There was some serious concern that they wouldn't find another opportunity with good weather this summer. The Japan - Hawaii leg was the longest planned leg, and really stretched the aircraft's capabilities. If they couldn't find a good weather window in June (near the summer solstice), they faced ever shortening-days, and may have had to wait until next year for another attempt. They may have run out of funding during that year-long wait!

I'm glad they made it!