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Tropical Storm DALILA Forecast Discussion Number 8

2013-07-01 22:48:58| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON JUL 01 2013 000 WTPZ44 KNHC 012048 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 PM PDT MON JUL 01 2013 THE INNER CORE OF DALILA HAS BECOME A LITTLE BETTER ORGANIZED DURING THE PAST FEW HOURS. DVORAK INTENSITY ESTIMATES FROM TAFB...SAB... AND UW-CIMSS HAVE CONVERGED TO A CONSENSUS T-NUMBER OF 3.5...SO THE INITIAL INTENSITY HAS BEEN RAISED TO 55 KT. ALTHOUGH DALILA IS LOCATED IN A SYNOPTIC ENVIRONMENT CONSISTING OF VERY WARM SEA SURFACE TEMPERATURES AND FAIRLY LOW VERTICAL WIND SHEAR...A PRONOUNCED DRY SLOT HAS DEVELOPED IN THE SOUTHEASTERN QUADRANT OF THE STORM WHICH SUGGESTS THAT DRY AIR MAY BE ENTRAINING INTO THE CIRCULATION. MOST OF THE INTENSITY GUIDANCE NOW FORECASTS DALILA TO BECOME A HURRICANE WITHIN THE NEXT 24 HOURS. HOWEVER...THE SPREAD AMONG THE MODELS IS HIGH...ESPECIALLY REGARDING HOW QUICKLY THE DRY AIR AND DECREASING SEA SURFACE TEMPERATURES WILL CAUSE THE CYCLONE TO WEAKEN IN THE 3 TO 5 DAY TIME PERIOD. THE OFFICIAL FORECAST HAS NOT CHANGED SUBSTANTIALLY FROM THE PREVIOUS FORECAST...AND NOW LIES VERY NEAR THE INTENSITY CONSENSUS THROUGH THE ENTIRE FORECAST. THE CENTER OF DALILA HAS BEEN OBSCURED BY A CENTRAL DENSE OVERCAST FEATURE. MICROWAVE-BASED CENTER FIXES SUGGEST THAT THE CYCLONE HAS BEGUN TO TURN AWAY FROM THE MEXICAN COAST...AND THE INITIAL MOTION IS 295/6. WHILE THE REASONING BEHIND THE TRACK FORECAST IS UNCHANGED...THE SPREAD IN THE TRACK GUIDANCE REMAINS VERY HIGH. THE ECMWF FORECASTS A NEARLY DUE SOUTH TRACK...WHILE THE GFS FORECASTS A GENERALLY WESTWARD TRACK THROUGH 120 HOURS. THESE DISCREPANCIES APPEAR TO BE RELATED TO THE STRENGTH AND DEPTH OF THE CYCLONE VORTEX. THE OFFICIAL FORECAST LEANS TOWARD THE GFS SOLUTION WHICH HAS A STRONGER VORTEX...MORE IN LINE WITH THE NHC INTENSITY FORECAST. GIVEN THE UNCERTAINTY IN THE INTENSITY FORECAST...THE DEGREE OF UNCERTAINTY IN THE TRACK FORECAST IS ALSO VERY HIGH. SINCE DALILA HAS BEGUN TO MOVE AWAY FROM MEXICO...THE TROPICAL STORM WATCHES AND WARNINGS ALONG THE COAST OF THAT COUNTRY HAVE BEEN DISCONTINUED. HOWEVER...THE OUTER RAINBANDS OF THE TROPICAL CYCLONE WILL LIKELY CONTINUE TO IMPACT THE SOUTHWEST COAST OF MEXICO THROUGH TONIGHT. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 17.9N 106.5W 55 KT 65 MPH 12H 02/0600Z 18.2N 107.2W 65 KT 75 MPH 24H 02/1800Z 18.4N 107.8W 65 KT 75 MPH 36H 03/0600Z 18.5N 108.5W 60 KT 70 MPH 48H 03/1800Z 18.5N 109.1W 55 KT 65 MPH 72H 04/1800Z 18.5N 110.0W 50 KT 60 MPH 96H 05/1800Z 18.5N 112.0W 45 KT 50 MPH 120H 06/1800Z 18.5N 115.0W 35 KT 40 MPH $$ FORECASTER PASCH/ZELINSKY

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Tropical Storm DALILA Forecast Discussion Number 6

2013-07-01 10:34:57| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON JUL 01 2013 000 WTPZ44 KNHC 010834 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 AM PDT MON JUL 01 2013 THE CLOUD PATTERN HAS NOT BECOME ANY BETTER ORGANIZED DURING THE PAST FEW FEW HOURS AS INDICATED BY IR IMAGERY. THE OUTFLOW IS LIMITED TO THE WESTERN SEMICIRCLE AND THERE ARE NO WELL DEFINED BANDING FEATURES. A BLEND OF T-NUMBERS FROM BOTH TAFB AND SAB SUPPORTS KEEPING THE INITIAL INTENSITY AT 40 KNOTS. DALILA STILL HAS AN OPPORTUNITY TO STRENGTHEN DURING THE NEXT 24 TO 36 HOURS BEFORE A PORTION OF THE CIRCULATION MOVES OVER COOLER WATERS. NEITHER SHIPS NOR LGEM MODELS ARE VERY ENTHUSIASTIC ABOUT DALILA...AND IN FACT...THE LATEST HWRF ONLY INCREASES THE WIND SLIGHTLY. BASED ON CONTINUITY...THE OFFICIAL FORECAST STILL CALLS FOR DALILA TO REACH HURRICANE STATUS...BUT THIS IS BECOMING LESS LIKELY TO OCCUR. DALILA IS MOVING TOWARD THE NORTHWEST OR 310 DEGREES AT 8 KNOTS. A STRONG HIGH PRESSURE TO THE NORTH WILL SOON FORCE DALILA TO TAKE A MORE WESTERLY TRACK WITH A DECREASE IN FORWARD SPEED. THIS IS THE SOLUTION PROVIDED BY MOST OF THE GUIDANCE DURING THE NEXT 2 TO 3 DAYS. THEREAFTER...THE GUIDANCE BECOMES HIGHLY DIVERGENT SINCE SOME MODELS DEVELOP A LARGE DISTURBANCE TO THE EAST OF DALILA...AND SUGGEST THAT DALILA WILL ROTATE AROUND THE NEW DISTURBANCE. THE OFFICIAL FORECAST ASSUMES...BEYOND 3 DAYS...THAT DALILA INSTEAD WILL CONTINUE SLOWLY WESTWARD SOUTH OF THE SUBTROPICAL RIDGE. IF THE TREND TOWARD THE WEST CONTINUES AND DALILA DOES NOT INTENSIFY MUCH MORE...THE TROPICAL STORM WARNING FOR MEXICO WILL LIKELY NO LONGER BE REQUIRED. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 17.2N 105.1W 40 KT 45 MPH 12H 01/1800Z 18.0N 106.0W 45 KT 50 MPH 24H 02/0600Z 18.5N 106.8W 55 KT 65 MPH 36H 02/1800Z 18.8N 107.5W 65 KT 75 MPH 48H 03/0600Z 18.9N 108.3W 55 KT 65 MPH 72H 04/0600Z 19.0N 109.5W 55 KT 65 MPH 96H 05/0600Z 19.0N 111.5W 45 KT 50 MPH 120H 06/0600Z 19.0N 114.0W 35 KT 40 MPH $$ FORECASTER AVILA

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Tropical Storm DALILA Forecast Discussion Number 5

2013-07-01 04:32:49| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SUN JUN 30 2013 000 WTPZ44 KNHC 010232 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 PM PDT SUN JUN 30 2013 DURING THE PAST 6 HOURS...VISIBLE AND MICROWAVE SATELLITE IMAGERY INDICATES THAT THE INNER CORE STRUCTURE OF DALILA HAS IMPROVED. IN FACT...37 GHZ AND RADAR IMAGERY FROM A 30/1857Z TRMM OVERPASS REVEALED THAT A 70 PERCENT CLOSED LOW- TO MID-LEVEL EYEWALL HAD DEVELOPED. UPPER-LEVEL OUTFLOW HAS ALSO IMPROVED...ESPECIALLY IN THE NORTHWESTERN SEMICIRCLE. THE INITIAL INTENSITY OF 40 KT IS BASED ON A BLEND OF 45 KT...30 KT...AND 47 KT FROM TAFB...SAB... AND UW-CIMSS ADT...RESPECTIVELY. MICROWAVE AND VISIBLE SATELLITE FIXES SUGGEST THAT DALILA HAS BEEN WOBBLING ABOUT A MEAN MOTION OF 315/09 KT. THE MASSIVE HEAT WAVE RIDGE OVER THE SOUTHWESTERN U.S. EXTENDS SOUTHWARD INTO NORTHERN AND CENTRAL MEXICO...AND ALSO WESTWARD ACROSS BAJA CALIFORNIA. THIS STAGNANT STEERING PATTERN SHOULD KEEP DALILA MOVING NORTHWESTWARD TONIGHT...FOLLOWED BY A GRADUAL TURN TOWARD THE WEST-NORTHWEST LATE MONDAY AND TO THE WEST BY TUESDAY. THERE IS A LARGE SPREAD IN THE MODEL GUIDANCE...WITH THE ECMWF AND HWRF MODELS TAKING DALILA SOUTHWESTWARD BY 72 HOURS AS THE CYCLONE WEAKENS. HOWEVER...THE GFS AND GFS ENSEMBLE MEAN MODELS...WHICH HAVE BEEN FAIRLY STABLE THE PAST FEW CYCLES...KEEP DALILA MOVING IN A GENERAL WESTWARD DIRECTION LATE IN THE PERIOD AS A ROBUST TROPICAL STORM OR HURRICANE...AND THAT TRACK SCENARIO WAS CLOSELY FOLLOWED. ALTHOUGH THE VERTICAL SHEAR IS CURRENTLY LIGHT AT ONLY 3 KT...THE SHIPS INTENSITY MODEL INDICATES THAT THE SHEAR DIRECTION IS FROM A SOUTH-SOUTHEASTERLY DIRECTION. THE COMBINATION OF THE SHEAR AND SOME DRY AIR ENTRAINMENT INTO THE EASTERN SEMICIRCLE OF THE CYCLONE HAS KEPT MOST OF THE SIGNIFICANT DEEP CONVECTION DISPLACED TO THE NORTHWEST OF THE CENTER. HOWEVER...RECENT VISIBLE AND INFRARED IMAGERY INDICATE THAT MORE INNER CORE CONVECTION HAS BEGUN TO DEVELOP AROUND THE AFOREMENTIONED MICROWAVE EYE FEATURE...WHICH COULD BE A SIGNAL THAT AT LEAST SOME GRADUAL INTENSIFICATION SHOULD OCCUR DURING THE NEXT 48 HOURS BEFORE STRONGER SHEAR KICKS IN. DALILA IS A COMPACT TROPICAL CYCLONE...WHICH MEANS THAT IT IS SUSCEPTIBLE TO RAPID CHANGES CHANGES IN INTENSITY...BOTH UP AND DOWN. SO FOR NOW...A CONSERVATIVE FORECAST IS THE BEST COURSE OF ACTION UNTIL A SOLID INTENSIFICATION SIGNAL HAS BEEN ESTABLISHED. THE OFFICIAL INTENSITY FORECAST IS ONLY SLIGHTLY HIGHER THAN THE PREVIOUS ADVISORY...AND NOW SHOWS DALILA REACHING HURRICANE STRENGTH BY 48 HOURS...WHICH IS SLIGHTLY HIGHER THAN ALL OF THE NHC INTENSITY GUIDANCE. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 16.8N 104.4W 40 KT 45 MPH 12H 01/1200Z 17.5N 105.3W 45 KT 50 MPH 24H 02/0000Z 18.3N 106.3W 55 KT 65 MPH 36H 02/1200Z 18.7N 107.1W 60 KT 70 MPH 48H 03/0000Z 18.9N 107.7W 65 KT 75 MPH 72H 04/0000Z 19.0N 109.0W 55 KT 65 MPH 96H 05/0000Z 19.0N 110.6W 50 KT 60 MPH 120H 06/0000Z 19.0N 113.0W 40 KT 45 MPH $$ FORECASTER STEWART

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Tropical Storm DALILA Forecast Discussion Number 4

2013-06-30 22:42:48| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SUN JUN 30 2013 000 WTPZ44 KNHC 302042 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 200 PM PDT SUN JUN 30 2013 ALTHOUGH SITUATED IN AN ENVIRONMENT THAT SEEMS CONDUCIVE TO INTENSIFICATION...DALILA HAS NOT STRENGTHENED OVER THE PAST SEVERAL HOURS. IN FACT...THE CLOUD PATTERN HAS BECOME LESS ORGANIZED SINCE EARLIER TODAY...AND THE DEEP CONVECTION IS NOT IMPRESSIVE. A RECENT ASCAT OVERPASS INDICATES THAT THE CYCLONE IS OF MARGINAL TROPICAL STORM STRENGTH...SO THE CURRENT WIND SPEED ESTIMATE IS HELD AT 35 KT. SINCE CONDITIONS SHOULD FAVOR STRENGTHENING OVER THE NEXT COUPLE OF DAYS...THE OFFICIAL FORECAST CONTINUES TO SHOW WINDS APPROACHING HURRICANE FORCE IN ABOUT 48 HOURS. THE OFFICIAL WIND SPEED FORECAST IS A BLEND OF THE STATISTICAL-DYNAMICAL AND REGIONAL HURRICANE MODEL GUIDANCE...AND IS CLOSE TO THE LATEST FSU SUPERENSEMBLE PREDICTION. EVEN WITH HIGH-RESOLUTION VISIBLE IMAGES...THE CENTER HAS BEEN VERY DIFFICULT TO LOCATE ON GEOSTATIONARY IMAGERY. THANKS TO THE TIMELY ASCAT OVERPASS...A GOOD CENTER FIX WAS OBTAINED...AND THE INITIAL MOTION IS NEAR 330/8. A MID-TROPOSPHERIC RIDGE ASSOCIATED WITH A HIGH PRESSURE CENTER OVER THE SOUTHWESTERN U.S. SHOULD CAUSE THE TROPICAL CYCLONE TO TURN NORTHWESTWARD...WEST-NORTHWESTWARD...AND EVENTUALLY WESTWARD DURING THE FORECAST PERIOD. THE LATEST OFFICIAL TRACK FORECAST IS A LITTLE FASTER THAN THE PREVIOUS ONE IN THE EARLY PART OF THE FORECAST PERIOD...AND SLOWER IN THE LATTER PART. THIS IS SIMILAR TO BUT A LITTLE SLOWER THAN THE LATEST GFS SOLUTION. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 16.2N 103.7W 35 KT 40 MPH 12H 01/0600Z 17.0N 104.6W 40 KT 45 MPH 24H 01/1800Z 18.0N 105.7W 50 KT 60 MPH 36H 02/0600Z 18.8N 106.7W 55 KT 65 MPH 48H 02/1800Z 19.0N 107.3W 60 KT 70 MPH 72H 03/1800Z 19.0N 108.5W 55 KT 65 MPH 96H 04/1800Z 19.0N 110.0W 50 KT 60 MPH 120H 05/1800Z 19.0N 112.0W 40 KT 45 MPH $$ FORECASTER PASCH

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Tropical Storm DALILA Forecast Discussion Number 3

2013-06-30 16:31:49| National Hurricane Center (East Pacific)

Issued at 800 AM PDT SUN JUN 30 2013 000 WTPZ44 KNHC 301431 TCDEP4 TROPICAL STORM DALILA DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL EP042013 800 AM PDT SUN JUN 30 2013 SATELLITE IMAGES SHOW THAT THE COVERAGE AND INTENSITY OF DEEP CONVECTION HAS DIMINISHED SOMEWHAT OVER THE PAST FEW HOURS...AND BANDING FEATURES ARE NOT YET WELL-DEFINED. THE CURRENT INTENSITY ESTIMATE IS HELD AT 35 KT IN AGREEMENT WITH DVORAK ESTIMATES FROM TAFB AND SAB. DALILA IS EXPERIENCING SOME SOUTHERLY SHEAR...BUT THE ENVIRONMENT SHOULD BE FAVORABLE FOR SOME STRENGTHENING OVER THE NEXT 48 HOURS OR SO. THE OFFICIAL WIND SPEED FORECAST IS A LITTLE ABOVE THE STATISTICAL-DYNAMICAL GUIDANCE AND CLOSE TO THE INTENSITY MODEL CONSENSUS. RECENT CENTER FIXES SUGGEST THAT THE MOTION IS NOW NORTH-NORTHWEST OR NEAR 340/8. A MID-LEVEL RIDGE EXTENDING SOUTHEASTWARD FROM A STRONG HIGH PRESSURE AREA OVER THE SOUTHWESTERN U.S. IS EXPECTED TO INDUCE A GRADUAL TURN TOWARD THE LEFT DURING THE NEXT FEW DAYS. THE OFFICIAL TRACK FORECAST IS ONLY A LITTLE TO THE SOUTH OF THE PREVIOUS ONE BEYOND 48 HOURS...AND IS NEAR THE NORTHERN EDGE OF THE TRACK GUIDANCE MODEL ENVELOPE. GIVEN THE UNCERTAINTIES IN SIZE AND TRACK...THE TROPICAL STORM WARNING AND WATCH HAVE BEEN EXTENDED NORTHWARD ALONG THE SOUTHWESTERN COAST OF MEXICO. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 15.5N 103.2W 35 KT 40 MPH 12H 01/0000Z 16.4N 103.9W 40 KT 45 MPH 24H 01/1200Z 17.3N 104.7W 50 KT 60 MPH 36H 02/0000Z 18.0N 105.6W 55 KT 65 MPH 48H 02/1200Z 18.6N 106.4W 60 KT 70 MPH 72H 03/1200Z 19.0N 108.0W 60 KT 70 MPH 96H 04/1200Z 19.0N 109.5W 50 KT 60 MPH 120H 05/1200Z 19.0N 112.0W 40 KT 45 MPH $$ FORECASTER PASCH

Tags: number discussion storm tropical

 

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