AnalternativeindexfortheonsetofsummermonsoonovertheSouthChinaSea(SCS)hasbeendesignedbasedonthereanalysisdataoftheNationalCentersforEnvironmentalPrediction-NationalCenterforAtmosphericResearch(NCEP/NCAR).ItisfoundthatthedifferencebetweenthegeopotentialthicknessoverGuangzhouandManilacanbeusedasanalternativeindexfortheonsetofsummermonsoonovertheSCS.SincetheconvectiveheatingaltersthegeopotentialheightandthedistancebetweenGuangzhouandManilaisofsynopticscaleinthegeostraphicframework,theindexcanrepresentthestrengthofheatingandthefirstbarocliniccellovertheSCS.Bycomparisonbetweendifferentindices,itisfoundthatthesummermonsoononsetovertheSCScanbeascertainedbytheverticalzonalwindshearbetween200hPaand850hPa,thezonalwindat850hPa,theOLRanomaly,andthealternativeindexdefinedinthepresentpaper.Themeridionalwindshearbetween200hPaand850hPaalwaysappearsovertheSCSmuchearlierthanthezonalwindshearandcannotbeusedasanindexunderconsideration.