Hurricanes Rarely Hit Hawaii

Hurricanes rarely hit Hawaii

By Jack Williams, USATODAY.com

The danger of a hurricane hitting Hawaii any single year is very low, but both meteorology and history tell you not to ignore the possibility, especially if you're building or buying a home there.

First the meteorology.

Hawaii is in the tropics and while the oceans around the state aren't as warm as those of the Caribbean Sea or Gulf of Mexico, the state does not have a chilly water barrier, like California's, which has helped keep any hurricanes from hitting that state — as far as anyone knows. (Related: California's tropical cyclones).

In addition, hurricanes and tropical storms approach Hawaii from both the east and the south, with storms that form in the eastern Pacific Ocean off the Mexican Coast being the most common. (Related: Understanding Eastern Pacific hurricanes)

The normal, east-to-west winds across the tropical Pacific push storms toward Hawaii, with a storm making it all of the way from time to time and many continuing west past Hawaii.

/ Storm that wouldn't die / /

From time to time, a hurricane sails past Hawaii to cross the International Date Line, which makes it a typhoon. In 1994, Hurricane John did even better.
It formed over the eastern Pacific and grew into a hurricane on Aug. 11, with winds reaching 170 mph at one time.
John weakened before hitting Johnson Island, south of Hawaii, where the U.S. Army destroys chemical weapons, but still did $15 million damage. All of the people on the island were evacuated before the storm hit.
John crossed the Date Line on Aug. 28, becoming Typhoon John. It then turned around and crossed back to the east side of the Date Line on Sept. 8, to become Hurricane John again. before dying on Sept. 31.
John covered a total of about 4,000 miles during its month as a storm.

Also, a few tropical storms and hurricane form south of Hawaii and head north toward the islands.

In fact, Hawaii's most devastating storm, Iniki in 1992, came from the south to pass directly over the Island of Kauai on Sept. 10-11, 1992 killing six people and doing $2.3 billion damage.

Which brings us to Hawaii's hurricane history.

Meteorologists have no doubt that hurricanes have been hitting Hawaii since the islands first pushed up from the bottom of the Pacific as volcanoes.

Hawaiians had stories of storms from before Europeans and Americans arrived, but none seemed to be as aboujt storms as fierce as those told of in the legends of the people who lived around the Caribbean Sea before the Arrival of Europeans in the New World's tropics in the 15th century.

In fact, even Weather Bureau meteorologists didn't realize until 1950 that some of the strong storms that hit Hawaii from time to time were tropical cyclones. (Hurricanes are tropical cyclones over the Atlantic Basin or the Pacific east of the International Date Line.)

Robert Simpson and his staff at the Weather Bureau (It's now the National Weather Service) office in Honolulu recognized that a storm spotted east of the islands on Aug. 12, 1950 was a tropical cyclone, not an extratropical storm. (Related: How tropical, extratropical storms differ)

They called it Hurricane Able because at the time forecasters used the World War II vintage international phonetic alphabet — Able, Baker, Charlie and so on — to name storms. This storm was later given the Hawaiian name Hiki.

Simpson went on to become a towering figure in hurricane research and forecasting.

He organized and ran the USA's and the world's first large hurricane research program, which continues today as the National Oceanic and Atmospheric Administration's Hurricane Research Division and to head the National Hurricane Center. He's the "Simpson" in the Saffir-Simpson hurricane damage scale. (Related: The Saffir-Simpson scale)

Before 1950, meteorologists hadn't seen the differences between Hawaii's tropical cyclones and the island's extratropical "Kona" storms, which hit during the winter. The late summer, fall hurricane season can overlap the Kona season.

Today, a bright eighth grader who has stayed awake during Earth science class could probably tell you many times which storms seen in satellite photos are tropical and which are extratropical cyclones.

Simpson, and his 1950s colleagues, of course didn't have satellite photos and, as far as that goes, hardly any data about storms over the ocean except readings radioed from unfortunate ships that happened to stumble into a high winds and towering waves.

Figuring out that "Able" was a hurricane was like putting together a jigsaw puzzle with many missing pieces.

Since 1950, two hurricanes, including Iniki, have hit Hawaii. Here, "hit" means the storm's center came ashore on one of the islands. Others have come close enough to bring 74 mph "hurricane force" winds and to cause serious damage and to kill a few people.

Hawaii's mountains can increase a hurricane's damage.

First, mountains enhance rain, whether the state's normal day-to-day rain or rain from a storm. Rainwater rushing down mountains causes floods and flash floods. (Related: Trade winds govern Hawaii's weather).

Sometimes a storm squeezes winds through valleys, making it speed up.

Finally, in the past, and surely in the future, huge waves kicked up by far-away storms crash against Hawaii's beaches to wash higher than normal waves or eat away sand.

The hurricanes to hit Hawaii were:

•Dot, August 1959. Meteorologists on Air Force hurricane hunter airplanes estimated Dot's winds as 150 mph or faster on Aug. 2, which makes it the strongest hurricane ever recorded in the Central Pacific. But the storm weakened by the time at hit Kauai the night of August 6 with sustained winds measured up to 81 mph. At the time, Kauai was mostly agricultural but damages were estimated at $6 million in 1959 dollars mostly to the sugar, macadamia nuts and pineapple crops.

•Iniki, September 1992. Iniki formed southeast of Hawaii and was heading toward the north when its eye went inland near Waimea on Kauai on Sept. 11 with peak, sustained winds estimated at 130 mph and gusts up to 160 mph. The fastest measured winds were just below 100 mph at Lihue. Iniki's winds caused widespread damage and storm surge and high waves did extensive damage on both Kauai and the Island of Oahu.

Other notable Hawaiian storms included:

•Nina, November 1957. After forming near Palmyra Island south of Hawaii, Nina headed north with its center coming within 120 miles of Kauai, but this was close enough for winds up to 92 mph to hit Kilauea Point, Kauai, and for heavy rain to cause serious floods. The fastest wind ever recorded at Honolulu International Airport — 65 mph — occurred during Nina. High surf on Kauai's southern shore accounted for most of the estimated $100,000 (in 1957 dollars) damage.

•Iwa, November 1982. Iwa, like Nina, formed south of Hawaii and moved north to brush Kauai. It didn't produce 74 mph or faster hurricane force winds at any weather station, but the wind at Lihue came very close, 73 mph. Even without hurricane-force winds, Iwa did an estimated $239 million damage, mostly to hotels, and other tourist facilities and the growing number of homes that were replacing farms. It also knocked out power across Oahu, the island where Honolulu is located.

•Estelle, July 1986. This storm come from the east, but was heading directly toward Hawaii when it was most intense — it then jogged to the south to miss the Big Island. Still, Estelle sent very large waves into beaches on the Big Island and Maui. Even though the storm's highest winds didn't hit Hawaii, the high waves did more than $2 million in damage.

Trade Winds, Inversions, and Orographic lifting are keys to understanding Hawaiian weather:

"Trade Winds" are steady winds that blow from the east throughout the tropics much of the year. North of the Equator, trades generally blow from the northeast (in the southern hemisphere, from the southeast). For
mariners, trades provide reliable means of transportation (at least for those mariners traveling by sail!). They also cause a huge influence on precipitation patterns in the Islands, making some tourist areas rainy jungles.

Warm, tropical air contains very large quantities of moisture, caused by rapid evaporation of water from the warm ocean waters. Whenever this warm, humid air rises, it cools (a simple fact of atmospheric physics that
occurs everywhere). And as air cools, its capacity for holding water vapor decreases. Warm air can hold a LOT more water vapor than colder air, and as the warm tropical air rises and cools (by about 5.5 degrees Fahrenheit
per thousand feet), it reaches the point where it can hold no more water vapor. Meteorologists call this "saturation." At that point, condensation occurs, which means clouds form and precipitation begins.

Orographic Lifting: Rising air, or "uplift," can occur for a lot of reasons, including tropical storms. But the most sudden, and significant, reason for air to rise is because of the influence of topography (mountains). Whenever tropical air encounters mountains (on an island or on the coast of a continent), it is forced to rise very quickly, resulting in clouds and rain (often very intense rain, especially where the mountains are sudden and steep). And
since trade winds are quite steady and reliable, the mountains that produce the uplift (on the east sides of the islands) are wet and cloudy much of the time (a wet fact not welcomed by Tourists!)

In the Hawaiian Islands, trade winds occur well over 50% of the time
throughout the year; in some periods, this figure exceeds 90%. Thus, the east sides of the islands experience rainy periods much of the time. As the rising air ascends, two things happen. First, there is nearly always an inversion, in Hawaii's case a "trade wind inversion," above which the air is rather dry; usually this occurs at about 5,000 feet, and most of the rainfall occurs below this height. Second, the process of condensation is so violent and so thorough that by the time the air reaches this level there is generally very little water available anymore. The result is moderate rain at the coastline, much heavier rain on the slopes above, and rather dry conditions on the tallest mountain peaks. In the Hawaiian Islands, the rainiest places are generally
about 3,000 feet above sea level. Nights are usually wetter than days, because the air is cooler to begin with.

As air reaches the crest, it begins to flow downward along the leeward side of the peaks. As air descends, it gets warmer, and its capacity to hold water vapor increases. Even if new moisture is brought in from below, the "relative humidity" of the leeward side air is quite low, causing the likelihood of rainfall to be much lower than on the east side. As a result, leeward (west) sides of tropical islands tend to be much drier than windward (east) sides; ie. the Poipu Beach area is much drier and sunnier than the Princeville area on Kauai.(See Map below). Such weather facts are very useful for Tourists to know!

Also, the higher mountains, above 6,000-8,000 feet, are arid and parched. Click below for a Big Island climate discussion, or continue to read detail about the Island of Kauai.

The Big Island Climate Discussion

..Island of Kaua'i Climate......

The island of Kauai is a deeply eroded extinct volcano (Mount Waialeale), and is the oldest of the major Hawaiian Islands. At its highest point, the island rises to about 5,000 feet, very near the typical trade wind inversion height. Trade winds bring clouds and rain to the eastern slopes, with the rain increasing dramatically at higher elevation. Lihue, on the eastern shore, receives about 40 inches of rain per year, heaviest in the winter
months. But on the slopes of Waialeale, rains are much heavier and more frequent. In winter, about seven times as much rain falls on the mountain than in Lihue (43 inches in an average December, versus 6 at sea level).
But in summer, when trade winds are steadiest, Lihue averages about 2 inches per month and Waialeale nearly 30 inches! For the year, Mt. Waialeale's average is between 350 and 400 inches of precipitation. Some
very wet years in the 1960s caused its annual average to be listed at 460 inches at one time, which made it the wettest measured spot on earth, but the current "official" average is below 400. Be that as it may, Waialeale
is one of the wettest places anywhere. The steady rain and lack of sun stunts the growth of the tropical vegetation, which form a full-on rain forest farther down the slopes.

Journey only 10 miles west, however, and you'll be in an area of generally clear skies, intense sun, and dry, almost desert-like weather. Western Kauai is a classic "rain shadow" area, with annual average rainfall in the 12-25 inch range (in some places, even lower than that).

Few Thunderstorms: One might expect that thunderstorms would occur frequently on Kauai, as they do in Florida and many other tropical and subtropical areas. However, Lihue only receives and average of three days a year with thunderstorms. The trade wind inversion is the biggest reason for this: thunderstorms require deep cloud development, or "convection," and the trade wind inversion keeps this from happening most of the time!

Interestingly, despite Waialeale's wetness it may not even be the wettest spot in Hawaii, let alone the world. On Oahu's northeast side, there are areas that may receive more than 400 inches per year, although there are
no rain gages to confirm this. Oregon State University's Spatial Climate Analysis Service is in the process of updating Hawaii's annual precipitation map, and preliminary estimates of Oahu's mountains suggest
tremendous rainfall.

11/14/2000: One of this site's Hawaiian readers recently noted that the Hawaiian State rainfall record for a 24 hour period occured on Kauai. This was an astonishing 38 inches during one torrential 24 hour period in 1958.

Additional notes from George Taylor:

Warm tropical air contain big quantities of moisture. Uplift (from mountains) causes the air to cool and release
its moisture (Orographic precipitation). Since the Trade Winds are steady, this happens day after day, month after month, resulting in tremendous annual rainfall totals. In fact, we suspect that areas in Northeast Oahu may be deluged with even more rain than Mt. Waialeale --but there are no rain gages on that part of Oahu.

Intense Desert in Hawaii-- read this!

Barking Sands (near Polihale Beach) gets a mere 8 inches of rainfall per year, mostly when the wind is blowing the other way (Kona Winds). This is because when air descends, it gets warmer and dries out. Thus there are huge, nearly unbelievable contrasts between wet upwind slopes of Kauai, and dry downwind areas like Waimea Canyon and Barking Sands.