It's an active week for typhoons and hurricanes in the northern hemisphere, which are the equivalent of tropical cyclones here in Australia. Typhoon Hato slammed into southern China on Wednesday, causing extensive flooding and wind damage in Hong Kong and Macau. The government broadcaster in Macau claimed that this was the strongest system to affect the region in almost 60 years. The typhoon also caused large waves and a storm surge as it made landfall, which exacerbated flooding along parts of the populated coast. The system was downgraded to a tropical storm after moving inland to the west of Hong Kong. Now, another system is threatening America and is likely to cause a prolonged period of severe weather in coming days. Hurricane Harvey is gaining strength over the Gulf of Mexico and is expected to make landfall over southern Texas, most likely on Saturday morning. The system could make landfall as a Major Hurricane, a category associated with one minute sustained winds in excess of 178km/h and capable of producing significant structural damages. Forecast models indicate that Hurricane Harvey may become slow-moving or stagnant after making landfall, which would compound the threat of flooding by causing a prolonged period of heavy rain. There is potential for more than half a metre of rain to accumulate in populated areas of southern Texas as the system continues to drag moisture-laden air in from the Gulf of Mexico for a number of days. There is also likely to be a significant storm surge as Harvey makes landfall, which will exacerbate flooding along the coastal zone. This will be most notable near and the the east of the hurricane, in the zone where winds will be blowing onshore. The future movement and development of Hurricane Harvey may change in coming days. Visit the http://www.nhc.noaa.gov/ for the latest track map and official warning information.