Tropical Storm Erin - 10am Thursday Discussion

By: National Hurricane Center
By: National Hurricane Center

TROPICAL STORM ERIN DISCUSSION NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052013
1100 AM AST THU AUG 15 2013

THE SATELLITE PRESENTATION OF THE CYCLONE HAS CONTINUED TO IMPROVE OVER THE PAST FEW HOURS. INFRARED IMAGERY SHOWS VERY COLD CLOUD TOPS SITUATED NEAR AND TO THE SOUTH OF THE ESTIMATED CENTER POSITION...WITH A SMALL BANDING FEATURE EXTENDING TO THE SOUTHWEST. THE INITIAL INTENSITY OF 35 KT IS SUPPORTED BY A BLEND OF THE LATEST OBJECTIVE AND SUBJECTIVE DVORAK ESTIMATES AND A 1102 UTC ASCAT-A PASS THAT SHOWED WINDS OF 32 KT. ERIN IS EXPECTED TO BE IN AN ENVIRONMENT THAT SUPPORTS SOME STRENGTHENING DURING THE NEXT COUPLE OF DAYS WITH SSTS OF 26-27C...LOW SHEAR...AND A MOIST ENVIRONMENT. BY DAY 3...THE SYSTEM WILL BE MOVING INTO A DRIER AND MORE STABLE ATMOSPHERIC ENVIRONMENT...WHICH SHOULD RESULT IN WEAKENING. THE GLOBAL MODELS AND THE HWRF SHOW A WEAK OR DISSIPATING SYSTEM BY DAY 5...HOWEVER THE SHIPS AND LGEM SHOW LITTLE CHANGE IN INTENSITY OR EVEN STRENGTHENING. THE OFFICIAL FORECAST LEANS A LITTLE TOWARD THE WEAKER SOLUTION AT DAYS 4 AND 5.

THE AFOREMENTIONED ASCAT PASS WAS ALSO HELPFUL IN LOCATING THE CENTER OF ERIN...WHICH IS A LITTLE SOUTH AND WEST OF PREVIOUS ESTIMATES. BASED ON A SOUTHWESTWARD ADJUSTMENT OF THE CENTER POSITION THE INITIAL MOTION ESTIMATE IS 285/13. ERIN IS CURRENTLY BEING STEERED BY A NARROW SUBTROPICAL RIDGE TO ITS NORTH...AND THE GUIDANCE IS IN GOOD AGREEMENT ON THIS MOTION CONTINUING FOR THE NEXT COUPLE OF DAYS. BY DAY 3...THE SPREAD IN THE GUIDANCE INCREASES. ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE THE GFDL... GFDL ENSEMBLE MEAN...ECMWF AND UKMET SHOW A NORTHWESTWARD OR WEST-NORTHWESTWARD MOTION. THE FIM...GFS...GFS ENSEMBLE MEAN AND HWRF ALL SHOW A WESTWARD TRACK...CONSISTENT WITH A SHALLOWER SYSTEM BEING STEERED BY THE LOW-LEVEL FLOW. THE NHC FORECAST AT DAYS 3 THROUGH 5 CONTINUES TO FOLLOW THIS SOUTHERN CAMP OF MODELS AND IS LARGELY AN UPDATE OF THE PREVIOUS NHC TRACK.


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