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Tropical Storm ERIN Forecast Discussion Number 4
2013-08-15 22:32:16| National Hurricane Center (Atlantic)
Issued at 500 PM AST THU AUG 15 2013 000 WTNT45 KNHC 152032 TCDAT5 TROPICAL STORM ERIN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013 500 PM AST THU AUG 15 2013 THE CONVECTIVE PATTERN OF ERIN HAS EVOLVED INTO ONE THAT FEATURES MORE BANDING AWAY FROM THE CENTER AND WARMER CLOUD TOPS NEAR THE CENTER ITSELF. THE INITIAL INTENSITY REMAINS 35 KT BASED ON THE LATEST TAFB DVORAK ESTIMATE. THE INTENSITY FORECAST REASONING REMAINS UNCHANGED. FOR THE NEXT COUPLE OF DAYS...THE CYCLONE WILL BE MOVING THROUGH A MOIST LOW-SHEAR ENVIRONMENT WITH SSTS OF 26-27C...WHICH SHOULD SUPPORT MODEST STRENGTHENING. LATER IN THE PERIOD...ALTHOUGH SSTS INCREASE...ERIN WILL BE MOVING INTO A DRIER MORE STABLE ATMOSPHERE...AND WEAKENING IS EXPECTED. THE NHC INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ONE AND IS CLOSE TO THE INTENSITY CONSENSUS THROUGH 72 HOURS AND THEN FOLLOWS THE TREND OF THE DYNAMICAL MODELS...SHOWING GRADUAL WEAKENING. THE INITIAL MOTION ESTIMATE IS 290/12...AS THE CYCLONE APPEARS TO HAVE TURNED A BIT TO THE RIGHT DURING THE PAST FEW HOURS. THERE HAS BEEN A SIZEABLE NORTHWARD SHIFT IN NEARLY ALL OF THE TRACK MODEL GUIDANCE THIS CYCLE. THE GLOBAL MODELS NOW SHOW A DEEPER REPRESENTATION OF ERIN MOVING MORE INTO A WEAKNESS IN THE SUBTROPICAL RIDGE TO THE SOUTH OF A MID/UPPER-LEVEL LOW THAT WILL BE MEANDERING SOUTH OF THE AZORES. AS A RESULT...THE MODELS SHOW ERIN GAINING MORE LATITUDE DURING THE FIRST 72 HOURS OR SO. AFTER THAT...A TURN BACK TOWARD THE LEFT IS SHOWN BY MOST OF THE MODELS AS THE CYCLONE WEAKENS. FOR THIS CYCLE A NORTHWARD ADJUSTMENT HAS BEEN MADE TO THE NHC FORECAST...BUT THE NHC TRACK IS ON THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...ESPECIALLY AT DAYS 3 THROUGH 5. FURTHER ADJUSTMENTS WILL LIKELY BE NECESSARY IF THIS NORTHWARD TREND IN THE GUIDANCE PERSISTS IN FUTURE CYCLES. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 15.0N 27.5W 35 KT 40 MPH 12H 16/0600Z 15.6N 29.6W 40 KT 45 MPH 24H 16/1800Z 16.7N 32.0W 45 KT 50 MPH 36H 17/0600Z 17.5N 34.2W 45 KT 50 MPH 48H 17/1800Z 18.3N 36.3W 50 KT 60 MPH 72H 18/1800Z 19.0N 40.5W 50 KT 60 MPH 96H 19/1800Z 19.5N 44.5W 45 KT 50 MPH 120H 20/1800Z 20.0N 49.0W 35 KT 40 MPH $$ FORECASTER BRENNAN
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