You are on a hill with no trees on it, forty minutes into a queue that has not moved, holding a bottle you drank most of an hour ago. The stone underfoot is throwing heat back up at you. Somebody ahead has sat down on the kerb in a way that looks less like resting and more like giving up. It is twenty past two. The thing you came for is a hundred metres away behind a gate, and the honest truth is that you no longer want to see it — you want to be indoors, and you would trade the whole afternoon for a chair in a cold room.
The temperature did the damage, but the itinerary chose the hour. Somebody — you, a blog, a tour operator with a bus to fill — put an unshaded outdoor site in the middle of the afternoon in July, and every other decision that day was downstream of that one.
Heat is not like rain. Rain ruins an afternoon; heat can end a holiday, and occasionally it kills people, disproportionately the older ones. So this article is more practical than atmospheric. Which places actually get there, what the forecast number leaves out, and how to build a day with a hole in the middle of it on purpose.
Thirty-eight is a day, not a place
Start by dismantling the premise, because the research did. Of the cities below, only a handful have ordinary summer afternoons anywhere near 38C: Delhi, Dubai, Phoenix, Las Vegas, Marrakesh and — just — Seville. In Rome, Athens, Tokyo and Shanghai, 38C is not the climate. It is an event that lands on top of the climate, a few days at a time, and increasingly often.
That distinction matters because it changes the decision. You do not avoid Rome in July on the strength of its average; you go to Rome in July and keep a plan in your pocket for the three days that spike. Whereas Delhi in May is simply a different kind of trip, and pretending otherwise is how people end up in hospital.
Every figure here is a mean daily maximum for the hottest month, from the national meteorological service, at a named station — which matters more than it sounds. Athens ranges from 32.2C by the sea to 34.3C downtown depending on where the thermometer is, and Sydney's suburbs differ by more than that.
| City | When | What that actually means |
|---|---|---|
| Delhi | April to June | The pre-monsoon build. May averages a daily high of 41.2C at Ayanagar and June is barely cooler; the all-time high is 49.9C. |
| Dubai | June to September | August averages 42.1C, July 41.7C. This is the one place on the list where 38C would count as a mild afternoon. |
| Phoenix | June to September | July averages 41.4C. In 2023 the city ran thirty-one consecutive days at or above 43C, and reached it on fifty-four days in all. |
| Las Vegas | June to September | July averages 40.3C at Harry Reid, with a record of 48.9C. The dry air makes it more survivable than Delhi at the same number, not less serious. |
| Marrakesh | June to September | July averages 37.7C -- so an ordinary July afternoon sits right at the edge of this article. The record is 49.6C. |
| Seville | June to September | July averages 36.3C at the airport, and the city holds a 46.6C reading from July 1995. Andalusia is where a European summer stops being rhetorical. |
| Cairo | May to September | July averages 35.0C, which surprises people who expect worse -- but the record is 47.8C, and the heat arrives with no shade to speak of. |
| Athens | June to August | Downtown averages 34.3C in July and August. The metropolitan area also holds Europe’s highest officially recorded temperature, 48.0C at Elefsina and Tatoi in July 1977. |
| Rome | June to August | August averages 31.6C at Ciampino, with a 42.9C record. The normal Roman summer is hot; the heatwave Roman summer is a different city. |
| Istanbul | July to August | The Turkish met service puts the July and August mean daily maximum at 29.7C — modest on paper, except that almost every queue in the city is outdoors in direct sun. The record is 41.5C. |
| Shanghai | July to August | July averages 33.2C at Xujiahui with a 40.9C record -- and the humidity means the felt temperature runs well above the number. |
| Tokyo | July to September | August averages only 31.3C, which undersells it completely. Tokyo’s summer problem is humidity, not the thermometer. |
| Sydney | November to February | Two different cities fifteen kilometres apart. Sydney Airport averages 27.7C in January; Penrith in the western suburbs has hit 48.9C. |
| Bangkok | March to May -- not the summer holidays | The hottest month is April, averaging 35.7C, and Bangkok has never officially recorded 38C in July or August. Its problem is humidity in the mid-thirties. |
| Ho Chi Minh City | March to May | May peaks at 34.9C on average, and the July and August records sit below 38C entirely. Southeast Asia is not where you go to find a 38-degree day. |
The companion piece: how to plan a trip around rain →Read the full Tokyo guide →Read the full Shanghai guide →
The number on the forecast is a shade number
This is the single most useful fact in the article, and almost nobody is told it. The heat index — the “feels like” figure — is calculated for shade. The US National Weather Service puts the penalty for standing in full sunshine at up to 15F, which is around 8C. A forecast of 34C on an unshaded archaeological site is not a 34C experience, and no amount of stoicism closes that gap.
Humidity does something worse. Sweat only cools you when it evaporates, and humid air will not take it. The same service's own example: 36C air at 65 per cent humidity produces a heat index of 49C. That is why Tokyo's modest-looking 31.3C August average is misleading and Las Vegas's 40.3C is, in a strange way, more manageable.
And then the ground. The Arizona Burn Center measures outdoor surfaces reaching 82C in Phoenix summers, with asphalt running 20 to 30C hotter than the air — hot enough to cause contact burns in seconds. That is a warning about falls and about children and dogs, and it is also a plain physical fact about the environment you are walking through for six hours.
It is a band, not a moment
“Avoid the midday sun” is the advice everybody has heard, and taken literally it puts people back outside at three in the afternoon, which is worse than noon. Two different things peak at two different times. Ultraviolet peaks at solar noon, when your shadow is shortest. Air temperature peaks later, because the ground keeps absorbing more heat than it sheds for hours after the sun's highest point — the same lag that makes August hotter than June despite the longer June days.
So the dangerous stretch is a band running from late morning through mid-afternoon, which is the EPA's own phrasing, and the useful move is to treat it as a block of time that is spoken for. Not “we'll see how we feel”. Spoken for, in the plan, before you leave the hotel.
Four moves that actually work
Split the day in two, and mean it
The cities that live with this have already solved it, and they will tell you the answer if you read their opening hours. The Alhambra runs a summer timetable in two halves — morning until half past two, then again from five — and sells a Nasrid Palaces night visit from ten until half past eleven at night, at roughly half the daytime price. Greece goes further: during heatwaves the culture ministry has closed the Acropolis and other sites outright from midday to five, triggered at around 39C, as it did in June 2024 and again in July 2025. Two shifts, morning and evening, with a hole in the middle. Build the same shape yourself and the heat costs you almost nothing.
Book the cool hours like an appointment
The World Health Organization's guidance is not “stay hydrated”, or not only that. It is to spend two to three hours of the day somewhere genuinely cool, alongside about a cup of water an hour. Two to three hours is a museum, a long lunch, a bathhouse, a library, a cinema in a language you do not speak. Choose it in advance and put it in the day at the same status as the sightseeing, because a body that has not shed its heat load carries it into the evening.
Find out where the water is before you need it
Some cities hand it to you. Rome runs around 2,500 nasoni — the cast-iron street fountains — free and flowing around the clock, a couple of hundred of them inside the historic centre. Vienna claims 1,600 public drinking fountains, Paris about 1,300 with the locations published as open data, Zurich more than 1,200. In those cities a bottle and a map is a solved problem. Elsewhere it is not: in Cairo, Delhi, Marrakesh, Bangkok or Ho Chi Minh City the sensible default is that tap water is not for drinking, which turns hydration into a logistics question you should answer on the first morning rather than the fourth afternoon.
The waiting is the dangerous part
An air-conditioned train is not an air-conditioned journey. New York's subway platforms run as much as 11C hotter than the street — the trains' own cooling dumps its heat into the station — and readings around 36C have been recorded down there. London's deep tube lines have no air conditioning at all; only the shallower Circle, District, Hammersmith & City and Metropolitan lines do, with the first cooled Piccadilly trains not due until later in 2026. In Paris, lines 3, 8, 10 and 12 have no cooling of any kind. Plan the transfer, not just the route: five minutes on an open platform at half past three is the part of the day that hurts.
Four things you will be told that are wrong
Heat advice is repeated far more often than it is checked, and four pieces of it are actively unhelpful.
A fan will help
Only below about 40C. Above that, WHO is explicit that an electric fan blowing air hotter than your skin adds heat rather than removing it. In a heatwave, in a room with no air conditioning, the fan is a comfort object rather than a cooling one.
Thirty-five degrees wet-bulb is the limit of human survivability
This number is everywhere, and it was theoretical. When Penn State researchers actually put young, healthy people in a chamber, none of them reached it: in warm, humid conditions the measured critical value averaged closer to 30.6C. The real threshold is lower than the famous one, and lower again for anyone older or unwell — which is most of the people heat actually kills.
Just avoid midday
Taken literally this is the advice that sends people back outside at three in the afternoon, after the ultraviolet peak but into the temperature one. The hazard is the band, not the hour.
Southeast Asia is where the extreme heat is
Bangkok's hottest month is April, not August, and it has never officially recorded 38C in July or August. Ho Chi Minh City's July and August records sit below 38C entirely. Both cities are punishing in a different way — humidity in the mid-thirties, which the dry-heat tactics do not fix — and calling them 38-degree cities is simply wrong.
What PoppaTrip does with this, precisely
One narrow claim, so you can check it. The wizard asks how you feel about heat, with three answers: hardy, flexible, or avoid it. The planner treats any day whose forecast high reaches 33C as a heat day, and the scheduler then weights where things land on that day according to which of those three you chose — an “avoid it” answer pushes exposed stops away from the hot hours much harder than a “hardy” one does.
That is the whole of it. It does not know that the Alhambra opens again at five, and it will not stop you booking Delhi in May. What it does is stop your own preference from being quietly ignored by an itinerary that puts the unshaded hill at two in the afternoon.
Plan a trip that knows about the heat →The companion piece, for the other kind of weather →
None of this is about being careful for its own sake. It is about not spending the best week of your year queuing on a hot stone hill at two in the afternoon for something you could have seen at eight in the morning with nobody in front of you.
The cities that get a lot of heat worked this out generations ago and built their days around it. Copy them.