On year 2005, there exist 28 tropical Atlantic storms and Hurricanes according to the Saffir- Simpson scale. Among of these, there existed three outstanding huge Hurricanes, KATRINA, RITA and WILMA with surface wind more than 150 Knots. The present paper investigates the role played by the blocking system over the Northern Hemisphere on Hurricane KATRINA. The 6- hour and daily NCEP/NCAR Reanalysis data composites for the meteorological elements (surface Pressure, surface wind, precipitation rate and geopotential height at 500 hpa level) over the Northern Hemisphere for August 2005 has been used through this study. In addition to that, satellite images for Hurricane KATRINA and its hazards have been used. These datasets have been analyzed using of anomalies methodology. The results revealed that there existed a diffluent block persisted over Siberia and associated with a huge westerly air current aloft over the North America from 22 to 31 August 2005. Also, a strong westerlies air current aloft existed over the North Atlantic region. Splitting of westerlies occurred over the North Atlantic and it has two appreciable branches. First one goes toward the north and the second one to the south direction toward of the tropical Atlantic region. The splitting of main air current over the north Atlantic exist an unusual strong north east and easterly wind in the tropical Atlantic region. These unusual winds that caused by the blocking system in the Northern Hemisphere circulate, accelerate and control the track of Hurricane KATRINA from 23 to 31 August 2005. Whereas, analysis of the 10- day mean anomaly of the geopotential height at 500 hpa for the Northern Hemisphere for August month of 2005 year revealed that there is an outstanding positive anomalies more than + 200 m over the North America simultaneously with positive anomalies more than + 150 m over Siberia occurred only during the last 10 days of August 2005.