Tokyo has something going on in every season, but some are more comfortable for travelling than others.
Mid to late Spring (March-April) is cooler which means its pleasant for getting around and the bonus is its cherry blossom season. It is worth going to see this at least once, with the city blanketed in pink and the locals out celebrating the revered flowers with picnic parties under the canopies. The whole city goes cherry blossom crazy, with seasonal sakura (cherry blossom) flavoured foods and drink on the menu across many hotels, bars and restaurants and cherry blossom decorations around the shops and streets. Its also a great time to visit the Japanese gardens in the city with their array of fresh spring flowers. The blossoms bloom at a different time each year so keep an eye on cherry blossom reports on the internet to time your visit perfectly. Just be aware that accommodation prices tend to go up around this time due to the popularity and avoid Golden Week in late April when there a numerous public holidays which means a lot more locals moving around the city. In May the weather is already warming up.
Summer means humidity and sometimes very hot days. June is not ideal as it tends to be the rainy season which means high humidity and lots of wet weather. You’ll be sticky travelling in July and August, but if you can brave it, it’s worth going to experience the numerous summer festivals, rooftop beer gardens and annual fireworks displays. The Sumida River Fireworks are the largest and can be viewed from multiple vantage pints around the river. It’s also the season for shaved ice-a traditional summer dessert. If you’re lucky you’ll find a traditional vendor with a cart shaving the ice by hand.
Fall/Autumn offers cooler weather again, but you’re under threat of typhoons in October. November is beautiful as the leaves begin to turn and Autumn leaf decorations go up around the city. From mid-November, Christmas ‘illuminations’ go up around the city, draping streets and buildings in beautiful lights. Don’t miss the annual Christmas Illumination at Tokyo Midtown in Roppongi, a spectacular annual light show. You’ll need to rug up but it’s worth it for the sights.
Winter is very cold, though rarely below zero, and is best avoided unless you’re visiting Tokyo as a side trip to a skiing holiday elsewhere in Japan.