The Models Trouble With LeslieAdded : Monday at 15:20 To understand why tropical systems prove so troublesome for global numerical models you need to understand two things... Energy and Resolution. It's these two things which combine to make remnants of tropical systems so inherently difficult to forecast. It's not unusual for global models to bring in remnants in one tun then discount it in another and this is why meteorologists tend to err on the side of caution until the systems are in the realms of the mesoscale models.
Here is Leslie today :-
Still thousands of miles away from the UK and over cooler water which is allowing her to weaken somewhat. By Wednesday and Leslie is expected to be here :-
Yup, hardly moved! Although Leslie has actually moved a little further South into warmer waters and the upper level shear drops somewhat which allows her to strengthen. What's amazing is the longevity of the system which first developed on the 23rd of September!
By T+78 and things are now developing. The main system is to the North of Leslie and this is a bog standard mid latitude low :-
Leslie at this point is caught up in the upper level steering and tries to hitch a ride on the jet stream. If it misses this, then (like yesterdays runs) Leslie heads towards Northwest Africa, but if it catches it then it runs in as a secondary low to the West of the UK.
Either scenarios are plausible and we wouldn't be foolish enough to go with either one until the system comes into the higher resolution European mesoscale models.
The reason for this is that tropical systems tend to be pretty small on a global forecasting scale. To try to model the complexity of all this energy within say a 468 3d grid pattern is nigh on impossible. But once the system comes into higher resolution modelling then the system can be broken up into over 20,000 3d grids which gives a better idea as to how the system is developing.
We expect Leslie to come into the European forecasting domain some time on Thursday, until then? Who knows...
METEOROLOGIST : MARSH |