The following Class I areas are in the Hawaiian region:
Haleakala National Park
Hawaii Volcanoes National Park

A very good detailed climate description for Hawaii with a Hawaiian flare can be found at

http://www.wrcc.dri.edu/narratives/HAWAII.htm

Interested readers are encouraged to refer to this website. The following description of the climate of Hawaii is taken from that account.

CLIMATIC REGIONS OF HAWAII

It is convenient to recognize seven climatic sub regions in Hawaii. These are defined chiefly by the major physiographic features of the State and by location with reference to windward or leeward exposure. Since one region grades into another, it would be misleading to attempt to draw sharp boundaries between adjacent regions. In general, however, the regions and their characteristics are as follows:

(1) WINDWARD LOWLANDS, generally below 2,000 feet on the north to northeast sides of the islands. This region lies more or less perpendicular to the prevailing flow of the trade winds, and is moderately rainy, with frequent trade wind showers. Partly cloudy to cloudy days are common. Temperatures are more nearly uniform and mild than in other regions.

(2) LEEWARD LOWLANDS, except for the Kona coast of Hawaii which has a distinctive climate. In these areas daytime temperatures are slightly higher and nighttime temperatures are slightly lower than in windward locations. Dry weather prevails except for occasional light trade wind showers which drift over from the mountains to windward and for periods of major storms. In some leeward areas an afternoon sea breeze in common, especially in summer

(3) INTERIOR LOWLANDS, on Oahu and Maui. In the northeast these lowlands have the character of the windward lowlands; in the southwest, of leeward lowlands. The central areas are intermediate in character, and – especially on Oahu – are sometimes the scene of intense local afternoon showers from well-developed clouds which form as a result of local heating of the land during the day.

(4) THE KONA COAST OF HAWAII. This is the only region in the islands where summer rainfall exceeds winter rainfall. There is a marked diurnal wind regime, with well-developed and reliable land and sea breezes, especially in the summer. Summer is also the season with a high frequency of late afternoon or early evening showers. Conditions are somewhat warmer and decidedly drier than in windward locations.

(5) RAINY MOUNTAIN SLOPES ON LEEWARD SIDE. Rainfall and cloudiness are very high, with considerable rain both winter and summer. Temperatures are equable. Humidities are higher than in any other region.

(6) LOWER MOUNTAIN SLOPES ON LEEWARD SIDE. Rainfall is greater than on the adjacent leeward lowlands, but distinctly less than at the same level on the windward side except that the zone of maximum rainfall usually occurs just to leeward of the crests of the lower mountains. Temperature extremes are greater than on the rainy slopes of the windward sides of the mountains, and cloudiness is almost as great.

(7) HIGH MOUNTAINS. Above 2,000 or 3,000 feet on the high mountains of Mauna Kea, Mauna Loa, and Haleakala rainfall decreases rapidly with elevation. Near the summits of Mauna Loa and Mauna Kea, rainfall is scant and skies are clear a high percentage of the time. Relative humidities may reach values of ten percent of less. The lowest temperatures in the State are experienced in this region, with values below freezing being common.

THE CLIMATIC SETTING

The most prominent feature of the circulation of air across the tropical Pacific is the persistent trade-wind flow in a general east-to-west direction. In the central North Pacific the trade winds blow from the northeast quadrant, and represent the outflow of air from the great region of high pressure, the Pacific Anticyclone, whose typical location is well north and east of the Hawaiian Island Chain. The Pacific High, and with it the trade-wind zone, moves north and south with the sun, so that it reaches its northern-most position in the summer half-year. This brings the heart of the trade winds across Hawaii during the period May through September when the trades are prevalent 80 to 95 percent of the time. From October through April, Hawaii is located to the north of the heart of the trade winds. Nevertheless, the trades still blow across the islands much of the time, though with a frequency that has decreased to 50 to 80 percent in terms of average monthly values.

Besides the dominant trade winds, major storm systems may influence all parts of the islands, and in some areas there is a local exchange of air between land and sea on a rhythmic, diurnal basis. There is also the fundamental diurnal cycle of night and day. Because Hawaii is at a relatively low latitude with respect to the rest of the U.S., this cycle shows less variation in length than is found in any other state. Major storms occur most frequently between October and March, inclusive. During this period there may be two, three or even as many as six or seven major storm events in any particular year. Such storms typically bring heavy rains; and are sometimes accompanied by strong winds, at least on a local scale. The storms may be associated with the passage of a cold front – the leading edge of a mass of relatively cool air that is moving from west to east of from northwest to southeast. The storms may also be associated with a large eddy, or Low, that has been generated in the moving air in somewhat the same manner that an eddy is generated in a flowing river. Moist, warm air swirling into such eddies produces tremendous clouds and torrential rains.

Hawaiian land-and-sea circulations are on a far smaller scale than the circulations of the major storm systems. The exchange of air often is confined to areas of a few square miles or tens of square miles. Circulations of this kind are most common on south and west coasts, in locations that are to the leeward with reference to the trade winds and topographically sheltered from them. The Kona Coast of Hawaii, the Lahaina District of Maui, the Ewa-Waianae Coast of Oahu and the Barking Sands area of Kauai are among the localities in which these circulations are common. These circulations have a will-marked diurnal rhythm. Between forenoon and early evening air moves inland on a sea breeze. Sometimes these sea breezes are fairly brisk. During the night and until shortly after sunrise the sir drifts back from land to sea. The return drift is usually very gentle, so much that it can barely be felt.

There in only a slight variation in length of night and day from one part of Hawaii to another, since the major islands of the State all lie within a narrow latitude band. The variations at Honolulu are therefore generally representative of those of the State as a whole. The relatively constancy of the solar angle result in relatively small variations in the amount of incoming solar energy through the year.

The rugged configuration of the islands produces marked variations in conditions from one locality to another. Air swept inland on the trade winds of as part of storm circulations is shunted one way and another by the mountains and valleys and great open slopes. This complex three-dimensional flow of air results in striking differences from place to place in wind speed, cloudiness, and rainfall. Together with variations in the elevation of the land, it results in differences in air temperature. Thus the climatic pattern reflects not only such dynamic elements as the trade-wind flow, the passage of storms, and the seasonal rhythms of daylight and of solar heating, but also the static element of topography.

In general, the Hawaiian climatic is characterized by a two-season year, by mild and fairly uniform temperature conditions everywhere except at high elevations, by striking marked geographic differences n rainfall by generally humid conditions and high cloudiness except on the driest coasts and high elevations, and by a general dominance of trade-wind flow especially at elevations below a few thousand feet. How conditions differ in more detail from season to season and place to place is evident from the following summary, which treats specific aspects of the climate, discusses storms and other weather phenomena, and distinguishes among the principal kinds of climatic regions of the State.

TEMPERATURE

An outstanding feature of the climatic regime of Hawaii is the small annual temperature range, a consequence of the maritime influence. In downtown Honolulu the warmest month is August, with an average temperature of about 78° F the coldest, February, around 72° F – the range between the coldest and warmest months averages only 6° F. At Hilo the range is 5.0° F and at Lihue, 8.0° F. It seems likely that the range does not exceed 9° F at any location in Hawaii below and elevation of 5,000 feet. While annual temperature ranges are almost as small as this in a narrow zone bordering the coast of California, throughout virtually all the remainder of the United States they are very much larger.

Outside the dry, leeward areas, temperatures of 90° F and above are quite uncommon. In the leeward areas, temperatures in the low 90’s may be reached on several days during the year, but temperatures higher than these are unusual. At times the upper slopes of Mauna Kea and Mauna Loa are covered with snow during the winter. It is possible that under favorable circumstances cold air formed immediately above this snow cover on clear nights drains into local depressions and accumulates to sufficient depths to produce temperatures of 5° F or lower at the higher elevations. In exposed locations on the mountains, however, the cold air formed locally is often swept away and replaced by the far warmer air that is carried across and around the mountains by the upper winds; and the local winds that tend to move down slope at night and upslope during the day also have the effect of inhibiting the formation of extremely cold air. At elevations below 1,000 feet, the lowest nighttime temperatures on record have been in the 50’s, except in relatively cloudiness areas such as central Maui and the leeward coasts where temperatures in the high 40’s have been known to occur. Here again, these are extreme values, and it is possible for several years to pass before temperatures near 50° F are experienced in any locality near sea level. In general, lowland temperature conditions in all but the driest areas are well represented by the values for Honolulu, Hilo, and Lihue. Conditions in the driest areas are well represented by the values given later for Mana, Kauai; Waianae, Oahu; and Lahaina, Maui – all of which lie on leeward coasts in areas that are very dry and relatively free of clouds.

WIND

Over the ocean around Hawaii average wind speeds are highest during the summer trade-wind period. During the summer months (May through September) wind speeds over the ocean exceed 12 miles per hour 50 percent of the time. Eighty to 95 percent of the time these winds (except as disturbed by terrain) are from the northeast quadrant. During the winter (from October through April), when trade winds are not quite as prevalent, wind speeds are in excess of 12 miles per hour about 40 percent of the time. It is during this winter season that light variable winds are most frequent and this more than balances the fact that winter is also the time of occasional very strong winds – winds stronger than those experienced during the summer except with the rare occurrence of a tropical storm or hurricane in the summer period.

When the trade winds are moderate to strong – generally in excess of 14 miles per hour – they dominate the flow of air across wide reaches of the lowlands. In contrast, light trade winds are commonly felt only along the eastern to northern coasts of the islands and in exposed locations in the hills. With such light trades, there are often well defined local breezes along sheltered leeward coasts; and in some areas, as on the Kona Coast of Hawaii and in the Kihei area on Maui, these local sea and land breeze circulations occur not only when the overall wind is light but also when the trade winds are moderate to strong. Indeed, in these locations it appears that the local sea and land breezes may be reinforced by the trades.

Because wind conditions at any one time may vary from place to place, the frequencies at any one point are not representative of conditions everywhere in Hawaii. On a few exposed headlands and in mountain passes so oriented as to catch and concentrate the full force of the trades, winds above 40 MPH may occur several days each month of the year. In nearly all other locations, however, such winds occur only occasionally, and then only as the result of a major storm, the passage of a cold front, or an unusual local situation. Major high wind producing storms, discussed in a subsequent section, are chiefly events of the winter season

The Kula winds are strong down slope winds. They occur in the Kula District along a section of the lower slopes on the west side of Mt. Haleakala. According to observations by inhabitants of the area, the winds tend to be strongest in the zone that lies between 2,000 and 4,000 feet above mean sea level. In this zone there may be episodes of down slope winds with speeds of over 40 MPH as often as twice a year. However, winds with speeds n excess of 60 MPH probably occur only once every four or five years, on the average.

The Lahaina winds seem also to be down slope winds, but of somewhat different character from those of Kula. In the Lahaina area they have been given the name of “lehua winds” after the lehua tree which grows in that locality and with whose red blossoms the air is filled when these strong winds blow. They issue from the canyons at the base of the main mountain mass of western Maui, where the steeper canyon slopes meet the more gentle piedmont slope below. These winds have been reported from both the western and southern side of the western Maui mountains. They are evidently quite infrequent, occurring every eight to 12 years on the average. When they do occur, however, they are extremely violent, with wind speeds whose effects suggest they may reach 80 to 100 MPH or even more. They have been known to demolish buildings, uproot trees and cause severe lodging throughout whole fields of sugarcane. That they are partly down slope winds is evident from their being hot and dry. The mountains of western Maui are less than 6,000 feet high as contrasted with the 10,000-foot height of Haleakala, and it seems likely that these local Lahaina winds are caused, at least in part, by the funneling of strong trade winds through certain of the mountain gorges.

Aside from the more violent mountain winds, there are light to moderate mountain winds in many areas on the larger mountains of Hawaii and Maui and in a few local areas in the smaller mountains of the other islands of the State. The usual regime is to have upslope winds by day and down slope winds by night, and this circulation takes its place with that of the sea-and-land breezes in coastal locations as a finer, yet important, feature of the overall wind regime of Hawaii.

INVERSIONS

A. Marine Layer

Under trade-wind conditions, there is very often a pronounced moisture discontinuity at heights of between 4,000 and 8,000 feet. Below these heights the air is moist; above it is dry. The break occurs in association with a temperature inversion that is typically embedded in the moving trade-wind air, and represents a large-scale feature of the Pacific Anticyclone. From the surface up to the inversion, the temperature decreases with increasing height in a quite uniform manner. The moisture is well distributed throughout this lower layer, and the moisture content of the air is relatively high. At the base of the inversion the temperature increases by several degrees, sometimes quite suddenly. These higher temperatures may extend upward for several hundred feet before the temperature begins once more to decrease upward, in the manner that is most usual in the atmosphere. The significance of the inversion climatically is that it tends not only to produce a lower, more moist layer as against a higher, more dry layer, but it also tends to suppress the vertical movement of air and hence to restrict cloud development to the zone beneath the base of the inversion. When the inversion is present, as it is 50 to 70 percent of the time, its height fluctuates from day to day, but it is usually between 5,000 and 7,000 feet. It is significant in this regard that the trade-wind inversion, which tends to suppress vertical lifting of the air, is usually above the level of the crests of the low mountains and is never above the level of the crests of the high mountains.

The usual clarity of the air in the high mountains is associated with the low moisture content of the air. Except for occasional periods of a few hours duration, which seem to accompany the arrival of more moist air from below, the relative humidity is generally below 40 percent, and it often falls to 10 or even five percent. Such low humidities are characteristic of the zone above the inversion that separates the lower and upper air. Thus, except on the high mountains, the general regime in Hawaii is one of high humidity compared with conditions in most other states.

B. Local Inversions

e.g within the crater. To be prepared, if necessary.

RAINFALL

If the islands of the State of Hawaii did not exist, the average annual rainfall upon the water where the islands actually lie would be about 25 inches. Instead, the actual average is about 70 inches. Thus the islands extract from the air that passes across them about 45 inches of rainfall that otherwise would not fall. At Mt. Waialeale, on Kauai, the annual average reaches the extraordinary total of 486 inches – over 40 feet. This is the highest recorded annual average in the world.

There are very few areas elsewhere in the World and none elsewhere in the United States where rainfall gradients are as steep as they are in Hawaii. In a great many places in Hawaii the annual rainfall gradient exceeds 25 inches per mile; that is the rainfall increases 25 inches for each mile transversed along a straight line. In a very extreme instance, the gradient is 118 inches per mile along the 2-1/2 mile line from Hanalei Tunnel to My Waialeale on Kauai.

Seasonal/Diurnal Variations in Rainfall – Except for the Kona coast of Hawaii, at elevations below 2,000 feet throughout the State winter is the season of highest average rainfall. The Kona coast of Hawaii has a unique seasonal rainfall regime. Here, summers are wetter than the winters. The summer maximum on the Kona coast is associated with the facts that in the well-protected Kona coast is associated with the facts that in the well-protected Kona area, which lies to the leeward of Mauna Loa and Mauna Kea, there is a distinctive local circulation. Daytime onshore breezes yield fairly regular and sometimes in summer than winter. The winter storms that contribute the bulk of the average annual rainfall in other lowland regions of the State contribute less rain to the Kona coast.

In the lowlands at all times of the year, rainfall is most likely to occur during the nighttime or in the morning hours and least likely to occur during midafternoon. The more pronounced diurnal variations in summer is associated with the fact that most summer rainfall consists of trade-winds showers and these showers are most apt to occur at night. In winter most of the rainfall is the lowlands occurs in general storm situations, and these are as likely to take place during the daytime as at night.

STORMS

Most of the time the weather is dominated by the trade winds. Non-trade-wind conditions are quite different. When the winds are light and variable, moist air may move slowly onto the islands, typically from the southeast or south or southwest. Then there may be intense local storms, sometimes accompanies by lightning and thunder. These are usually small features that seldom cover more than a few square miles or less. There are four classes of disturbances that produce major storms. These four kinds of major disturbances are not always well defined, but are nonetheless convenient classes for descriptive purposes.

The first type, Cold Front Storms, occurs when a cold front sweeps across the islands bringing with it locally heavy showers and gusty winds. The second type is known as the Kona storm. This term was originally reserved for the slowly moving subtropical cyclones that occasionally enter the Hawaiian area, but is now increasingly applied by the local public to any widespread rainstorm accompanied by winds from a direction other than that of the trade winds. They include situations in which the low-pressure area is not well marked, but instead consists of a low-pressure trough into which air feeds from either side. The third class of disturbance is the true tropical storm or hurricane. These are rare, but may pass close enough to the islands to yield heavy rains, high winds, and great waves upon the coasts. Also meriting treatment as a separate and fourth class of disturbance are those instances of severe weather attributable to low pressure systems (Lows and troughs) in the upper atmosphere that are not associated with the foregoing cold fronts, Kona storms and tropical storms or hurricanes. Of particular interest are those which occur when the presence of trade winds in the lower atmosphere would appear to contraindicate the likelihood of extensive heavy rain.

These types of storms are described in more detail in the description at the website given at the beginning of this discussion.