Industry insiders Jeff Grubb and Mike Minotti have claimed that a Nintendo Direct is scheduled to take place at some point in September and could happen "as soon as next week."
Grubb and Minotti share this information on their Last of the Nintendogs podcast (thanks, GamesRadar), in which Grubb says a Nintendo Direct could take place next week, but is more confident it will actually happen during the week starting September 12. Both Minotti and Grubb claim that they are "very, very sure" that ports for both Twilight Princess and Wind Waker HD will be announced during the Direct.
Grubb also believes that Nintendo is planning to make this Direct a "Zelda blowout," speculating that Nintendo may announce the ports to tide fans over until the release of Breath of the Wild 2 in 2023. Both insiders also speculate that we may actually get an official title for Breath of the Wild 2 during the event, as well as possibly a Metroid Prime remaster announcement and a new release date for Advance Wars 1+2: Re-Boot Camp.
However, it's worth noting that everything besides the Wind Waker and Twilight Princess ports is pure speculation from both Minotti and Grubb, and Grubb himself is unsure of just what the Direct will entail. There seems to be confusion over whether it will be a General one or just a mini, but it likely isn't a Partner Direct since Zelda announcements will apparently be made there. Grubb does state that third-party games will be announced during the event, although claims that none of the announcements he's heard about are "super exciting."
While none of this has been confirmed by Nintendo just yet, it does track with the company's history of Direct announcements. Nintendo hasn't gone without a Direct in the month of September since the Switch's release, so it does stand to reason that there'll be one this year as well. Whether it will include the announcement of Wind Waker and Twilight Princess ports, we'll have to wait and see.