The 26-year-old lost his grandmother, six cousins and an uncle in Typhoon Haiyan while other relatives are missing.
Day revealed his mother Dening, who was born in the Philippines, only found out about the death of her mother via Facebook and admits he enters this week's tournament with a heavy heart.
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"Being half-Australian and half-Filipino after something like that happens you tend to bend towards that way," Day said when asked if he feels like he'll be representing both countries.
"Like I said it's difficult and there is no way to explain the (feelings) that go out towards the people that have been affected by this.
"I feel sad for them and hopefully everything starts to move in the right direction over there.
"My heart goes out to everyone that's lost someone loved over there.
"We're still trying to look for some more people, some more relatives over there, so it's a tough situation right now."
Day will represent Australia alongside world number two Adam Scott who is coming off consecutive victories at the Australia PGA and Australian Masters.
Scott praised Day's courage after deciding to play despite his family tragedy.
"I was excited to play with Jason here, I think it is great that the top two Australians are here representing this week," Scott said.
"I've been here for the last couple of weeks and the way golf has gone down here for the last couple of weeks has been such a positive and I think every credit to Jason for sticking around this week in a tough time and wanting to play and represent Australia."
While they are on the same side in the teams event, Scott and Day will be rivals in the individual event under the revamped World Cup format.
"It's an interesting week with an individual thing and a teams thing and we are going to want to beat each other but we're both going to want to win," Scott said.
"So I don't really know how that sits but I think it would be really great for golf down here, which is hot at the moment, for us to get in the mix this week and hopefully have a lot of home crowd support."
Day understands the importance of the week for Australian golf and admits his partner will take some beating this week.
"I know this is a big week for us and for Australia, to really represent Australia well," Day said.
"I'm definitely looking forward to playing with Scotty, he is playing pretty hot right now so I have definitely got a good partner that is probably going to carry me along the way.
"Like he said, I don't know whether to love him or not if he beats me but we are both going to go out there and do our best.
"If that is good enough at the end of the week, it he wins I am going to be happy for him and if I win he is going to be happy for me."