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Climate - Hawaii


Average weather, temperature, rainfall, sunshine

Flag - Hawaii

Map - Hawaii

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In Hawaii, the climate is tropical, with a hot season from June to October (called kau in the Hawaiian language) and a relatively cool season (hooilo) from December to March. The trade winds, constant winds blowing from the north-east, strongly influence the climate of these islands, creating microclimates, wet or dry, depending on slope exposure.

Index


  • The coasts - Honolulu, Hilo
  • The mountains - Mauna Kea, Mauna Loa
  • Cyclones

The coasts



Temperatures in Hawaii vary little throughout the year; they tend to be a bit lower on the windward slopes, and a little higher, but with lower humidity, on the leeward slopes. The temperatures vary little also when compared with the averages. This happens both because of the location at tropical latitudes and because of the enormous distance from the continents, from which cold or hot air masses could arrive. At sea level, the highest recorded temperatures are about 35 °C (95 °F), while the lowest are about 11 °C (52 °F).
Rainfall is influenced by the trade winds, so it varies according to slope orientation: you can move from a forest to a desert in a few kilometers (or miles), just by climbing over a hill.
In the following map, we can see a scheme of the situation, relative to the island of O'ahu: the trade winds bring rainfall on the exposed slopes and hot and dry weather on the leeward slopes. This situation also occurs on other islands where elevations are found in the interior, while flat islands such as Ni'ihau and Kaho'olawe are entirely arid.

Trade winds on the island of O'ahu

Honolulu

Climate chart - Honolulu
In the capital, Honolulu, located on the southern side of the island of O'ahu, the daytime temperature ranges from 27 °C (81 °F) between January and March to 30.5/31.5 °C (87/89 °F) between June and October. Being on the leeward side, where the trade winds create a sort of slight down-slope, foehn-type effect, Honolulu is one of the warmest places in Hawaii. Here are the average temperatures.
Honolulu - Average temperatures (1991-2020)
MonthMin (°C)Max (°C)Mean (°C)Min (°F)Max (°F)Mean (°F)
January192723.1678073.6
February192723.2678073.8
March202723.7688174.6
April212824.8708376.6
May222925.6728578.2
June233126.9748780.4
July243127.6758881.6
August243227.9768982.2
September243127.6758881.6
October233126.9748780.4
November222925.5728477.9
December212824.2698275.5
Year21.929.225.5571.584.678

Rainfall on the leeward side is generally lower than 1,000 mm (40 in) per year, with a minimum from May to September and a maximum from December to March: in practice, it rains almost only in winter, when the clash between air masses can produce wet currents from the southwest, while in summer, the rare downpours only occur when the strongest thunderstorms produced by the trade winds on the other side manage to pass over the mountain ridges.
At the Honolulu airport, located on the coast, only 415 mm (16.4 in) of rain fall per year, with a maximum from November to March and a minimum from April to September. However, the amount varies according to district: at the university, located near the green hills overlooking the city, it reaches 1,000 mm (40 in) per year, with more abundant rains from November to March, and some extra showers also in summer.
Here is the average precipitation at the international airport.
Honolulu - Average precipitation
MonthMillimetersInchesDays
January451.88
February5028
March602.49
April200.88
May200.86
June150.66
July150.67
August200.86
September200.87
October401.68
November552.29
December552.29
Year41516.389

The amount of sunshine in Honolulu is never poor: it is acceptable from November to January and good or very good in the rest of the year, when the sun usually shines. Here are the average sunshine hours per day.
Honolulu - Sunshine hours
MonthAverageTotal
January7215
February7.5215
March8.5260
April8.5250
May9280
June9.5285
July10305
August10305
September9.5280
October8245
November6.5200
December6.5200
Year8.33035

Hilo

Climate chart - Hilo
On the coasts exposed to the north-east, which directly receive the wind from the sea, the temperatures are a bit lower. Here are the average temperatures of Hilo, located at the foot of the windward side of the island of Hawai'i ("The Big Island"): as we can see, they are lower than those of Honolulu, which, as previously mentioned, is located on the leeward side.
Hilo - Average temperatures (1991-2020)
MonthMin (°C)Max (°C)Mean (°C)Min (°F)Max (°F)Mean (°F)
January182621.8647971.3
February182621.8647871.2
March182622.1657871.8
April192622.5667972.5
May202723.4678174
June202824698275.3
July212824.6708376.4
August212824.8708376.6
September212824.8708376.6
October212824.3698275.7
November202723.3688073.9
December192622.4667972.2
Year19.62723.367.380.674

In addition, on the northeast-facing slopes, it rains all year round, and the climate can be defined as equatorial. In Hilo, 3,050 millimeters (120 inches) of rain fall per year, without there being a dry month: May is the "driest" month with 180 mm (7.3 in) of rain, while the rainiest is November, with 365 mm (14.3 in). Here is the average precipitation in Hilo.
Hilo - Average precipitation
MonthMillimetersInchesDays
January2007.916
February26010.217
March32012.622
April2409.424
May1807.123
June1857.325
July2359.327
August28511.227
September2208.723
October26010.223
November36514.423
December3051222
Year3060120.5273

Because of frequent clouds and rains, the sun does not shine very often on the windward side, as can be seen in the following table.
Hilo - Sunshine hours
MonthAverageTotal
January5160
February5.5150
March5155
April4.5135
May5155
June6175
July5.5165
August5.5175
September5.5160
October4.5135
November4115
December4130
Year51815

On the coasts exposed to the wind, higher waves are also formed, so surfers flock to beaches facing north, such as Sprecksville and Ho'okipa Beach on Maui Island.

Hookipa Cove

The sea in Hawaii is warm enough to swim in all year round, even though it drops to 24.5 °C (76 °F) in February and March, as can be seen in the following table, concerning the water temperature on the southern island of Hawai'i.
Hilo - Sea temperature
MonthCelsius (°C)Fahrenheit (°F)
January2577
February2476
March2476
April2576
May2577
June2678
July2679
August2680
September2780
October2780
November2679
December2578
Year25.577.9

The mountains



Hawaii are volcanic islands. The highest volcanoes are found on the island of Hawai'i, and are Mauna Kea, 4,205 meters (13,796 feet) and Mauna Loa, 4,169 meters (13,679 ft). On the island of Maui, we find Haleakala (or East Maui Volcano), 3,055 meters (10,023 ft) high. On the other main islands, there are lower volcanoes.
Obviously, the temperature in the mountains decreases with altitude. Here too, precipitation is more abundant on the slopes exposed to the trade winds than on the leeward ones; moreover, they are more abundant at intermediate levels, since the trade winds only blow from sea level to about 1,800 meters (5,900 ft). So on the highest mountains, above a certain altitude, a mountain desert is found, which becomes cold above 3,000 meters (9,800 ft).

Mauna Kea

At the Mauna Kea Observatory, at 4,200 meters (13,800 feet) above sea level, the average temperature in the coldest months is around freezing; however, at night, it can drop below freezing all year round. The lowest record is -11 °C (12 °F), but since the average minimum of January and February is -3 °C (27 °F), even in this case, the record does not differ too much from the average.
Here are the average temperatures of the Mauna Kea Observatory.
Mauna Kea - Average temperatures
MonthMin (°C)Max (°C)Mean (°C)Min (°F)Max (°F)Mean (°F)
January-361.5274334.7
February-361.5274334.7
March-450.5254132.9
April-351274133.8
May-293.5284838.3
June-1104.5305040.1
July-1115305241
August-1104.5305040.1
September0105325041
October-173304537.4
November-272.5284536.5
December-262284335.6
Year-1.97.72.928.645.837

At this altitude, precipitation is very scarce: just 190 mm (7.4 inches) per year, with a maximum of 25 mm (1 inch) in March and November. However, above 4,000 meters (13,000 ft), during some winters, you can see the snow on both Mauna Kea and Mauna Loa.

Mauna Loa

Climate chart - Mauna Loa
At the Mauna Loa Observatory, located not in the summit but on the northern slope of the volcano of the same name, at 3,400 meters (11,100 ft) above sea level, the temperature is a bit higher, but still quite cold, especially in winter.
Mauna Loa - Average temperatures (1991-2020)
MonthMin (°C)Max (°C)Mean (°C)Min (°F)Max (°F)Mean (°F)
January2116.2355143.2
February1105.7345042.2
March2105.9355142.7
April2127.1365344.8
May4138.6395647.4
June5149.6415849.4
July5149.5415849.1
August5149.4415749
September5149.2415648.6
October4138.7405647.7
November3117.1375244.8
December2116.4365143.4
Year3.312.37.83854.146

At the Mauna Loa Observatory, precipitation amounts to 365 mm (14.4 in) per year, so it is quite scarce, but not at desert levels as on the summit.
Mauna Loa - Average precipitation
MonthMillimetersInchesDays
January301.24
February2516
March5027
April200.84
May150.64
June100.42
July301.24
August602.46
September150.65
October351.45
November301.25
December351.46
Year36514.456

Mauna Loa Observatory

At lower elevations, around 2,000 meters (6,500 feet), in winter, the night temperature can sometimes drop below freezing (0 °C or 32 °F), while the air becomes mild during the day, as we can see from the averages of the Pohakuloa Training Area, located on the plateau between the two volcanoes, at 1,900 meters (6,200 ft) above sea level.
Pohakuloa - Average temperatures
MonthMin (°C)Max (°C)Mean (°C)Min (°F)Max (°F)Mean (°F)
January41911.5396652.7
February31810.5376450.9
March51912416653.6
April61912.5436654.5
May62013436855.4
June62113.5437056.3
July82215467259
August82215467259
September72214.5457258.1
October72114457057.2
November72114457057.2
December51912416653.6
Year620.313.142.868.555.5

As we said before, on the windward slopes, it rains often at low altitudes, but at intermediate altitudes, it rains almost every day. For example, at the top of Mount Wai'ale'ale, 1,500 meters (5,000 feet) above sea level, on the island of Kaua'i, 9,500 mm (374 in) of rain fall per year (according to other sources, the amount is as high as 11,500 mm or 453 in), which makes it one of the rainiest places in the world. The windward slopes of Mount Haleakala are very rainy as well, so much so that rainfall exceeds 6,000 mm (235 in) per year.

Tropical cyclones



In theory, the Hawaiis are in the path of tropical cyclones, but as a matter of fact, they are rarely affected by them. The cyclone season runs from June to November, although the islands have historically almost never been affected before July; however, they are most likely in August and September. The most intense hurricanes in the islands' history have been Dot in August 1959, Iwa in November 1982, and Iniki in September 1992. Since hurricanes often weaken as they approach Hawaii, to the point that the effects they bring are usually not too serious, such as waves and wind, it has been assumed that they are protected by their very high volcanoes, which could disturb the spiral structure of cyclones.

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