On 25/06/12 20:22, Liam Steele wrote:
I've been looking at the forecast for TS Debby over the past few days,
and it's interesting how the forecast has changed.

After gaining TS status, Debby was predicted to move westwards towards
Texas, eventually reaching hurricane-strength. This track was
subsequently altered over the next few days, and when I looked yesterday
Debby was instead predicted to move northwards towards Alabama. I've
just looked now, and the track has changed to eastwards, moving over
Florida.

Does anyone know what the problems have been in predicting this storm
track? I know from previous years that paths are constantly amended, but
I can't recall seeing one turn in the complete opposite direction before
(though admittedly I have only been viewing the path predictions for a
short while).


It is because the steering currents are very weak, which is causing the
TC to move very slowly and erratically. The forecast motion will be
determined by the forecast position of upper level troughs and ridges,
sometimes just a slight change in these steering features can mean the
difference between a TC being picked up by a trough and accelerating
away, or the trough passing by and the TC stuck in a slack steering flow.