Hi,

There is a covered walkway from the JR Shinjuku covering most of the way to the Hyatt Regency Tokyo Shinjuku so less to worry about in the heat. As mentioned above staying at the HR Tokyo bay and sightseeing in Tokyo with the travel will get old quickly ( ie no opportunity to come back to the hotel during the day to relax. We stayed at the Hilton Tokyo Bay for a few days and went into tokyo to sightsee ( after a day sightseeing and back to the hotel we just stayed there at night) . At more central hotels, we found it easy to explore in the morning, back to the hotel in mid afternoon, relax, have dinner then go out again in the evening to see some of the night sights. I personally like to come back to the hotel mid afternoon ( up early then sightseeing) to relax ( pool if they have one) then go out again in the evening

Regards

TBS