N 108.2W 65 KT 75 MPH 36H 04/1200Z 17.4N 108.9W 65 KT 75 MPH 48H 05/0000Z 17.4N 109.9W 60 KT 70 MPH 72H 06/0000Z 17.6N 111.9W 55 KT 65 MPH 96H 07/0000Z 18.0N 114.0W 40 KT 45 MPH 120H 08/0000Z 18.5N 116.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN

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