Kayganda ng araw na ito! -This is a bit formal. Ang ganda ng araw na 'to!- This is usually used by native speakers when they're feeling lucky or just simply when they think it is a beautiful day. Or you might want to say "Ang ganda ng araw ko", which can be translated as "My day was beautiful", used by Filipinos when the day favors them.

What a wonderful day - Kahanga hangang araw / Napakagandang araw