We studied the temporal change in Zenith Total Delay (ZTD) from the GPS signals received at sites around the epicentral region of the 26 December 2004 Great Sumatra earthquake (Mw 9.0). The estimated ZTD values at the nearest GPS locations available around the earthquake region showed a significant rise after the earthquake at locations to its east (~63mm at NTUS) and south (~110mm at COCO), but no changes were seen towards the west. The increase in ZTD (and thus precipitable water vapor, PWV) associated to the earthquake process is attributed to the thermal energy released through the earthquake process and the probable heat induced on to the ocean surface through the magma upwelling processes in the earthquake region, which all might have caused increase in ocean water temperature and catalyzed the evaporation process yielding high precipitation over the region. However, this high precipitation did not produce rainfall in its vicinity and appears to have moved to the California coast by the subtropical jet stream present over the region during this period. The southern California experienced a historical heavy rain from 28 th of December, 2004 to 12 th of January, 2005 and the El Niño conditions in the Pacific Ocean alone could not explain such an unusual high precipitation in the winter period. We conclude that the severe weather conditions over the Californian coast and resulting flash flood might have been caused by transport of high water vapor formed over the Sumatra earthquake epicentral region to the California coast by the subtropical jet stream movement from west to east.