Louisiana bears brunt of Harvey’s remnants

There is some good news for the flood-hit states of the southern United States.

Tropical Depression Harvey, to give it its correct title, is now heading northeastwards, away from Texas and the lowest-lying parts of Louisiana.

It is also beginning to pick up speed, accelerating its move away from the region.

For much of the last week, whether as a hurricane or a tropical storm, Harvey has been moving at little more than walking pace.

Now that it is moving to the north of the subtropical high-pressure belt which had, in effect, marooned it, Harvey is picking up the pace. Its current speed is 14 kilometres per hour, which should soon take it into northern Mississippi and Tennessee.

Despite being downgraded to a depression, Harvey still has a notable circulation, and with a low-pressure centre of 998 millibars, there is still a storm surge risk for the Louisiana coastline.

Rainfall totals still give some cause for concern, not least because the rain bands are largely in the southwestern quadrant of Harvey’s circulation. Consequently, the heaviest rain is still in the extreme east of Texas and central and southern portions of Louisiana.

The National Hurricane Center, which, until now, has had the responsibility for forecasting Harvey’s progress, continues to warn of the risks of catastrophic and life-threatening flooding.

This is partly the result of the threat posed by the rain that has already fallen, especially as much of the floodwater is held back by bayous and reservoirs which are scarcely able to cope with the task. Concerns remain as to the consequences should these defences not be up to the task.

In the meantime, Harvey is expected to deposit another 75 to 300mm of rain across eastern Texas, Louisiana and Alabama. Further north into the Tennessee and Ohio valleys, there could be 50 to 100mm of rain which has the potential to cause some flooding problems, but nothing on the scale we have seen further south.

Harvey is the biggest rain storm to hit the contiguous US in recorded history.  The maximum rainfall was an astonishing 1318mm reported at Cedar Bayou, to the east of Houston. This more than one year’s worth of rain, falling in less than one week!

It is also worth noting that another cyclone may form in the Gulf of Mexico next week. This could threaten further heavy rain for some of the flood-hit areas, although forecasters are expecting nothing on the scale of Harvey.