Gay Hawaii Travel Guild

Hurricanes

Main article: List of Hawaii hurricanes

The hurricaneseason in the Hawaiian Islands is roughly from June through November, when hurricanes and tropical storms are most probable in the North Pacific. These storms tend to originate off the coast of Mexico (particularly the Baja California peninsula) and track west or northwest towards the islands.

True hurricanes are very rare in Hawaii, indicated by the fact that only four have affected the islands during a 63-year period. Tropical storms are more frequent. These are similar to hurricanes but with more modest winds, below 74 mph (119 km/h). Because weak tropical storms resemble some Kona storms in the winds and rains they produce, and because early records do not distinguish clearly between them, it has been difficult to estimate the average frequency of tropical storms. A tropical storm will pass sufficiently close to Hawaii every year or two to affect the weather in some part of the Islands. Unlike cold fronts and Kona storms, hurricanes and tropical storms are not limited to the winter season. They are most likely to occur during the last half of the year, from July through December.

Hawai‘i is protected by the vastness of the Pacific (i.e. the improbability of a direct hit); as storms cross the Pacific they tend to lose strength if they bear northward and encounter cooler water. It is thought that the topography of the highest islands (Haleakalā on Maui, Mauna Kea and Mauna Loa on the Big Island) may protect these islands, and certainly Kauaʻi has been hit more often in the last 50 years than the others.

Effect on trade winds

The top image above shows the winds around the Hawaiian Islands measured by the Seawinds instrument aboard QuikSCAT during August 1999. Trade winds blow from right to left in the image. The bottom image shows the ocean current formed by the islands' wake. Arrows indicate current direction and speed, while white contours show ocean temperatures. The warm water of the current generates winds which sustain the current for thousands of miles.

Despite being a tiny speck of land within the vast Pacific Ocean, the Hawaiian Islands have a surprising effect on ocean currents and circulation patterns over much of the Pacific. In the Northern Hemisphere, the trade winds blow from northeast to southwest, from North and South America toward Asia, between the equator and 30 degrees north latitude. Typically, the trade winds continue on an uninterrupted course across the Pacific — unless something gets in their way, like an island.

Hawaii's high mountain landscape presents a substantial obstacle in the path of the trade winds. The elevated topography blocks the airflow, effectively splitting the trade winds in two. This split causes a zone of weak winds, called a "wind wake," to form on the leeward side of the islands.

Aerodynamic theory indicates that an island wind wake effect should dissipate within a few hundred kilometers and not be felt in the western Pacific. However, the wind wake caused by the Hawaiian Islands extends 1,860 miles (3,000 km), which is roughly 10 times longer than any wake observed elsewhere. The long wake testifies to the strong interaction between the atmosphere and ocean, which has strong implications for global climate research. It helps researchers assess climate sensitivity, namely how much increase can be observed in the global mean temperature as carbon dioxide levels increase. It is also important for understanding natural climate variations, like El Niño.

There are number of reasons why this phenomenon has only been observed in Hawaii. First, because the ocean reacts slowly to fast-changing winds, the wind system must be steady to exert force on the ocean, as is the case with the trade winds. Second, the high mountain topography of Hawaiʻi provides a significant disturbance to the winds. Third, the Hawaiian Islands are large in horizontal scale, extending over four degrees in latitude. It is this active interaction between wind, ocean current, and temperature that creates this uniquely long wake west of Hawaiʻi.

In addition, the wind wake drives an eastward "counter current" that brings warm water 5,000 miles (8,000 km) from the Asian coast to Hawaiʻi. This warm water drives further changes in wind, allowing the island effect to extend far into the western Pacific. The counter current had been observed by oceanographers near the Hawaiian Islands years before the long wake was discovered, but they did not know what caused it.^[5]

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