1 Oct 2015

Hurricane Joaquin: to strike or not to strike US east coast?

Yesterday, I wrote a blog about the heavy rain that threatens eastern coastal states of the US in the next few days – this still stands.

However, I also mentioned the huge amount of uncertainty that lies with the path that Hurricane Joaquin will take this weekend and beyond.

This uncertainty still remains, with various computer models having different outcomes as to where the storm will go.


The overall theme is consistent, in that Hurricane Joaquin will head northwards from the Bahamas, but then the possible outcomes diverge.

Some computer models push it into the east coast of the US, whereas just as many push it out to sea over the Atlantic Ocean – see image below.

To strike or not to strike?

Hurricanes can sometimes be a struggle for weather computer models to handle, particularly when conditions in the upper part of the atmosphere are so finely balanced.

The path that hurricanes take is determined by something called the steering flow, which simply means which way the winds are blowing in the upper part of our atmosphere.

A key factor seems to be the position and orientation of a feature high up in the atmosphere called an upper trough.


Atmospheric football

The easiest way to imagine an upper trough is like a giant foot that dribbles and kicks weather systems around the atmosphere like a football.

It appears that the weather computer models are having difficulty in working out how this upper trough (foot) will kick Hurricane Joaquin (football) around.

If the base of the upper trough hits the hurricane, it would be the equivalent of kicking a ball with the toe of your foot – e.g. pushing it eastwards, away from the US.

However, if the upper trough digs under the hurricane, it would be like kicking a ball with your foot beneath it, which would then cause it to run up the bridge of your foot – e.g. pushing it westwards, towards the US.

What is likely to happen?

The latest runs of the weather computer models seem to be leaning more towards steering Hurricane Joaquin parallel or away from the east coast of the US.


However, the huge amount of uncertainty remains – so much so that hurricane surveillance aircraft will be making two missions a day around Hurricane Joaquin, to gather more data to feed into the computer models.

It is hoped that this will extra data will help the forecast to become clearer during the next 24 hours.

In the meantime, those living along the east coast of the US from the Carolinas to Maine will be keeping a close eye on each subsequent briefing from the National Hurricane Center.

I’ll be keeping an eye on the storm in the coming days and posting updates on Twitter – @liamdutton

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