The Seagulls were beaten 4-0 at current champions Arsenal last time out, while the Hammers lost 2-0 to Tottenham Hotspur at the London Stadium, and Powell says both teams will be looking to raise their standards at the weekend.
She said, “West Ham have got lots of top-quality players that are very direct, and the loss against Tottenham means they’ve got a point to prove, as do we, in terms of needing to perform better.
“It’s going to be another tough challenge for us, but hopefully our support and the girls’ spirit will enable us to get something out of the game.
“There are no guarantees, but we want to do our best in what will be a very challenging game.”
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The match is Albion’s first outing after the international break, and Powell spoke of the difficulties of having a limited time to prepare for Sunday's fixture.
“It’s been challenging because we’ve had the international break, so those players that have been away for a week, and in some cases ten days, just returned on Thursday.
“It’s been a bit difficult to prepare, but I’m sure West Ham would say the same thing. We’ve only had Thursday and Friday to get ready for the game, but we’re excited by the prospect of playing again, especially after the bad result against Arsenal.
“It was bad in many ways in terms of the performance, and the way we lost. But the players are raring to go, to try and right some wrongs.”
The Albion manager also reiterated the importance of the club’s fans with four of the next five games taking place at home at The People's Pension Stadium in Crawley.
“It would be nice if we could get some momentum from having a run of games at home, and it’s great to see that our crowds are growing.
“We have in excess of 700 season-ticket holders, and sold another 300 tickets for this game. If they all turn up, then that’s a good figure turning up to support us.
“If we build up a few wins on the bounce, it will help us. The travelling to away games is tiring, so we’ve really got to take advantage of these home games.
“Our fans are really encouraging, and they get behind the girls. In turn, our players want to showcase themselves and almost say, ‘thank you for coming’ by trying to perform well. It definitely helps.”