Hawaii -- Often Protected From Hurricanes

Hawaii, although potentially in the sights of Tropical Storm Erick, rarely sees hurricanes and tropical storms.

While this may seem a bit strange at first, considering the Islands` tropical location. However, a protective shield of colder water and strong upper-level winds keep most storms at bay. That said, the Aloha State is not immune to hurricanes, and remains exposed to storms that arrive from the south.

In general, hurricanes and tropical storms thrive on the warm water of the tropics, with sea-surface temperatures of 80 degrees typically needed to maintain a hurricane`s strength. During the summer months, Pacific water temperatures this warm are found along the Mexican and Central American coast as far north as southern Baja California. But further off the coast, the deep Pacific Ocean circulates cooler water up to reach the surface in a process known as "upwelling." Hawaii is located on the edge of one of these deep ocean trenches which stretches for about 1,000 miles to the east, and as a result some of the water off of the Hawaiian Islands is as warm as the upper 70s near Hawaii. While these water temperatures are comfortable for swimming, they are poison to most hurricanes.

Generally speaking, a hurricane or tropical storm will travel east-to-west, directed by the tropical trade winds. However, as it is affected by cooler water, it becomes increasingly susceptible to winds coming from any other direction, which act to slowly tear the storm to bits. Thus, a storm traveling directly from the east toward Hawaii stands little chance of surviving its journey across the cool central Pacific.

This was the path attempted by Hurricane Felicia in early August 2009. At one time, Felicia was a monstrous Category 4 hurricane with winds of 145 mph. This prompted landfall concerns as it spun westward toward Hawaii`s Big Island. However, as Felicia crossed the central Pacific, it slowly started to weaken over the cooler water, and then was pulled northward and shredded as it encountered wind shear about 400 miles to the east of Hawaii. By the time the storm approached the Aloha State, it possessed little of its former power.

Hurricane Iselle in 2014 also took an identical path as Felicia, but the one-time Category 4 storm while over the Eastern Pacific was able to maintain some strength, making landfall on Big Island of Hawaii as a tropical storm. This storm did cause at least one death from flooding and almost $80 million in damage.

In 2016, Hurricane Darby moved westward across the eastern and central Pacific, becoming a Category 3 hurricane with winds of 115 mph well east of Hawaii. By the time it crossed the cooler water east of Hawaii, the system was a weak tropical storm at landfall near Pahala on the Big Island. It did produce flash flooding and caused minor damage on the Big Island, Maui and the greater Honolulu area on Oahu.

Hurricane Madeline took a similar path as Darby and Iselle did earlier. It too weakenes as it moves over the cooler waters upon its approach of the Hawaiian Islands. It brought some storm surge flooding and heavy rain to the eastern side of the Big Island of Hawaii.

This is not to say that Hawaii is completely protected from tropical storms. There is one direction in which the Islands are susceptible to a hurricane invasion: from the south.

The pool of warmer water remains intact across the Pacific between 500 and 750 miles south of the Hawaiian Islands, and a hurricane which forms and moves due westward about 600 miles south of Hawaii can maintain its strength into the central Pacific. If winds direct the storm northward toward the Islands, it has a chance to survive.

This path was taken in 1992 by Hurricane Iniki, which moved west across the central Pacific along this route, then made a right-hand turn to the north and sliced a path across Kauai, one of the western islands in the chain. Iniki made landfall as a Category 4 hurricane, packing winds of 140 mph. Its destruction was immense, with nearly 5,000 houses damaged and another 1,400 destroyed.

Image: Hurricane Madeline churns the Pacific east of Hawaii on August 29th. I(NASA Goddard Rapid Response Team)