Temperatures in Tokyo will be at least 30 degrees, with the warm winds and moist air from the sea promising high humidity.
That poses a challenge for all athletes, especially those like Arnold who confesses she is hardly a sun-worshipper at the best of times.
"I don't like heat. I'm a pale person," says the 25-year-old, who had to prepare thoughtfully for her successful F46 world title defence at the World Para Athletics Championships in Dubai in November.
"I did some heat chamber work before going out to Dubai. That was me sitting in a form of glass house which creates its own humidity at Loughborough University.
"I got used to sitting in the heat, then you try saunas. I did six hour-long sessions and that helped. But I will need to do more training in that type of humidity for Tokyo, because it's going to be a lot worse."
In Dubai, the javelin final was held in the evening when the heat was not at its most fierce. It will be the same in Tokyo, although by 7.00pm when the action starts, the heat and humidity will still be a huge factor.
"We weren't in bright sunlight in Dubai, but it was still very warm and humid," says Arnold, who believes Games organisers could still take some very simple and sensible steps to reduce the dangers for athletes.
"I understand that moving things around for organisers is sometimes difficult. But in Dubai I was out there for nearly two hours and in the end the heat got to me. I felt completely drained.
"Going back to my first world championships in Lyon in 2013, it was boiling hot - 39 degrees at 11 o'clock in the morning and there was no shade or shelter from the sun.
"Even in Dubai, we had chairs, but there was no shade for the athletes - not even in the morning when the sun was out.
"I trained for 10 years to win my first para event and you don't want that opportunity on the day to suddenly be undermined by the heat."
Arnold - who was born without a right-hand and forearm - will at least take with her the confidence that in 2019 she was still unquestionably the best female Paralympic javelin thrower on the planet.
She may have lost her world record to rival Holly Robinson of New Zealand last April, but when it mattered most at the throwing line in Dubai, it was the Team Wales member of 2018 who triumphed.
She admits that a lack of meaningful competition between events sometimes threatens to undermine her motivation, but she still delivers on the big occasion.
"I really struggled this year with trying to keep my motivation for so long. Having such a long gap from 2018 in the Gold Coast, to the Europeans, which were in July, was very difficult. There were no major competitions, really for 18 months, until I competed in Dubai.
"Because of how late in the year it was, I only had three competitions before going to Dubai. My main goal was to go out there and defend my title. A fourth consecutive title was what I really wanted.
"A lot of people talked about breaking records, but my mindset was just to go out there and take the gold medal home.
"If anything else came after that, I would have been really happy. But I ended up with a personal best, which is pretty amazing in November with only a couple of competitions beforehand to test me.
"So, I was really happy with my performance. I am my worst critic, so I was happy with how I competed. But there is always lots more to come."
If Arnold wins again in Tokyo, she will be a double Paralympic champion and four-time world champion in her mid-twenties.
It would be a remarkable era of dominance, but she has no plans to walk away just yet and after a period of walking, swimming, badminton and yoga back at her Grimsby home at the end of last year, she is ready to pick up her spear again and start chucking.
"I will be 26 in June," she says. "The future is always in the back of my mind because competing in sport is not for life.
"You need a back-up plan. I have thought about staying in sport - whether that's coaching or media - but I've not made any firm decisions yet. I started when I was 14, so I think I've got plenty of knowledge to give.
"But I'm not a planner. I don't like to plan years ahead. I like to live every day as it is, but with a big goal within the year ahead.
"Things happen and you have to live life in the present. When I feel I don't love competing any more then that will be my time to retire, but it's certainly not happened yet."