What's Mrs. Figg doing in a raincoat?

I think there's a continuity error at the start of the film version of Harry Potter and the Order of the Phoenix.

Think about the opening sequences of that movie. It's a brutally hot, sunny day and Harry encounters Dudley and his gang in a local playground. A terrible storm suddenly develops, bringing howling winds, pouring rain and finally Dementors, which attack Harry and his cousin in the underpass leading from the playground back to their neighbourhood. It's a sudden, freak storm that no one could anticipate. So sudden and so freaky that Dudley automatically thinks Harry has created it.

Harry fights off the Dementors and, in a key plot point, old Mrs. Figg appears at the end of the tunnel in a rain coat, umbrella in hand, to help Harry home.

Are you with me?

We've got a sudden, freak storm on a broiling hot, sunny day. Yet somehow Mrs. Figg is dressed for rain when she arrives. Strange, isn't it? And I don't think you could argue she saw the storm brewing, put on her raincoat, then walked all the way to the underpass in the time available. She's too old and slow and the storm and attack both happened too quickly.

I think the filmmakers blew it.

Please note, in the book, Mrs. Figg arrives panting and in her slippers. One of her cats warned her that Harry was out and that Mundungus Fletcher had abandoned his guard duty. She immediately set off to find him and was as caught off guard by the storm and Dementor attack as Harry was.