Hurricane Harvey slams into the Texas coast

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  • Hurricane Harvey over Texas on Saturday at 2pm, local UK time.

  • Hurricane Harvey slams into the Texas coast
    26.08.2017 13:30

    The much-anticipated land-fall of Hurricane Harvey took place at 10pm local time on Friday 25th August. It arrived on the coast as a category 4 storm. Hurricane strength is measured on the Saffir-Simpson scale where 1 denotes the least-strong hurricanes and 5 the strongest. Hurricanes develop their deadly strength from the energy derived from the warm sea surface. Once over land, they weaken. Harvey was downgraded to a Category 1 storm on Saturday morning. Winds that had been gusting to 130mph at the time of land-fall at Rockport, Texas, had eased to 80mph over the following 12 hours.  It is already classed as the strongest hurricane since Wilma hit Florida in 2005.

    Texas is going to have to deal with the effects of Harvey for days and weeks to come. The storm-surge rise in sea level is expected to reach 13 feet along the low-lying coast. The greatest catastrophe is expected to be the huge rainfall expected. Why?  Although the rotating winds are very strong, the storm itself is hardly moving, it was moving inland at just 8mph on Saturday. Over the next few days it is expected to meander around without much further inland progress, probably edging eastwards towards Louisiana. In the first 6-hours after land-fall, south-east Texas had recorded around 250mm of rain. Over the next few days, sustained rainfall from this storm could give rainfall totals of 700-900mm. This is the equivalent of well over a year’s average rainfall in London and eastern England!  The area expected to receive more than 500mm of rain includes the city of Houston.

    The reason the risk of flooding is so high is that when a hurricane strikes a coast at right angles (Harvey was moving north-west when it struck the coast) it tends to slow down as it loses energy. In the case of Harvey, it is quite possible that the storm will then meander back to the Gulf coast and then move slowly back inland a little further east, basically concentrating the rainfall in a very small area. By contrast, most of the hurricanes that strike the USA tend to hit the east coast at an oblique angle, running along the coast, this spreading the rain more widely. 

    The influence of global warming on tropical cyclone frequency (a hurricane is simply a tropical cyclone that forms over the Atlantic) is much debated. While there is a clear link to sea surface temperature, some research has suggested that rather than giving a greater number of storms, warming will just increase the risk of a storm becoming intense. Past records of Atlantic hurricane frequency are problematic. While there has been a rise in frequency since the 1990s, there is no evidence of a longer-term upwards trend. There are also concerns regarding our ability to observe hurricane frequency in previous decades. One thing we can control is the rise in population along hurricane-prone coasts and the preparedness of local inhabitants.

    By: Julian Mayes