000WTPZ41 KNHC 151441TCDEP1TROPICAL DEPRESSION ONE-E DISCUSSION NUMBER 1NWS NATIONAL HURRICANE CENTER MIAMI FL EP012013800 AM PDT WED MAY 15 2013THE EASTERN NORTH PACIFIC HURRICANE SEASON HAS WASTED NO TIMEGETTING STARTED. THE LOW PRESSURE SYSTEM THAT WE HAVE BEENMONITORING SOUTH OF THE MEXICAN COAST BECAME BETTER ORGANIZEDOVERNIGHT...AND A NEARLY UNBROKEN BAND OF DEEP CONVECTION NOW WRAPSAROUND THE SOUTHERN AND WESTERN SIDE OF THE CIRCULATION. DVORAKINTENSITY ESTIMATES HAVE INCREASED AND ARE NOW T2.0 FROM TAFB ANDT1.5 FROM SAB...SO THE SYSTEM IS BEING DESIGNATED AS A 30-KTTROPICAL DEPRESSION.THE CURRENT MOTION ESTIMATE IS 280 DEGREES AT 10 KT. THE DEPRESSIONIS SITUATED ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE THATEXTENDS FROM THE BAY OF CAMPECHE SOUTHWESTWARD OVER THE PACIFICWATERS. EVEN THOUGH A MID-LEVEL TROUGH IS LIKELY TO AMPLIFY IN THEVICINITY OF CALIFORNIA IN THE COMING DAYS...THE DEPRESSION IS SOFAR SOUTH THAT ANY EFFECTS ON STEERING SHOULD BE MINIMAL. ANORTHWESTWARD MOTION IS POSSIBLE IN 4 TO 5 DAYS ONCE THE SYSTEMREACHES THE WESTERN END OF THE RIDGE. THERE IS SOME DISAGREEMENTAMONG THE GLOBAL MODELS TOWARD THE END OF THE FORECAST PERIOD...BUTTHE OFFICIAL FORECAST IS CLOSER TO THE SOLUTIONS THAT SHOW ASTRONGER SYSTEM...SPECIFICALLY THE GFS...BAM MEDIUM...AND BAM DEEP.THE DEPRESSION IS EMBEDDED IN A ZONE OF UPPER-LEVEL DIFFLUENCE TOTHE EAST OF THE SUBTROPICAL JET...AND IT WILL BE TRAVERSING THEWARMEST WATERS OF THE EASTERN NORTH PACIFIC OVER THE NEXT FEW DAYS. THIS SHOULD SUPPORT STRENGTHENING FOR AT LEAST THE NEXT 3 TO 4 DAYSBEFORE THE SYSTEM REACHES STRONG UPPER-LEVEL WESTERLIES ANDAPPROACHES COOLER WATERS. SINCE CONDITIONS APPEAR FAVORABLE...ITSEEMS REASONABLE THAT THE DEPRESSION SHOULD AT LEAST BE ABLE TOKEEP UP WITH A CLIMATOLOGICAL INTENSIFICATION RATE. THE OFFICIALFORECAST THEREFORE SHOWS FASTER STRENGTHENING AND A HIGHER PEAKINTENSITY THAN SHIPS AND LGEM SINCE THE CLIMATOLOGY-PERSISTENCEMODEL SHIFOR IS HIGHER THAN EITHER OF THOSE TWO MODELS.FORECAST POSITIONS AND MAX WINDSINIT 15/1500Z 8.2N 103.6W 30 KT 35 MPH 12H 16/0000Z 8.6N 105.3W 35 KT 40 MPH 24H 16/1200Z 9.1N 107.3W 45 KT 50 MPH 36H 17/0000Z 9.5N 108.9W 55 KT 65 MPH 48H 17/1200Z 10.0N 110.4W 65 KT 75 MPH 72H 18/1200Z 11.5N 113.0W 70 KT 80 MPH 96H 19/1200Z 13.0N 115.5W 65 KT 75 MPH120H 20/1200Z 15.5N 117.0W 55 KT 65 MPH$$FORECASTER BERG
000WTPZ41 KNHC 152036TCDEP1TROPICAL STORM ALVIN DISCUSSION NUMBER 2NWS NATIONAL HURRICANE CENTER MIAMI FL EP012013200 PM PDT WED MAY 15 2013ASCAT DATA FROM AROUND 1612 UTC SHOWED THAT THE DEPRESSION HAD WINDSVERY NEAR THE THRESHOLD FOR A TROPICAL STORM. THE CLOUD PATTERN INVISIBLE IMAGERY HAS BECOME MORE ORGANIZED SINCE THE TIME OF THATPASS...AND IT IS LIKELY THAT THE SYSTEM HAS BECOME A TROPICALSTORM. THE INTENSITY IS BEING SET AT 35 KT.THE ASCAT PASS ALSO HELPED TO BETTER LOCATE THE LOW-LEVELCENTER...AND THE INITIAL MOTION ESTIMATE IS NOW 290 DEGREES AT 11KT. ALVIN IS ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGETHAT EXTENDS SOUTHWESTWARD FROM MAINLAND MEXICO OVER THEPACIFIC...AND THIS FEATURE SHOULD CONTINUE TO STEER THE STORMWEST-NORTHWESTWARD FOR THE NEXT FEW DAYS. A MID-LEVEL TROUGH ISFORECAST TO AMPLIFY NEAR CALIFORNIA COAST IN 2 TO 3 DAYS...CREATINGA WEAKNESS IN THE RIDGE. THERE IS A SIGNIFICANT SPLIT IN THE MODELGUIDANCE WITH THE STRONGER GFS AND GFDL SHOWING A TURN TOWARD THENORTH AND THE WEAKER ECMWF AND UKMET MODELS SHOWING A CONTINUEDWESTWARD MOTION BY DAY 5. THE OFFICIAL FORECAST SOMEWHAT SPLITSTHE DIFFERENCE BUT DOES FAVOR THE SCENARIO OF A STRONGERNORTHWESTWARD-TURNING STORM.MOST OF THE INTENSITY GUIDANCE SUPPORTS ALVIN REACHING HURRICANESTRENGTH IN A FEW DAYS. THE DYNAMICAL GFDL AND HWRF MODELS ARE THEMOST AGGRESSIVE...BUT EVEN THE SHIPS MODEL SHOWS ALVIN GETTINGSTRONGER THAN WE INDICATED IN THE PREVIOUS OFFICIAL FORECAST. ALVIN IS ABOUT TO MOVE OVER A WARM POOL OF WATER WITH SEA SURFACETEMPERATURES AROUND 30.5C...AND VERTICAL SHEAR SHOULD BE MINIMALFOR AT LEAST THE NEXT 3 DAYS. THE NHC INTENSITY FORECAST CONTINUESTO SHOW A STEADY INTENSIFICATION AND HAS BEEN BUMPED UP SLIGHTLYFROM THE PREVIOUS FORECAST THROUGH DAY 3. FASTER STRENGTHENING ISPOSSIBLE...AND THE RAPID INTENSIFICATION INDEX NOW SHOWS A 1 IN 3CHANCE OF A 30-KT INCREASE IN WINDS OVER THE NEXT 24 HOURS. WEAKENING SHOULD BE UNDERWAY IN 4 TO 5 DAYS MAINLY DUE TO STRONGERVERTICAL WIND SHEAR.FORECAST POSITIONS AND MAX WINDSINIT 15/2100Z 8.7N 105.1W 35 KT 40 MPH 12H 16/0600Z 9.3N 106.5W 40 KT 45 MPH 24H 16/1800Z 10.0N 108.2W 50 KT 60 MPH 36H 17/0600Z 10.6N 109.8W 60 KT 70 MPH 48H 17/1800Z 11.1N 111.4W 70 KT 80 MPH 72H 18/1800Z 12.5N 114.0W 75 KT 85 MPH 96H 19/1800Z 14.0N 116.0W 60 KT 70 MPH120H 20/1800Z 15.5N 117.5W 40 KT 45 MPH$$FORECASTER BERG
TROPICAL STORM ALVIN DISCUSSION NUMBER 5NWS NATIONAL HURRICANE CENTER MIAMI FL EP012013800 AM PDT THU MAY 16 2013ALVIN APPEARS TO HAVE DEGRADED IN STRUCTURE OVERNIGHT. INFRAREDSATELLITE IMAGERY AND SCATTEROMETER DATA INDICATE THAT THECIRCULATION HAS HAD DIFFICULTY SEPARATING FROM THE ITCZ...AND THELOW-LEVEL CENTER IS LIKELY LOCATED ON THE WESTERN EDGE OF THE DEEPCONVECTION. THE INTENSITY IS BEING HELD AT 45 KT BASED ON THEEARLIER ASCAT DATA...BUT SATELLITE ESTIMATES SUGGEST THAT ALVINCOULD BE A BIT WEAKER.ALTHOUGH THE HISTORICALLY TWO BEST GLOBAL MODELS...THE GFS ANDECMWF...HAVE HAD SOME DISAGREEMENT ON ALVIN...EACH APPEARS TO HAVEBEEN RIGHT TO SOME DEGREE. THE GFS HAD A BETTER HANDLE ONGENESIS...BUT THE ECMWF MAY HAVE BEEN RIGHT THAT ALVIN WOULD NOTSTRENGTHEN SIGNIFICANTLY. AS OPPOSED TO YESTERDAY...THE SHIPSGUIDANCE NOW INDICATES THAT 15 TO 20 KT OF VERTICAL SHEAR WILLAFFECT ALVIN DURING THE NEXT FIVE DAYS...AND NEITHER OF THESTATISTICAL MODELS NOW SHOWS THE CYCLONE REACHING HURRICANESTRENGTH. THE PROSPECTS FOR SIGNIFICANT INTENSIFICATION APPEAR TOBE DWINDLING...AND THE OFFICIAL FORECAST ESSENTIALLY HOLDS THEINTENSITY STEADY FOR THE NEXT 48 HOURS. A MORE PRONOUNCED INCREASEIN WESTERLY SHEAR SHOULD BEGIN A DEFINITE WEAKENING TREND BY DAY3...AND ALVIN COULD DEGENERATE TO A REMNANT LOW NEAR THE END OF THEFORECAST PERIOD. NEEDLESS TO SAY...THERE IS STILL LOW CONFIDENCE INTHE INTENSITY FORECAST.SINCE THE OFFICIAL INTENSITY FORECAST HAS BEEN LOWERED...THE NHCTRACK FORECAST HAS BEEN SHIFTED A BIT FARTHER SOUTH AND WEST WITHTHE ASSUMPTION THAT LOWER-LEVEL FLOW WILL HAVE A GREATER INFLUENCEON STEERING. THE TRACK MODELS ARE IN BETTER AGREEMENT ON THEGENERAL DIRECTION TODAY ALTHOUGH THERE IS STILL A SPEEDDISCREPANCY...ESPECIALLY BETWEEN THE GFS AND ECMWF.FORECAST POSITIONS AND MAX WINDSINIT 16/1500Z 9.4N 107.7W 45 KT 50 MPH12H 17/0000Z 9.9N 108.8W 50 KT 60 MPH24H 17/1200Z 10.7N 110.5W 50 KT 60 MPH36H 18/0000Z 11.2N 112.3W 50 KT 60 MPH48H 18/1200Z 11.6N 113.6W 50 KT 60 MPH72H 19/1200Z 13.0N 116.0W 45 KT 50 MPH96H 20/1200Z 13.5N 118.5W 30 KT 35 MPH120H 21/1200Z 13.5N 120.5W 25 KT 30 MPH...POST-TROP/REMNT LOW$$FORECASTER BERG