Tropical Storm Erin - 4pm Thursday Advisory

By: National Hurricane Center
By: National Hurricane Center

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 NHCINTENSITY 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.


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