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).

--
Liam (Milton Keynes)
http://physics.open.ac.uk/~lsteele/

On 25/06/2012 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).


.... Yes, it's been a real 'wanderer' hasn't it!

If you look through the various issues of the 'Discussions', you can see
the hair-tearing-out that's going on in Miami ....

http://www.nhc.noaa.gov/archive/2012.../175401.shtml?

It looks, to try and answer your question, that the problem lies with
the actual behaviour and model prognoses of various upper air features
(which govern the broader steering flow adjacent to the T/S) which vary
from run-to-run within one model, and equally frustrating, vary between
the various models. And of course the T/S itself has some influence on
the environment within which it is being steered ... and there are
doubts about the activity which feed back etc.

Incidentally, if this thing manages to slip across to the south of the
Panhandle, it is forecast by some models to really wind up ....

Martin.


--
West Moors / East Dorset
Lat: 50deg 49.25'N, Long: 01deg 53.05'W
Height (amsl): 17 m (56 feet)
COL category: C1 overall

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.

On Jun 25, 9:09*pm, Martin Rowley
wrote:
On 25/06/2012 20:22, Liam Steele wrote:

I've been looking at the forecast for TS Debby over the past few days,
Does anyone know what the problems have been in predicting this track?

I can't recall seeing one turn in the complete opposite direction before

If you look through the various issues of the 'Discussions', you can see
the hair-tearing-out that's going on in Miami ....

http://www.nhc.noaa.gov/archive/2012.../175401.shtml?

It looks, to try and answer your question, that the problem lies with
the actual behaviour and model prognoses of various upper air features
(which govern the broader steering flow adjacent to the T/S) which vary
from run-to-run within one model, and equally frustrating, vary between
the various models.

The key to that is the model run disagreements.

You may wsh to compre intervals with the larger events on he

6.1 NEAR THE EAST COAST OF KAMCHATKA, RUSSIA
5.3 OFF THE WEST COAST OF NORTHERN SUMATRA
5 FIJI REGION
5.1 ANDREANOF ISLANDS, ALEUTIAN IS., ALASKA
5.9 NORTHERN SUMATRA, INDONESIA
5.1 OFF THE EAST COAST OF HONSHU, JAPAN
5.1 SOUTH OF THE KERMADEC ISLANDS
6 MACQUARIE ISLAND REGION

Not included but just as important, are the consecutive smaller quakes
at the same epicentres whose incidence connotes or denote (whatever
the term has not been coined yet) marked changes in storm values
downwards.

HTH,BFLIWMFTWTLOY.