From looking at the ITV news website, I'm guessing there are 3 weather hubs on a weekend covering all regions
Emma Jesson did Granada, Yorkshire x 2, Tyne Tees and Border
Helen Plint did Central x 2 and Wales
Philippa Drew did Meridian x 2 and Westcountry x 2
Where does Anglia, London and Channel fit in with this, there are no videos on their sites, and which regions are the 'hubs' based in (Emma Jesson will be at Granada)
Anglia and London are in the Central and Wales hub. They usually get Helen , James Wright or Amanda Houston doing the weekend weather.
Granada etc get Emma Jesson and Kerrie Gosney but on occasions Emma has done the Wales etc weekend hub
One weekend I noticed they swapped it over and London and Anglia had the same presenter as Meridian (Philipa Drew I think) whilst Wales, Westcountry and Central had Kate Haskell. Whether this was because none of the Wales/Central/London/Anglia hub presenters were available and as Kate does Westcountry sometimes it made sense for her to do Westcountry with Wales and Central?