Tropical Storm Fiona formed in the exact same area as Earl and is travelling on the exact same path as him – so how come one tropical depression becomes a major hurricane and the other a weak storm?

Well, it’s all to do with the first tropical depression – the one that became Hurricane Earl.

Earl had nothing but warm waters and perfect air conditions in front of him.  The warm waters fuelled his energy levels while the atmosphere he was moving through was kind to him, giving him the perfect conditions to rotate and grow.

Hurricane Earl – captured by Astronaut Douglas H Wheelock on the International Space Station.

Fiona, on the other hand, was a bit like taking a drink of cola from a can that’s been open for two days.  A little flat.

As Earl roars across the ocean his massive winds are churning up the seas – displacing the warm layer of water on top and dragging up cooler water to the surface.  Warm water is the life line for a hurricane.  Once the warmth has gone it’s like the shut off valve being activated – they die fairly quickly.

Fiona is following Earl’s trail almost exactly – and so the waters below her aren’t as warm, limiting the amount of energy.

On top of that she is following so closely behind Earl that she is being affected by his outflow – a bit like a taking off directly behind a 747 – very hard to get going with those jet engines firing back at you.

So unless Fiona stalls and has a chance to get her bearings – or she changes path – she will never reach the same status as Earl.

The tropical waves following Fiona may well be far enough behind her that conditions will have levelled out again for perfect storm development – time will tell.

– WeatherWatch.co.nz