HURRICANES IN HAWAII Page 1 of 6 HURRIC NES InHa HURRICANES form in areas of enhanced th derstorms over warm, tropical oceans and are the most destructive storms on Earth (Fig r~.J). The destructive fury of hurricanes comes from a combination of high wi ds, heavy rains, and abnormally high waves and storm tides. The deadliest hurricane in U.S. history occurred in Galveston, Texas in 1900 when an estimated 6000 people pe ished. One of the costliest natural disasters ever to hit the U.S. was Hurricane And ew, which resulted in more than $30 billion in losses and 53 related deaths. In the wes m North Pacific, the storms that annually threaten the Philippines and Japan are c lIed typhoons. Over the Indian Ocean the same type of storm is called a cyclone. In 197 more than 300,000 people lost their lives in a storm surge and tide that struck BangIa esh. A storm surge is a rise in the level of the sea caused by effects of wind and low atm spheric pressure on the ocean. Figure 1: High resoluti n infrared image ofI-Iurricane Iniki making landfall 0 Kauai at 3: 15 PM HST on 11 Septenlber 1992. The i age was taken by a NOAA polar orbiting satellite ~500 ile above the Earth. (Click on image to see full ize) Hurricanes in Hawaii: Hurricanes are relativ ly rare events in the Hawaiian Islands. Records show that strong wind storms have struc all major islands in the Hawaiian Island chain since the beginning of history. The fitst officially recognized hurricane in Hawaiian waters was Hurricane Hiki in August f 1950. The identification of tropical cyclones improved with increased commerce and ircraft activity following WWII and improved dramatically with the launch of the TIR: S 1 weather satellite in April of 1960 (Figpr~1). lNlKl 1992 Figure 2: All tropical cyclone tracks passin within ~200 miles of the coast of the Islands ofHa aii during the period 1949 to 1997. Prior to 1950, a general lack of wind data has resulted in a s etchy 20" record. From 1832 to 1949 only 19 tropical _ Htwric"'il'''~ cyclones were identified from scattered wri en __ T~a1am ---T~~IMIIOnOfhM. records and ship reports. - ~200rm.1'IIOgll from ilhndCOD~»' http://www.soest.hawaii.edu/MET/Faculty/businger/poster urricane/ 9/13/2007 HURRICANES IN HAWAIl Page 2 of6 (Click on image to see full size) Since 1950 five hurricanes or tropical storms hav caused serious damage in Hawaii. Hurricane Nina (1957) produced record winds i Honolulu. Hurricane Dot (1959) caused damage to Kauai. Hurricane Estelle (1986) produced very high surf on Hawaii and Maui and floods on Oahu. Kauai also receive the brunt of Hurricane Iwa, which struck on 23 November 1982 and produced an es imated $234 million in damage. The destructive force of hurricanes in Hawaii wa powerfully demonstrated on 11 September 1992 when Hurricane Iniki struck th island ofKauai with sustained winds of 130 mph and caused over $2.3 billion in prope y damage (Figure 3). Figure 3: Sheets of roo ng iron, a pallet, broken plants and other debris fly thr ugh the air at the height of Hurricane Iniki in Lihu ,Kauai (Photo by Bruce Asato, courtesy ofthe Honolul Advertiser). (Click on image to see full ize) Anatomy of a Hurrica e: The core of a hurricane is characterized by a small central region known as e eye, within which the winds are light and there are few clouds. Winds increase rap dly as one moves out of the eye and into a surrounding ring of thunderstorms referred 0 as the eye wall (Figure 4). The winds in a hurricane are a maximum near the surD ce and decrease with height. In the Northern Hemisphere, a hurricane's circulation in ludes low pressure and counter­ clockwise inflow at the surface, and high pressure and clockwise outflow at upper levels (Figure 5). The overall diameter of the hurricane irculation is typically between 300 and 600 miles. Figure 4: Schematic sh I ing path and destructive elements of Hurricane I iki across Kauai. Hurricanes impact Hawaii through e combined effects of strong winds, possible tornado s, torrential rains, and elevated tides and large waves 0 coastal and inland areas. These destructive forces are m gnified on the right side of the eye wall when facing in the direction in which the '----'--~----' hurricane is moving. (Click on image to see full size) Figure 5 Conceptual diagram showing the http://www.soest.hawaii.edu/METIFacultyIbusinger/poster urricanel 9/1312007 HURRICANES IN HAWAII Page 3 of6 interna structure and circulation of a mature hurricane. (From NOAA, Hurrican , Washington, DC: Superintendent of Documents, 1977) Given a source of mo sture from a warm ocean surface and a lack of destructive wind shear, hurric nes typically last for a week to 10 days. (Click on image to see full size) Hurricane Formation: The necessary condit" ns for one of the numerous convective disturbances over the tropical oceans to intensify nto a hurricane are related to the wind field's ability to produce and concentrate warm ai . Warm air is less dense than cold air leading to low surface pressure. As the wind stre th increases over a warm ocean surface, the flux of heat and moisture also increas s and a cycle of intensification results. Only one in ten tropical disturbances (winds up to 38 mph) develops into a tropical storm (winds 39 to 74 mph), but fully seven in ten tropi al storms do develop into hurricanes (winds >74 mph). Together these storms are refe ed to as tropical cyclones. There are five prerequisites for hurricane for ation that are related to the formation of the warm core in the hurricane. (p Warm ocean water with temperature more than 80°F (26°C) to a depth of ~100 feet (59 m), so that cooler water cannot easily be mixed to the surface by winds. (2) Unstable atqlOsphere characterized by enhanced thunderstorm activity. Latent heat is released effic~ently in the updrafts of deep clouds. (3) High relative humidity in the middle troposph~re; moist air weighs less than dry air, making it buoyant and contributing to lower surfa~e pressure. (4) A pre-existing disturbance with cyclonic circulation; as the air in the disturbance converges, angular momentum is conserved and the wind speed incre ses. (5) Small wind shear or little change in the wind speed or direction with height n the vicinity of the developing storm so that warm air is concentrated over one area and not blown apart by the winds. When a hurricane moves over land or cold water, the supp y of energy is reduced, and the wind speeds diminish. Over land, frictional forces also ct to weaken the storm. Figure 6: Tracks of all Central Pacific ~_ ) hurric nes from 1949 to 1997. Track segme ts for hurricanes of category 3 are shown in red. August mean positions of areas f warm (>83°F) and cool ocean water 180°F is minimum SST for hurricane forma 'on) are indicated by shading. Augus I mean wind conditions at the surfac are indicated by arrows and the -"=-----;'::".~i""'" 1016 b contour of constant sea-level pressure (isobar). August mean wind condition aloft are indicated by the 200 mb ridge line that separates easterly from westerly ow aloft (arrows). Most of these storms (-70°Jlo) form over the eastern Pacific an pass into the central Pacific from http://www.soest.hawaii.edu/MET/Faculty/businger/poster urricane/ 9/13/2007 HURRICANES IN HAWAII Page 4 of6 the east. The mean storm track follows paralle to the summer mean sea-level pressure contours (isobar) and stays over war water. (Click on image to see full size) The climatology of hurricane tracks over the cent al Pacific shows a mean track passing to the south of the Hawaiian Islands (Figure 6) a d a maximum hurricane occurrence during the late summer when the ocean surface is warmest (Figure 7). Storms that approach the Hawaiian Islands from due east hav historically weakened east of Hawaii under the combined influence of unfavorable wes erly wind conditions aloft, resulting in large wind shear and cooler sea-surface temperat res. However, natural variability in the circulation of the ocean and atmosphere has allo ed potentially destructive depressions and tropical storms to reach Hawaii from the east ince 1950 (Figynt2), and there is historical evidence of one early hurricane (1871) at approached from the east and impacted the islands of Hawaii and Maui. Hurric es Dot, Iwa, and Iniki all approached from the south and passed near Kauai. This unusu I track requires a breakdown of the semi-permanent ridge of high pressure to the nort of the islands, which occurs when a trough of low pressure in the midlatitude westerli s approaches the island chain from the northwest. Such troughs are generally confined to higher latitudes, except in winter. ~o Central PacH'i~' Hurricane OCcurrence I .., i Figure 7: Monthly climatology of hurricane occurrence in ::,~=7C",ogo'Y3 I the Central Pacific. The peak in hurricane a tivity is in late § f' summer when ocean temperatures are war est. ?i (Click on the image to see full size) Figure 8 Destr ction in the wake of Hurricane Iniki. (Photo b Charles Fletcher). (Click on the im ge to see full size) Hurricane 1m act in Hawaii: The potential for property damage in Hawaii is increased because of the numerous lightly constructed buildings and dwelli gs (Figure 8). Flying debris from these structures and airborne vegetation increase t e potential for serious damage to neighboring properties and utility lines Cf]gyre3).