A SIT traveler’s choice of seasons & travel dates are usually personal preference unless defined by restricted vacation time, school opening/closing or host country’s seasonal events (Hue, Vietnam’s “Hue Festival  every 2 years in April).

    A. When to travel advice:
         1) probability of your ideal desired weather. Elaborate online resources available:                         

Source: Weatherspark: https://weatherspark.com/countries/s/JP/3#Figures-Temperature         

Nevertheless, weather is always a crap shoot

         2) avoidance of high-season’s ‘tourist’ congested chaos & inflated prices:  

              Anecdote: China: I scrambled during China’s 8 day New Year’s season to find a hostel bed because many Chines travel then & pre-book everything.

        3) avoid closure dates of site & activity. 

             Anecdote:  Antarctica: I traveled to Antarctica in March 2011 because  :
              a) I had 2 ½ months to kill after my Egyptian early departure & 
              b) Antarctica ship rates lowest at the end of their October to March cruising season 
              c) Antarctica is always cold anyway.

   B. Seasonal:

I typically chose travel dates based on the seasons. 
         1). If USA’s winter season, I purposely chose countries near the equator, e.g. Ecuador is on the equator, OR , in the southern hemisphere’s summer season, e.g., New Zealand, 

         Anecdote:  Arizona to Argentina: I left snowed covered Tucson, Arizona (a rarity) in the winter, arriving in Argentina's, Buenos Aires warm early fall like weather. Ironically, part of my travels were in Chili's northern Andes where it was chilly.

        2) In USA’s summer, I would chose countries in northern hemisphere e.g.Europe, China, etc. Occasionally  N & S Spain & Portugal

        3) A purposeful MIX of seasons:

        Anecdote: Camino de Santiago trek, Spain:

My late summer/early Fall Camino de Santiago trek had to anticipate August’s central Spain’s rainy/foggy rolling-hilled vineyards  

Then, Meseta Plateau’s chilly September early morning starts (6 am) & blistering treeless afternoons ..

ONTO the west Spain’s high plateau’s cold Fall mornings & lovely middays.           [ytlk: CdeS ]

       4) Late winter/early spring:  (???) so that I could minimize summers heat and avoid Summers tourist congestion.
                            Sometimes my clever 😇  planning worked. Sometimes it didn't. 

    Anecdote: Venice, Italy: I visited Venice in July suffering hordes of tourist and 2 solid weeks of rain. 

You can't win them all.         Sometimes I just went when I could.

Reflection: Rapid world wide tourism growth, particularly during summer vacation, is rendering major sites jammed with multi-tour buses & cruise ships disgorging 1000’s into snaking globs of tour groups often accompanied by the cacophony of multiple guide’s screaming megaphones.

     Note: Royal Caribbean’s new "Icon of the Seas" cruise ship carries 7600 people. Imagine the destructive  impact on tourist areas. Iconic (pun intended) example of the destruction of authentic tourism. 

More major sites are mandating, tourist, headphones to try to reduce chaos and try to restore, a worthwhile tourist experience.

   C. Site Chaos Avoidance tactics.

        1) Super popular Tier 1 sites.  
              a) choose off season travel, but before site closes for off-season, if they do. PIK: Coliseum

              b) Arrive well before 10 am & after 3:30pm when most tour & cruise folks leave. CAUTION: high tour, bus volume May force, tour bus, companies to arrive earlier or leave later

              c) During peak tourist hours, plan visits to small, obscure sites AND walkabouts outside the main tourists areas tourists tend not to go even when given free time.

        2) All sites:
              a) Arrive at or even before site opens: 

        Anecdote: Mexico’s Teotihuacan. (???)

             b) Some sites may offer early access tickets. Sometimes a little ‘baksheesh’ (mini-bribe) gets you in the door.

        Bus Tours/Cruises excursions have very INflexible scheduled site visits to profitably fulfill tourist package promises; a complex business model.