585  
FXUS02 KWBC 261938  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
338 PM EDT MON SEP 26 2022  
 
VALID 12Z THU SEP 29 2022 - 12Z MON OCT 03 2022  
 
...HURRICANE IAN IS FORECAST TO INTENSIFY OVER THE EASTERN GULF OF  
MEXICO THEN SLOW AS IT TRACKS OFF THE FLORIDA GULF COAST LATER  
THIS WEEK, INCREASING THE THREAT FOR EXCESSIVE RAIN FROM FLORIDA  
INTO THE SOUTHEAST AMONG OTHER TROPICAL CYCLONE IMPACTS...  
 
   
..OVERVIEW
 
 
CONFIDENCE IS INCREASING IN A SLOWER IAN TRACKING OVER THE  
NORTHEAST GULF NEAR OR ALONG THE FLORIDA GULF COAST WEDNESDAY INTO  
FRIDAY. THE SYSTEM IS FORECAST TO WEAKEN PRIOR TO LANDFALL, BUT  
THE SLOWER SYSTEM WILL INCREASE THE RISK FOR EXCESSIVE RAINFALL  
FOR FLORIDA INTO THE SOUTHEAST. PLEASE SEE THE LATEST WPC AND NHC  
PRODUCTS FOR MORE INFORMATION ON IAN FORECAST AND IMPACTS.  
ELSEWHERE, THE PROGRESSION OF OF AN EASTERN PACIFIC TROUGH/LOW  
OVER THE NORTHERN ROCKIES THURSDAY AND THE NORTHERN PLAINS OVER  
THE WEEKEND.  
   
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
 
 
A SLOWER AND A BIT FARTHER EAST TRACK TO IAN FROM THURSDAY AND  
FRIDAY THEN BECOMES MORE UNCERTAIN EAST-WEST WITH THE 12Z ECM  
FARTHER WEST AND THE 12Z GFS FARTHER EAST (AND THE 12Z UKMET EVEN  
FARTHER EAST). HOWEVER, ALL 12Z GUIDANCE HAS COME IN SLOWER AND  
GAINING LESS LATITUDE THIS WEEKEND BEFORE SLIDING EAST EARLY NEXT  
WEEK. REMARKABLE AGREEMENT BETWEEN THE 00Z ECMWF AND 06Z GFS GAVE  
CONFIDENCE IN RELYING ON THOSE MODELS THROUGH DAY 6 FOR BOTH THE  
FRONTAL PROGRESSIONS ACROSS THE CONUS AND QPF OVER THE NORTHERN  
ROCKIES AND THE HEAVY IAN-RELATED QPF IN THE SOUTHEAST. THAT  
AGREEMENT CONTINUES WITH THE 12Z ECMWF/GFS, PARTICULARLY FOR THE  
RIDGE DEVELOPING UP THE WEST COAST FRIDAY AND LOW/TROUGH THIS  
WEEKEND OVER THE NORTH-CENTRAL ROCKIES. THE 12Z CMC/UKMET CONTINUE  
TO DIFFER FROM THE GFS/EC CONSENSUS LIKE THEY DID AT 00Z, SO THOSE  
MODELS WERE REPLACED WITH THE GEFS AND ECENS MEANS FOR DAYS 6/7.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
HURRICANE IAN IS FORECAST PRODUCE NOTABLE RAINFALL AND WIND  
THREATS DURING THE PERIOD TO FLORIDA AND THE SOUTHEAST. A STALLING  
FRONT OVER FL WILL THEN LIFT NORTH WITH THE SYSTEM. STRONG HIGH  
PRESSURE TRACKING FROM THE GREAT LAKES AND STALLING OVER THE  
NORTHEAST INTO SATURDAY AND THEN REINFORCED WITH HIGH PRESSURE  
FROM HUDSON BAY TO NEW ENGLAND SUNDAY/MONDAY WILL HELP TO ENHANCE  
THE WINDS/ONSHORE FLOW TO THE NORTH OF IAN. THE HEAVY RAIN THREAT  
LIFTS FROM NORTHERN FLORIDA THURSDAY NIGHT THROUGH FRIDAY, WITH  
THE QPF FOCUS OVER THE CAROLINA COAST FRIDAY BEFORE LIFTING TOWARD  
AND INTO, BUT POSSIBLY NOT THROUGH THE MID-ATLANTIC OVER THE  
WEEKEND INTO MONDAY. THE EXPERIMENTAL DAY 4 EXCESSIVE RAINFALL  
OUTLOOK MAINTAINS SLIGHT/MODERATE RISK FOR NORTHERN FLORIDA INTO  
SOUTHEAST GEORGIA. A DAY 5 MODERATE RISK HAS BEEN RAISED FROM THE  
GREATER CHARLESTON TO GREATER SAVANNAH METRO AREAS WITH THE SLIGHT  
RISK CONTINUING FOR FAR NORTHERN FLORIDA, MUCH OF GEORGIA, ALL OF  
SOUTH CAROLINA, AND SOUTHERN NORTH CAROLINA.  
 
THE COMBINATION OF ANOMALOUS MOISTURE AND THE UPPER TROUGH/LOW  
EMERGING FROM THE NORTHWEST SHOULD PRODUCE AREAS OF LOCALLY HEAVY  
RAINFALL IN PORTIONS OF THE FOUR CORNERS STATES AND UP THE CENTRAL  
TO NORTHERN ROCKIES THURSDAY/FRIDAY. THIS SPREADS ONTO THE  
NORTHERN PLAINS SATURDAY INTO SUNDAY. SNOW LEVELS DROP TO AROUND  
9000FT IN THE NORTHERN ROCKIES UNDER THIS UPPER LOW.  
 
CLOUD COVER/RAIN FROM IAN AND CANADIAN HIGH PRESSURE FARTHER NORTH  
WILL MAKE MOST OF THE EASTERN CONUS WITH MAX TEMPS AS MUCH AS  
10-15F BELOW NORMAL INTO THIS WEEKEND. THE NORTHERN HIGH PLAINS  
WILL BE QUITE WARM ON THURSDAY WITH MAX TEMPS LEAST 15F ABOVE  
NORMAL. THIS MODERATES A BIT AS IT SHIFTS EAST OVER THE REST OF  
THE NORTHERN PLAINS FRIDAY/SATURDAY. THE UPPER TROUGH/LOW DRIFTING  
INTO THE ROCKIES/HIGH PLAINS WILL BRING MODERATELY BELOW NORMAL  
HIGHS IN ITS VICINITY FRIDAY/SATURDAY WITH ABOVE NORMAL  
TEMPERATURES RETURNING TO THE PACIFIC NORTHWEST COAST  
SATURDAY/SUNDAY UNDER THE BUILDING RIDGE.  
 
JACKSON  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL  
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE  
AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 

 
 
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