In this study, the minimum values of precipitation in heavy and extreme rainfalls are determined to be 42.8 and 84.2 mm, respectively, by applying the percentile index to the daily rainfall data of 8 meteorological stations during the years 2001 to 2015. Subsequently, 30% of the 612 rainy days were selected, where heavy and extreme rainfalls occurred in at least 3 out of 8 stations. Moreover, out of these, 13 days were selected considering more time and space distribution and 4 days were selected for synoptic analysis. Furthermore, the reanalysis data of some parameters such as sea level pressure, wind and geopotential height were extracted from the NOAA database at different pressure levels. The synoptic maps were then designed using the GrADS software and finally these were analyzed in terms of synoptic – dynamic.
The analysis of the maps shows that the occurrence of heavy and extreme rain in Bushehr province results from the establishment of a blocking system of Rex or Omega blocking type at 500hPa level, and the development of Sudan's low-pressure system in the southwest and western strip of Iran. The limitation of low pressure in the southwest of Iran by two high pressure centers, one from the north to the south of Iran, and the other from Europe to north Africa, creates a strong convergence area, and results in the dynamic climb of air and extreme rainfall in the north of the Persian Gulf. The results also indicate that the main sources of moisture are the Arabian Sea, the Oman Sea, the Red Sea, as well as the Persian Gulf, and in some cases the Mediterranean Sea.