189  
FXUS07 KWBC 311906  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT SUN AUG 31 2025  
 
30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2025  
 
THE UPDATED MONTHLY OUTLOOK FOR SEPTEMBER 2025 IS BASED ON DYNAMICAL MODEL  
ENSEMBLES AND DETERMINISTIC RUNS OF THE GFS AND ECMWF MODELS OUT TO TWO WEEKS  
IN ADVANCE, THE MONTHLY CFS, THE OFFICIAL CPC TEMPERATURE AND PRECIPITATION  
OUTLOOKS FOR WEEKS 3-4, WEEK-2, 6-10 DAYS, WPC’S WEEK-1 FORECASTS, SEPTEMBER  
CLIMATOLOGY, RECENT OBSERVATIONS, SOIL MOISTURE ANOMALIES, COASTAL SEA-SURFACE  
TEMPERATURES (SSTS), AND MJO LAGGED TELECONNECTIONS. TROPICAL CYCLONE ACTIVITY  
IN THE ATLANTIC AND EAST PACIFIC BASINS WAS ALSO CONSIDERED, AS WELL AS THE  
LATE SEASON SOUTHWEST MONSOON AND POTENTIAL MOISTURE SURGES FROM THE GULF OF  
CALIFORNIA.  
 
THE UPDATED TEMPERATURE OUTLOOK FOR SEPTEMBER FAVORS ABOVE-NORMAL TEMPERATURES  
OVER SOUTHERN PORTIONS OF ALASKA, CONSISTENT WITH TEMPERATURE OUTLOOKS AT THE  
6-10 DAY, 8-14-DAY, AND WEEKS 3-4 TIME PERIODS, AND PROXIMITY TO ABOVE-AVERAGE  
SSTS. THIS AREA OF FAVORED ABOVE-NORMAL TEMPERATURES EXTENDS NORTHWARD UP THE  
WEST COAST OF ALASKA AND OVER MUCH OF THE NORTH SLOPE, AND HAS NOT CHANGED  
SINCE THE AUGUST 21ST OUTLOOK RELEASE. THIS IS PARTLY ATTRIBUTED TO THE  
CLIMATOLOGICALLY DELAYED FORMATION OF SEA ICE, AND PARTLY TO A MIXTURE OF NEAR-  
AND ABOVE-AVERAGE COASTAL SSTS. OVER THE LOWER 48 STATES, ABOVE-NORMAL  
TEMPERATURES ARE FAVORED FROM THE EASTERN INTERMOUNTAIN REGION AND ROCKIES  
EASTWARD TO THE NORTH-CENTRAL STATES. MAXIMUM FORECAST PROBABILITIES OF 50-60%  
ARE INDICATED OVER THE NORTHERN AND CENTRAL HIGH PLAINS, CONSISTENT WITH MANY  
OF THE OBJECTIVE MODELS AND TOOLS. THOUGH THE CFS IS BULLISH ON ABOVE-NORMAL  
TEMPERATURES OVER THE NORTHEASTERN STATES, THE CONSTITUENT OFFICIAL FORECASTS  
THAT MAKE UP THE MONTHLY PERIOD FAVOR BELOW-NORMAL TEMPERATURES DURING THE  
FIRST HALF OF SEPTEMBER SWITCHING TO ABOVE-NORMAL TEMPERATURES DURING THE  
SECOND HALF OF THE MONTH, WITH NO CLEAR MEAN TEMPERATURE ANOMALY INDICATED.  
FLORIDA IS ANOTHER AREA WHERE TEMPERATURES ARE UNCERTAIN, IN THIS CASE, WITH  
ABOVE-NORMAL TEMPERATURES FAVORED FOR THE FIRST HALF OF SEPTEMBER, CHANGING TO  
EQUAL CHANCES (EC) OF ABOVE-, NEAR-, AND BELOW-NORMAL TEMPERATURES FOR THE  
SECOND HALF OF THE MONTH. THIS ESSENTIALLY WIPES OUT ANY PREFERENCE FAVORING A  
PARTICULAR TEMPERATURE CATEGORY OVER FLORIDA. ELSEWHERE, WHICH INCLUDES A LARGE  
PORTION OF THE CONTIGUOUS U.S. (CONUS) AND A SUBSTANTIAL PART OF ALASKA, EC IS  
FAVORED.  
 
THE UPDATED PRECIPITATION OUTLOOK FOR SEPTEMBER FEATURES A TILT IN THE ODDS  
TOWARDS ABOVE-NORMAL PRECIPITATION FROM SOUTH-CENTRAL AND SOUTHEAST ALASKA TO  
THE PACIFIC NORTHWEST. THIS IS SUPPORTED TO VARIOUS DEGREES BY THE 6-10 DAY,  
8-14-DAY, AND WEEKS 3-4 PRECIPITATION OUTLOOKS. DURING WEEKS 3-4, BROAD LOW  
PRESSURE OVER THE NORTHEASTERN PACIFIC FAVORS WIDESPREAD ONSHORE FLOW ACROSS  
THESE AREAS. ABOVE-NORMAL PRECIPITATION IS ALSO FAVORED FROM CENTRAL PORTIONS  
OF THE PLAINS AND MISSISSIPPI VALLEY SOUTHWESTWARD ACROSS THE TEXAS PANHANDLE  
AND MUCH OF NEW MEXICO. THIS IS SUPPORTED BY MANY OF THE MODEL SOLUTIONS,  
ESPECIALLY OVER THE CENTRAL PORTIONS OF THE PLAINS AND MISSISSIPPI VALLEY, TIED  
TO EXPECTED FRONTAL ACTIVITY. THE SOUTHWESTWARD EXTENSION INTO NEW MEXICO IS  
LESS LIKELY (HENCE A MINIMAL TILT OF 33-40% TOWARD ABOVE-NORMAL PRECIPITATION).  
THIS EXTENSION WAS INCLUDED DUE TO SOME OF THE MODEL SOLUTIONS AND THE  
CONVERGENCE OF SEVERAL POSSIBLE FACTORS, INCLUDING BACK-DOOR COLD FRONTS AND  
ASSOCIATED UPSLOPE PRECIPITATION, LATE SEASON MONSOONAL ACTIVITY, AND THE  
POSSIBILITY OF A GULF SURGE ASSOCIATED WITH ANY RECURVING EAST PACIFIC TROPICAL  
CYCLONES. THE TROPICAL CYCLONE POSSIBILITY HAS SOME SUPPORT FROM CLIMATOLOGY  
AND LAGGED TELECONNECTIONS FROM THE MJO SUBSEASONAL SIGNAL, BASED ON THE MAIN  
ENHANCED CONVECTIVE ENVELOPE CURRENTLY OVER PHASE 3 (EASTERN INDIAN OCEAN AND  
MARITIME CONTINENT). THOUGH ARIZONA MAY EXPERIENCE ABOVE-NORMAL PRECIPITATION  
DURING THE WEEK-2 FORECAST PERIOD, IT DOESN’T LOOK LIKE THE EXPECTED TOTAL  
MONTHLY ACCUMULATION WILL BE ENOUGH TO WARRANT WETTER-THAN-NORMAL CONDITIONS  
FOR SEPTEMBER. ABOVE-NORMAL PRECIPITATION IS ALSO FAVORED FOR THE GULF-,  
SOUTHEAST-, AND MID-ATLANTIC COASTAL REGIONS. THIS SHOWS UP IN MANY OF THE  
MODEL SOLUTIONS, AND IS CONSISTENT WITH WHAT HAS BEEN A PERSISTENT THEME THIS  
SUMMER: STATIONARY FRONTS AND THE RESULTING LOW-LEVEL CONVERGENCE WHICH FOCUSES  
THE PRECIPITATION INTO ELONGATED BANDS. A CLIMATOLOGICAL FACTOR WHICH CANNOT BE  
IGNORED AT THIS TIME OF YEAR IS THE PEAK MONTH OF THE ATLANTIC HURRICANE SEASON  
IN SEPTEMBER. THE LONG-TRACK, CAPE VERDE-TYPE STORMS GENERALLY BEGIN TO GIVE  
WAY TO STORMS ORIGINATING IN THE GULF OF AMERICA AND CARIBBEAN SEA DURING THIS  
PERIOD. ELSEWHERE, THERE ARE NO AREAS OF FAVORED BELOW-NORMAL PRECIPITATION IN  
THE UPDATED SEPTEMBER OUTLOOK OVER THE CONUS OR ALASKA, DUE TO MANY DIFFERENT  
MODEL SCENARIOS. IN ADDITION, TRYING TO PINPOINT SMALL-SCALE AREAS OF SLIGHTLY  
BETTER AGREEMENT WHERE DRIER-THAN-NORMAL CONDITIONS ARE POSSIBLE IS NOT  
REALISTIC FOR THE MONTHLY TIMESCALE. FOR THE HAWAIIAN ARCHIPELAGO NEARING THE  
END OF ITS CLIMATOLOGICAL DRY SEASON, BELOW-NORMAL PRECIPITATION AMOUNTS ARE  
FAVORED FOR SEPTEMBER, ALONG WITH DROUGHT EXPECTED TO EITHER PERSIST OR DEVELOP.  
 
—------------ PREVIOUS MID-MONTH DISCUSSION IS SHOWN BELOW —---------  
 
EL NIñO SOUTHERN OSCILLATION (ENSO) NEUTRAL CONDITIONS ARE PRESENT WITH SEA  
SURFACE TEMPERATURES (SSTS) NEAR AVERAGE ACROSS MOST OF THE EQUATORIAL PACIFIC  
OCEAN. THE MADDEN-JULIAN OSCILLATION (MJO) IS CURRENTLY CHARACTERIZED BY ITS  
ENHANCED CONVECTIVE PHASE CROSSING THE INDIAN OCEAN, WITH THE BULK OF THE  
ASSOCIATED TROPICAL RAINFALL LOCATED OVER THE MARITIME CONTINENT REGION. THE  
LATEST MJO FORECASTS FROM DYNAMICAL MODELS INDICATE CONSIDERABLE UNCERTAINTY IN  
THE EXPECTED EVOLUTION OF THE MJO DURING THE NEXT SEVERAL WEEKS.  
 
THE SEPTEMBER 2025 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON A  
COMBINATION OF DYNAMICAL MODELS, INCLUDING CFSV2, THE NORTH AMERICAN  
MULTI-MODEL ENSEMBLE (NMME), THE COPERNICUS CLIMATE SYSTEM (C3S), AND TO A  
LESSER EXTENT STATISTICAL MODELS/TOOLS SUCH AS THE CANONICAL CORRELATION  
ANALYSIS (CCA), CONSTRUCTED ANALOG ON SOIL MOISTURE (CAS), OPTIMAL CLIMATE  
NORMALS (OCN), AND A COMBINED ENSO-OCN TOOL. THE MONTHLY OUTLOOKS ARE ALSO  
BASED ON DYNAMICAL MODELS AND STATISTICAL TOOLS FOR THE WEEKS 3-4 PERIOD WHICH  
COVER THE EARLY AND MIDDLE THIRDS OF SEPTEMBER. UNCERTAINTY REGARDING THE  
EVOLUTION OF THE MJO PRECLUDED ITS USE AS A VIABLE TOOL IN THE CONSTRUCTION OF  
THE SEPTEMBER OUTLOOK. IMPACTS FROM THE MJO WILL BE RE-EVALUATED AT THE END OF  
THE MONTH FOR THE UPDATED VERSION OF THIS OUTLOOK. LOCAL SSTS AND ANTECEDENT  
SOIL MOISTURE ANOMALIES ALSO CONTRIBUTED TO THIS OUTLOOK WHERE APPLICABLE.  
 
THE SEPTEMBER 2025 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL TEMPERATURES ACROSS  
MOST OF THE CONTIGUOUS UNITED STATES (CONUS). THE REGIONS OF HIGHEST  
PROBABILITIES (REACHING 60 TO 70%) ARE LOCATED OVER THE UPPER FOUR  
CORNERS/CENTRAL ROCKIES AREA AND OVER NEW ENGLAND. FOR THE FORMER REGION OVER  
THE WEST WHICH INCLUDES A BROADER 50-60% AREA ENCOMPASSING MUCH OF THE INTERIOR  
WEST, ROCKIES, AND SOUTHERN HIGH PLAINS, THE OUTLOOK IS CONSISTENT WITH A  
MAJORITY OF THE DYNAMICAL AND STATISTICAL TOOLS. A SOMEWHAT BROADER 50-60% AREA  
IS ALSO FAVORED OVER MOST OF THE NORTHEAST, BASED ON MANY OF THE DYNAMICAL  
MODELS/TOOLS, HISTORICAL TRENDS (AS INDICATED BY THE OCN TOOL), AND TO SOME  
EXTENT THE PROXIMITY OF RELATIVELY WARM COASTAL WATERS OF THE WESTERN ATLANTIC.  
ELSEWHERE, PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES ARE ELEVATED  
(50-60%) OVER MOST OF THE FLORIDA PENINSULA, BASED ON VARIOUS TOOLS AND A  
STRONG TREND SIGNAL. FROM THE NORTH-CENTRAL CONUS TO THE GULF AND SOUTHEAST  
COASTS (EXCLUDING FLORIDA), DISCREPANCIES BETWEEN MODELS AND COMPARATIVELY  
WEAKER OVERALL WARM SIGNALS COMPARED TO OTHER PORTIONS OF THE CONUS CALL FOR  
MODEST PROBABILITIES TILTING TOWARD ABOVE-NORMAL TEMPERATURES (33-40%). FOR THE  
COAST OF SOUTHERN CALIFORNIA, EQUAL CHANCES (EC) OF ABOVE, NEAR, AND  
BELOW-NORMAL TEMPERATURES ARE FAVORED DUE TO THE PROXIMITY OF NEAR TO  
BELOW-NORMAL SEA-SURFACE TEMPERATURES (SSTS) NEAR THE COAST. IN ALASKA,  
ABOVE-NORMAL TEMPERATURE CHANCES ARE ELEVATED OVER THE WESTERN AND SOUTHERN  
MAINLAND, THE ALASKA PENINSULA AND EASTERN ALEUTIANS, AND SOUTHEAST ALASKA.  
THIS IS LARGELY ATTRIBUTED TO THE CALIBRATED C3S TOOL, PERSISTENCE OF THE AREA  
OF AGREEMENT BETWEEN THE ECMWF AND GEFS WEEKS 3-4 TEMPERATURE TOOLS, AND  
RELATIVELY WARM COASTAL SSTS. THE HIGHER CHANCES FOR ABOVE-NORMAL TEMPERATURES  
(50-60%) OVER NORTHWESTERN PORTIONS OF THE MAINLAND ARE BASED ON HISTORICAL  
TRENDS THAT FAVOR A DELAY IN THE ONSET OF SEA ICE FORMATION. FOR THE REMAINDER  
OF THE MAINLAND AND THE WESTERN ALEUTIANS, EC IS FAVORED.  
 
THE SEPTEMBER 2025 PRECIPITATION OUTLOOK FAVORS ELEVATED ODDS OF ABOVE-NORMAL  
PRECIPITATION FROM THE EASTERN GULF REGION (INCLUDING FLORIDA) ACROSS THE  
SOUTHEAST AND MID-ATLANTIC COAST. MUCH OF THE DYNAMICAL AND STATISTICAL  
GUIDANCE WARRANTS THESE ELEVATED ODDS OF ABOVE-NORMAL PRECIPITATION, AS DOES  
THE CLIMATOLOGICAL PEAK OF ATLANTIC TROPICAL CYCLONE ACTIVITY IN SEPTEMBER. IN  
ADDITION, THIS ENHANCED WET SIGNAL IS CONSISTENT WITH AN INCREASED LIKELIHOOD  
OF STALLED FRONTS.  
 
FOR THE PACIFIC NORTHWEST, SOME (BUT NOT ALL) OF THE TOOLS SUPPORT INCREASED  
CHANCES OF ABOVE-NORMAL PRECIPITATION, WITH SEPTEMBER BEING THE CLIMATOLOGICAL  
TRANSITION MONTH FROM DRY TO WET SEASON. FROM MOST OF THE INTERIOR WEST,  
ROCKIES, HIGH PLAINS, EXTENDING EASTWARD INTO THE OZARKS ODDS FAVOR  
BELOW-NORMAL PRECIPITATION, WITH MAXIMUM PROBABILITIES OF 50-60% OVER A SIZABLE  
MULTI-STATE AREA CENTERED NEAR THE GREAT SALT LAKE IN NORTHERN UTAH. TO VARYING  
DEGREES THIS IS BASED ON THE NMME CONSOLIDATION, THE CFSV2, AND A FEW  
CONSTITUENT MODELS OF THE C3S SUITE. THE EASTWARD EXTENSION OF THE RELATIVE  
DRYNESS ACROSS THE SOUTH-CENTRAL PLAINS AND OZARKS AREA IS BASED ON RECENT SOIL  
MOISTURE ANOMALIES. HOWEVER, PROBABILITIES ARE MODEST GIVEN THE UNCERTAINTY IN  
HOW MUCH PRECIPITATION MAY FALL OVER THIS REGION IN SEPTEMBER. OVER FAR  
SOUTHERN PORTIONS OF THE SOUTHWEST A TOKEN EC IS INDICATED DUE TO THE  
POSSIBILITY OF A GULF SURGE OR A RECURVING EAST PACIFIC HURRICANE BRINGING  
PRECIPITATION INTO THIS AREA DURING THE MONTH OF SEPTEMBER. WELL TO THE NORTH,  
ABOVE-NORMAL PRECIPITATION IS SLIGHTLY FAVORED OVER SOUTHEAST ALASKA. DUE TO  
CONFLICTING INDICATIONS AMONG THE DYNAMICAL AND STATISTICAL MODELS/TOOLS, THIS  
OUTLOOK FOR ALASKA IS BASED ON PERSISTENCE OF THE WEEKS 3-4 PRECIPITATION  
SIGNALS FROM THE CFS, GEFS, AND ECMWF MODELS, THE 30-DAY UNCALIBRATED C3S, THE  
METEO-FRANCE MODEL, AND THE PROXIMITY OF RELATIVELY WARM SSTS. FOR THE  
REMAINDER OF ALASKA, EC IS FAVORED FOR THE PRECIPITATION OUTLOOK.  
 
FORECASTER: ANTHONY ARTUSA  
 
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, FOLLOWING  
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3  
COMPLETE DECADES AS THE CLIMATE REFERENCE PERIOD. THE PROBABILITY ANOMALIES  
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT  
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.  
 
THE NEXT MONTHLY OUTLOOK...FOR OCT ... WILL BE ISSUED ON THU SEP 18 2025  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.  
 
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