PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
300PM EDT TUESDAY AUG 31 2010

30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2010

LA NINA CONDITIONS DEVELOPED DURING JULY, AS SEA SURFACE TEMPERATURE ANOMALIES 
STRENGTHENED ACROSS THE CENTRAL AND EASTERN EQUATORIAL PACIFIC OCEAN. THE 
SUBSURFACE HEAT CONTENT CONTINUED TO REFLECT A DEEP LAYER OF BELOW-AVERAGE 
TEMPERATURES EAST OF THE DATE LINE. IN ADDITION, CONVECTION WAS ENHANCED OVER 
INDONESIA AND REMAINED SUPPRESSED OVER THE WESTERN AND CENTRAL TROPICAL 
PACIFIC. ENHANCED LOW-LEVEL EASTERLY TRADE WINDS AND ANOMALOUS UPPER-LEVEL 
WESTERLY WINDS CONTINUED OVER THE WESTERN AND CENTRAL EQUATORIAL PACIFIC.  
NEARLY ALL MODELS PREDICT LA NINA TO CONTINUE THROUGH EARLY 2011, AND GIVEN THE 
STRONG COOLING OBSERVED OVER THE LAST SEVERAL MONTHS AND THE APPARENT 
OCEAN-ATMOSPHERE COUPLING (POSITIVE FEEDBACK)LA NINA CONDITIONS ARE EXPECTED TO 
STRENGTHEN AND LAST THROUGH THE NORTHERN HEMISPHERE WINTER 2010-11.

THE UPDATED SEPTEMBER 2010 MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOKS 
INCORPORATE INFORMATION FROM THE LATEST DYNAMICAL WEATHER PREDICTION MODELS AS 
WELL AS MONTHLY TEMPERATURE AND PRECIPITATION FORECASTS FROM THE NCEP CLIMATE 
FORECAST SYSTEM (CFS) COUPLED OCEAN-ATMOSPHERE DYNAMICAL MODEL. THIS 
INFORMATION HAS BEEN BLENDED WITH INFORMATION THAT WAS AVAILABLE FOR THE HALF 
MONTH LEAD SEPTEMBER OUTLOOK: THE CFS, CCA, SMLR, OCN, CAS AND SOME INFORMALLY 
USED TOOLS SUCH AS COASTAL SSTS, THE CONSTRUCTED ANALOGUE ON GLOBAL SST 
(CA-SST), ENSO COMPOSITES FOR THE ASO SEASON AND THE CONSIDERATION OF AN ACTIVE 
HURRICANE SEASON. 

THE UPDATED TEMPERATURE OUTLOOK FOR SEPTEMBER IS FAIRLY CONSISTENT WITH THE 
HALF MONTH LEAD FORECAST, CONTINUING TO FAVOR ABOVE AVERAGE TEMPERATURES OVER 
LARGE PARTS OF THE EASTERN HALF OF THE NATION AND THE SOUTHWEST AND BELOW 
AVERAGE TEMPERATURES IN THE PACIFIC NORTHWEST.  THE DYNAMICAL MODELS INDICATE A 
TROUGH DEVELOPING OVER THE NORTHWESTERN PART OF THE NATION DURING THE FIRST 
HALF OF THE MONTH AND DOWNSTREAM RIDGING AFFECTING THE CENTRAL AND EASTERN 
PART.  THIS CIRCULATION PATTERN IS CONSISTENT WITH EXPECTATIONS FROM THE LONG 
LEAD FORECAST AND RESULTS IN ONLY VERY SLIGHT CHANGES TO THAT FORECAST. 

THE UPDATED SEPTEMBER PRECIPITATION OUTLOOK REMAINS CONSISTENT WITH THE HALF 
MONTH LEAD OUTLOOK, ALTHOUGH A REGION WITH AN ENHANCED LIKELIHOOD OF ABOVE 
MEDIAN PRECIPITATION HAS BEEN ADDED OVER THE WESTERN GREAT LAKES REGION.  THIS 
REGION IS FAVORED TO HAVE ABOVE MEDIAN PRECIPITATION IN THE SHORT TERM AS WELL 
AS IN THE 6-10 AND WEEK 2 PERIODS.  THE ONLY OTHER CHANGE TO THIS FORECAST WAS 
TO EXTEND THE REGION FAVORED TO HAVE ABOVE MEDIAN PRECIPITATION UP INTO EXTREME 
EASTERN MASSACHUSETTS, AS THEY COULD SEE LARGE RAINFALL TOTALS EARLY IN THE 
MONTH ASSOCIATED WITH HURRICANE EARL, DEPENDENT ON THE EXACT TRACK OF THIS 
TROPICAL SYSTEM.


FORECASTER: MIKE HALPERT


NOTES: AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL 
PROBABILITIES) ARE NOW LABELED AS EC (EQUAL CHANCES).


THE NEXT MONTHLY OUTLOOK...FOR OCT ... WILL BE ISSUED ON THU SEP 16 2010


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1971-2000 BASE PERIOD.

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