EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1154 AM EDT THU AUG 27 2015 VALID 12Z SUN AUG 30 2015 - 12Z THU SEP 03 2015 ...ERIKA MAY THREATEN FL/SERN COAST BY NEXT WEEK WITH WINDS/WAVES/HEAVY RAINS... ...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES... EXPECT THE LARGE SCALE PATTERN TO FEATURE A FAIRLY AMPLIFIED WEST COAT MEAN TROUGH AND BROAD RIDGE DOWNSTREAM WITH A HINT OF MEAN TROUGHING OVER THE CANADIAN MARITIMES/NEW ENGLAND. EMBEDDED WITHIN THE OVERALL MEAN RIDGE... GUIDANCE SHOWS MULTIPLE PIECES OF MID LVL ENERGY INITIALLY WITHIN A WEAKNESS FROM THE GRTLKS TO CNTRL-WRN GULF COAST. UNCERTAINTY OVER THE FINER DETAILS OF FLOW ALOFT OVER THE ERN CONUS/WRN ATLC BY THE LATTER HALF OF THE PERIOD LEADS TO BELOW AVG CONFIDENCE FOR THE ULTIMATE TRACK OF ERIKA. CONSULT LATEST NATIONAL HURRICANE CENTER PRODUCTS FOR FURTHER INFO REGARDING T.S. ERIKA WHICH IS FCST TO STRENGTHEN TO HURCN STATUS BY EARLY NEXT WEEK. EXTRAPOLATION OF THE 1500 UTC ADVISORY LEADS TO A DAYS 6-7 WED-THU TRACK OFF THE SERN COAST... WITH A SOMEWHAT SLOWER TREND RELATIVE TO CONTINUITY BASED ON A SWD ADJUSTMENT FOR INITIAL POSN AS PER THE AFOREMENTIONED ADVISORY. NOTE THAT ENSEMBLE SPREAD IS QUITE BROAD ALREADY BY DAY 4 MON AND EXPANDS FURTHER THEREAFTER. OPERATIONAL SOLNS BECOME INCREASINGLY DIVERSE AS WELL. THIS IS NOT SURPRISING GIVEN THE RELATIVELY SMALLER SCALE AND WEAK NATURE OF ONE OR MORE POTENTIALLY IMPORTANT SHRTWV IMPULSES TO THE N AND W OF ERIKA. AFTERNOON ISSUANCE OF WPC PROGS WILL REFLECT 1700 UTC NHC/WPC COORDINATION FOR DAYS 6-7. IN CONTRAST TO THE SITUATION OVER/NEAR THE SERN STATES... MODEL/ENSEMBLE GUIDANCE DISPLAYS BETTER THAN AVG CLUSTERING WITHIN THE WEST COAST MEAN TROUGH. A LEADING SHRTWV SHOULD EJECT FROM THE NORTHWEST DAY 3 SUN WITH A BRIEF FLATTENING OF THE TROUGH BEFORE ANOTHER DEFINED SHRTWV SHARPENS THE TROUGH BY DAY 7 THU. THERE IS SOMEWHAT MORE SPREAD WITH THE SHALLOW MEAN TROUGH THAT MAY BRUSH NEW ENGLAND AND THE CANADIAN MARITIMES. BASED ON REASONABLE CONSENSUS OVER THE WEST/NORTH THE STARTING BLEND PRIMARILY ACCOUNTS FOR THE TRACK OF ERIKA BY WAY OF A COMPROMISE PRIMARILY AMONG THE 12Z/26 ECMWF AND 00Z/06Z GFS INTO DAY 5 TUE... WITH MINIMAL INCLUSION OF THE 00Z GEFS/ECMWF MEANS. SOME 12Z/26 ECMWF AND 06Z GFS INPUT WAS MAINTAINED INTO DAYS 6-7 WED-THU WITH ENSMEAN WEIGHTING INCREASED SOMEWHAT COMPARED TO EARLIER IN THE PERIOD. ...SENSIBLE WEATHER HIGHLIGHTS... LOCATIONS ESPECIALLY OVER FLORIDA AND ALONG THE SERN COAST WILL NEED TO MONITOR FCSTS FOR ERIKA WITH POTENTIAL IMPACTS INCLUDING STRONG WINDS/HIGH WAVES/HVY RNFL. RELATIVELY LOW PREDICTABILITY OF FEATURES THAT MAY INFLUENCE THE STEERING/EVOLUTION OF ERIKA AT THE EXTENDED TIME FRAME LEADS TO BELOW AVG CONFIDENCE IN FORECASTING PRECISE EFFECTS AT PARTICULAR LOCATIONS AT THIS TIME. THE LARGE SCALE PATTERN WILL FAVOR BELOW NORMAL HIGHS ALONG/INLAND FROM THE WEST COAST WITH ONE OR MORE EPISODES OF ENHANCED RNFL ALONG FAVORED TERRAIN OF THE PAC NW... AND FARTHER EWD A BROAD AREA OF ABOVE NORMAL TEMPS FROM MOST OF THE PLAINS ACROSS THE MIDWEST INTO THE NORTHEAST. SOME LOCATIONS MAY SEE MULTIPLE DAYS WITH PLUS 10F OR GREATER ANOMALIES. A MEAN FRONTAL BNDRY MAY SERVE AS A FOCUS FOR SOME CONVECTION OVER THE EXTREME NRN TIER... MONSOONAL MSTR/SHRTWV IMPULSES WILL LIKELY SUPPORT PERIODS OF CONVECTION OVER THE SRN HALF OF THE ROCKIES... AND A WEAK UPR LOW MAY ENHANCE RNFL ALONG PORTIONS OF THE WRN HALF OF THE GULF COAST. SHRTWV ENERGY INITIALLY OVER THE GRTLKS COULD ALSO GENERATE SOME SHWRS/TSTMS. RAUSCH