The archipelago of Hawaii has an exceptional climate. There are nearly 8 types of climates out of the 13 existing in the world! Quite incredible isn't it?
To understand this phenomenon, you have to look at the topography of the islands of the archipelago. But before explaining all this, let's take a general look at the weather, and what to expect once you're there.
1What's the weather like in Hawaii?
The Hawaiian archipelago is located in the North Pacific, slightly above the Tropic of Cancer. Its geographical location offers relatively pleasant temperatures all year round, varying between 18 and 32 degrees (65 to 90 degrees fahrenheit) on the coast, and an acceptable humidity level of around 60%, which does not make summers unbearable even though August and September are the hottest months.
Temperature differences between night and day vary little, but the thermometer generally drops below 25°C (75°F) at the coolest part of the night. As soon as you go up a little on the heights, the temperatures drop quickly, so that you can always find a little freshness.
It frequently snows on the summits of Big Island in winter, and this can exceptionally happen on the summit of Haleakala in Maui.
There are only two seasons in Hawaii. Summer from May to October and winter from November to April. Winter is milder and slightly wetter than summer. The months of December, January and February are reputed to be quite rainy but these are only generalities that are not always true, especially in the last few years when the weather offers more and more surprises...
For example, the month of April 2018 was very wet, causing severe landslides in Kauai.
Note that the hurricane season runs from June to November and can, depending on the year, bring momentarily a lot of rain. However, it is quite rare that the archipelago is hit by a hurricane.
More generally, you can expect to have rain all year round in Hawaii, even a little every day, in both summer and winter. The difference being that rainfall episodes are more frequent and longer in winter, whereas in summer it is more like a passing shower, sometimes only for a few minutes. Unless there is a major disturbance, the sun returns quickly, especially on windy coasts.
Be equipped accordingly! The sky can sometimes change in just a few minutes from a big blue sky to a deluge of rain.
This phenomenon can be explained by the important vegetation cover of the islands (except on Big Island where part of it is very arid). Unless there is a strong anticyclone, the daily evaporation has the effect of forming clouds throughout the day which pile up on the relief and wetlands, and come to discharge at the end of the morning. This is why the sky is often blue in the morning and becomes more charged during the day, ending in showers at the end of the afternoon. However, the wind can also change the situation. Finally, the most arid areas will be less exposed to the daily rains, like the tropical areas which, on the contrary, will very often be subject to rain, as for example the city of Hilo, the city where it rains the most in the USA: it rained 272 days in 2010.
Did you know that the mountain Waiʻaleʻale located in the heart of Kauai Island is one of the wettest places in the world! It rains on average each year the equivalent of 11.7 meters of water!!
Also, it is very likely that the weather will be very different from one end of the island to the other. Sometimes the weather can radically change on less than 10km! To understand why Hawaii's climate is so special you have to look at its topography.
Be careful of the floods!
One last thing to consider on the weather side is the risk of floods. Floods are sudden rises in river levels or the rapid flooding of roads that usually occur during heavy rainfall events.
But fortunately, Hawaii's weather services are on the alert and do not hesitate to warn the population if such a risk could occur.
In this case, you will receive a flood alert by message on your phone indicating the end time and place of vigilance. These messages are sent to all mobile phones in the area concerned.
If you receive such a message, don't panic, it's all about prevention! If you are at home, you are safe. If you are hiking, get to safety quickly. Finally, if you're on the road, be very careful when driving and avoid areas around bridges because rivers can overflow.
2Understanding Hawaii's weather and climate
The 4 main islands of Hawaii, Kauai, O'ahu, Maui and Big Island, all have peaks of varying heights. The youngest islands are the most mountainous: Maui with its volcano, the Haleakala, which rises to 3055 meters and Big Island with its two huge volcanoes, Mauna Kea and Mauna Loa, which exceed 4000 meters. On O'ahu and Kauai the peaks have been eroded by time, but beautiful ridges at over 1000 meters are still present.
These peaks form a barrier that blocks a good number of clouds that then gather on the eastern side of each relief.
This is why each island has a wet side and a dry side. The wetlands are exposed to the north and east of the islands. On the contrary, the areas to the west are much drier, except for Big Island where the southwest is often well watered, which is why there is a large market gardening area. Finally, the higher the peaks, the more the phenomenon is accentuated. For example, the driest area of the archipelago is north of Kona on Big Island because this area is located west of Mauna Kea, the highest peak of the islands.
The relief of these islands also contributes to create an important diversity of climates, which are mainly found on Big Island and Maui because of their high peaks. And the higher you go up the slopes of the volcanoes, the milder the climate becomes. That's why you'll find green meadows on the slopes of Big Island where it feels like you're in Ireland!
Thus, between the semi-desert, tropical zones, temperate zones and the summits where we cross a "tundra" type climate, we meet a total of 8 different types of climate just on Big Island!
To sum up, if we were to define a generality: the western and southern zones will be the sunniest but may see some rain in the evening. The eastern and northern zones will generally be very humid but may be clear in the event of wind or high pressure, especially along the coasts. As for the reliefs, they will very often be covered in cloud, especially from 10am onwards. Here too, it will be necessary to wait for a high pressure system or an episode of wind to see them clear even if the summits of Haleakala and Mauna Kea and Mauna Loa generally pierce above the clouds.
3When is the best time to go to Hawaii?
It is difficult to predict the weather, as trends are becoming less and less reliable. Nevertheless there are some points to know.
The summer months are logically the driest but the hurricane season from June to the end of November can bring its share of rain. The majority of years are very calm while others see hurricanes following one another as in 2018 where major storms and hurricanes have battered the archipelago throughout the summer.
If you want to avoid the heat of summer and thus the hurricane season, the months of April, May and June are the most pleasant and are generally not too rainy. October is also a good month but slightly warmer than spring. The advantage is that the ocean has a very pleasant temperature in this season, but we found the weather wetter than in spring. Finally July and August are very popular months for tourists (this is mainly due to school holidays), but the heat will be less pleasant than in spring.
Nevertheless it is difficult to give rules to follow because it is as much possible to have 2 weeks of good weather in December as 2 weeks of rain in April or July ...
As far as our feedback is concerned, we had a wonderful April in 2017, a rather changeable and rather wet October in 2018, September was also hot and humid in 2019 and October was rather nice. So far, April has been the most pleasant month for us, but when you see the torrential rains that fell in April 2018, you can still ask yourself questions!
So to choose the best period to come to Hawaii, we recommend you to orient your choice according to other factors (surfing, whales, snorkeling...) which will probably be more decisive than the weather aspect!