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Tropical Storm ERIN Forecast Discussion Number 5
2013-08-16 04:45:19| National Hurricane Center (Atlantic)
Issued at 1100 PM AST THU AUG 15 2013 000 WTNT45 KNHC 160245 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 1100 PM AST THU AUG 15 2013 CONVECTION ASSOCIATED WITH ERIN HAS BEEN ON THE WANE DURING MOST OF THE EVENING HOURS...ALTHOUGH RECENTLY A SMALL BURST HAS FORMED EAST OF THE CENTER. MICROWAVE PASSES SUGGEST THE SYSTEM IS NOT WELL ORGANIZED...WITH THE LOW-LEVEL CENTER APPARENTLY WEST OF THE MID- LEVEL CENTER. THE INITIAL INTENSITY IS BEING HELD AT 35 KT IN AGREEMENT WITH THE DVORAK ESTIMATE FROM TAFB. THE OVERALL ENVIRONMENT FOR THE NEXT DAY OR TWO SEEMS TO BE CONDUCIVE FOR SOME STRENGTHENING WITH THE SHEAR FORECAST TO BE LIGHT BUT A LIMITING FACTOR OF MARGINAL SSTS. IN A FEW DAYS...ALTHOUGH SSTS ARE FORECAST TO INCREASE...THE GLOBAL MODELS SHOW AN INCREASE IN SHEAR...WHICH WOULD FACILITATE RATHER DRY AIR ALOFT ENTRAINING INTO THE CENTRAL CORE OF ERIN. THUS...THE OFFICIAL NHC FORECAST SHOWS WEAKENING AFTER DAY 3...WHICH IS CONSISTENT WITH THE PREVIOUS FORECAST AND THE FLORIDA STATE SUPERENSEMBLE. MICROWAVE FIXES GIVE AN INITIAL MOTION OF 295/13. THIS GENERAL COURSE IS EXPECTED FOR THE NEXT COUPLE OF DAYS WHILE A MID-LEVEL RIDGE REMAINS TO THE NORTHEAST OF THE TROPICAL CYCLONE. AFTER THAT TIME...THE BIGGEST UNCERTAINTY IS WHETHER A WEAKNESS IN THE RIDGE FROM A MID- TO UPPER-LEVEL LOW LOCATED OVER THE EASTERN ATLANTIC WILL ALLOW THAT TRACK TO CONTINUE. IF THE STORM IS SHALLOW ENOUGH...IT WILL PROBABLY MISS THE WEAKNESS AND INSTEAD TAKE A MORE WESTWARD TURN BECAUSE OF A STRONGER LOW-LEVEL RIDGE. ALTHOUGH THE NEW NHC FORECAST IS SHIFTED NORTHWARD TO COME INTO BETTER AGREEMENT WITH THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...IT IS STILL WELL TO THE SOUTH OF THE DYNAMICAL MODEL CONSENSUS. FURTHER ADJUSTMENTS COULD STILL BE NECESSARY IF THIS NORTHWARD TREND IN THE GUIDANCE PERSISTS IN FUTURE CYCLES. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 15.5N 29.1W 35 KT 40 MPH 12H 16/1200Z 16.3N 31.1W 35 KT 40 MPH 24H 17/0000Z 17.5N 33.4W 40 KT 45 MPH 36H 17/1200Z 18.6N 35.5W 45 KT 50 MPH 48H 18/0000Z 19.6N 37.4W 45 KT 50 MPH 72H 19/0000Z 20.5N 41.5W 45 KT 50 MPH 96H 20/0000Z 21.5N 46.0W 35 KT 40 MPH 120H 21/0000Z 22.5N 50.0W 30 KT 35 MPH $$ FORECASTER BLAKE
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