hurricane Iniki Hawaiian Islands Dr. George Pararas Carayannis

Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions, Climate Change and other Natural and Man-Made Hazards and Disasters - Disaster Archaeology,

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Hurricane Iniki of September 5 - 13, 1992 in the Hawaiian Islands

Examination of its Anomalous Path

George Pararas-Carayannis

(©) Copyright 2007 George Pararas-Carayannis

INTRODUCTION

The last hurricane to strike the Hawaiian Islands was Iniki in 1992. Iniki was a small but intense hurricane (minimal category Four) which made landfall on Kauai where it killed six people and caused $2.5 billion in damage. Until the 2005 Hurricane Katrina, Iniki was the thrd most destructive hurricane in U. S. history and the most destructive to hit the Hawaiian Islands in the 20th Century.

On the average , the Hawaiian Islands region gets an average of 4.5 tropical storms per year and one hurricane approximately every 15 years. Most of the tropical depressions in this central region of the Pacific, usually pass south of the Island of Hawaii amd bring heavy rains but do not cause major problems to the Islands. However, Iniki was an exception and an anomaly that could very well occur again in the future. What was unusual about Iniki was the sudden change of its track path in a northward direction in the morning hours of September 10, 1992 and its intensity when it made landfall on Kauai. A detailed description of Iniki's winds and surge flooding effects in Kauai were provided previously in another report (http://www.drgeorgepc.com/HurricaneIniki.html ). The present report examines the 1992 high hurricane and storm activity in the Eastern Pacific Region and the causes that steered Iniki northward to strike Kauai. Another report provides an overall risk assessment of hurricanes in the Hawaiian Islands and presents a scenario of the potential impact that a hurricane, similar to Iniki, would have if it made landfall on the southern coast of Oahu, or passed in closer proximity to a metropolitan area such as Honolulu.

Iniki's Formation: As illustrated in the diagram below, 1992 - an El Nino year - was prolific for hurricanes and storms in the Eastern and Central Pacific.

Tracks of Storm Systems and Hurricanes in the Eastern Pacific in1992, including Hurricane Iniki

Iniki formed as a tropical depression near 12 N 135 W on September 5, 1992, about 1600 statute miles southwest of Baja California - crossing 140 W into the Central Pacific on the morning of September 6.

As the depression moved westward, it began to intensify and was upgraded to a tropical storm on the 8th of September. Iniki was further upgraded from a tropical storm to a hurricane when it was near 13 N, 152 W, or about 470 miles SSE of Hilo.

Hurricane Iniki continued to strengthen while on a west-northwest course - passing 300 miles south of South Point of the Island of Hawaii. When it was located near 14 N 156 W, or about 385 miles SSW of Hilo, its maximum sustained winds had reached 85 knots. Iniki continued in a west-northwest direction at a speed of translation ranging between 12 and 15 knots on September 9, and was near 15 N 158 W, or about 425 miles south of Honolulu. During the morning hours of September 10, at about 5 am HST Iniki was near 15 N 159 W or about 410 miles south of Honolulu. At that time Iniki began to slow its forward motion speed but continued moving in a generally west-northwest direction at about 10 knots. At the time, maximum winds had reached 100 knots and the central pressure was 951 millibars. Then Iniki slowed even more and started to turn in a northwest direction. When its center was near 15 N 160 W, or about 400 miles south of Lihue, Kauai, the storm system had strengthened with maximum winds estimated at 110 knots and gusts up to 135 knots. Then suddenly, Iniki changed completely direction and begun to move northward towards the island of Kauai.

 

Watches and Warnings for Iniki: Based on these changes a hurricane watch was issued for the western Hawaiian chain from Kauai and Niihau, west to French Frigate Shoals on September 10, 1992. On the morning of September 11, hurricane warnings were issued for Kauai and Niihau and tropical storm warnings were issued for Oahu. A tropical storm watch was issued for the Islands of Maui, Lanai and Molokai. High Surf Advisories were continued for all of the Hawaiian chain.

Track of Hurricane Iniki, in 5-13 September 1992.

Iniki's Track Before Landfall on Kauai: Iniki continued to turn more northward while accelerating. Iniki was well-tracked and average wind velocities and maximum winds were fairly well estimated or measured by aerial reconnaissance dropsondes during its fully developed phase on the 10th and 11th September 1992.


Iniki continued to strengthen during the early morning hours of September 11 as it moved north along 160W. At 0900Z, on September 11, Iniki was located near 17.5 N 160 W or 310 miles south of Lihue and continued to move north with a speed of translation of 12 knots. Hurricane warnings were extended eastward to include the island of Oahu. By 2100Z, of September 11th, Iniki was near 20 N 160 W , or about 130 miles south southwest of Lihue> It continued to move north or a bit east of north but its speed of translation had increased to 15 knots. Maximum sustained winds had increased and were estimated at 125 knots with gusts as high as 150 knots. The central pressure was measured to be 938 millibars - the lowest pressure ever recorded in a Central Pacific hurricane up to that time.

Iniki's Landfall and Departure: Iniki moved faster north, rapidly approaching the southern Kauai coast. At 12/0100Z its center was located near 21.6 N 159.7 W or 37 miles southwest of Lihue. The central pressure was 945 millibars and maximum winds were about 127 knots. In the afternoon of September 11, at 3:30 pm HST, the eye of Iniki crossed Kauai's south coast, just west of Port Allen near Kaumakani, just east of Waimea. When Iniki moved over Kauai, its central pressure was approximately 945 millibars, and the estimated maximum sustained winds over land were 145 mph, with gusts up to 175 mph miles - making Iniki the most powerful hurricane to strike the Hawaiian Islands in recent history. Iniki moved on a bearing of about 15 degrees on the compass across Kauai while accelerating to 25 knots. Fortunately, Iniki moved fast over Kauai and departed Haena on the north coast about 40 minutes after landfall. Subsequently, it continued north and, at 12/0300Z, was centered 50 miles north of Kauai's Na Pali coast. By that time Kauai was in ruins.

Satellite image of Hurricane Iniki on September 11, 1992 at 2358 UTC (NOAA Image)


The hurricane warning for Oahu was subsequently downgraded to a tropical storm warning. The tropical Storm Warning for Oahu and Maui County was canceled at 12/0600Z when Iniki was 120 miles north of Kauai moving north , now at 25 knots and weakening, with top winds down to 100 knots. The hurricane warning for Kauai was downgraded to a tropical storm watch at 12/0900Z. The watch was then cancelled at 12/1200Z.

 

The eye of the Iniki crossed the Kauai Coast just west of Port Allen near Kaumakani just before 4 PM Hawaiian Standard Time (HST). The most severe damage in Kauai occurred on the south, east and north of the island.

Iniki continued to move north and to weaken. At 12/2100Z, it was located 500 miles north of Kauai, near 29 N 159 W, with maximum winds now down to about 80 knots. It decreased to tropical storm strength by 13/1500Z near 36 N 158 W and was considered extratropical as it continued to move north, while entangling itself with an approaching low pressure system and a cold front.

Winds on Oahu: The most severe conditions from Iniki - measured at Wheeler Air Force Base on 11 September 1992 - were winds of 29 knots from the Southeast, gusting to 47 knots. The wind directions changed from 275 to 104 degrees. At Barber's Point the winds were from the Southeast at 34 knots gusting to 45 knots.

Storm Surges on Kauai: Iniki was accompanied by storm tides ranging from 4.5 to 6.3 feet above normal, with 20 to 35 foot storm waves superimposed. Heavy waves battered the coastal areas of southern Kauai. Highest values occurred at Port Allen and Poipu. Maximum flooding begun around 3:30, as indicated by the Port Allen tide gauge, prior to the passage of the hurricane's eye nearby. At that time the astronomical tide was the highest and it was augmented by the reduction of the barometric pressure as the hurricane moved over the island. Superimposed on the higher elevation of the hurricane surge were the storm waves, which intensified around that time, as the winds were maximum and the landward component of wind friction also reached maximum value.

 

Aerial photo of debris line (innermost white line) at Poipu Beach, Kauai, illustrating the degree of Iniki's hurricane storm surge flooding.

The highest water levels and inundation of up to 22 feet above mean lower low water (MLLW) were reported by the Army Corps of Engineers near the Poipu area of Kauai. However, flooding of up to 27 feet above MLLW was reported by the Civil Defense. A University of Hawaii survey claimed maximum inundation of 29 feet above MLLW.

Storm Suges on Oahu: On Oahu, Iniki produced tides of 1.7-3 feet (0.5-0.9 m) above normal. Superimposed on the elevated height of the sea were the storm waves. Prolonged periods of high waves severely eroded and damaged the southwestern coast of Oahu, with the areas most affected being Barbers Point through Kaena Point. The Waianae coastline experienced the most damage, with waves and storm surge flooding the second floor of beachside apartments. In all, hurricane Iniki caused several million dollars in property damage, and 2 deaths on Oahu.

Water Level Measuring Stations: On Kauai, the NOS tide station at Port Allen was the only continuous recording of water level as affected by hurricane Iniki. On Oahu a continuous recording of water level was made by the NOS tide station at the Coast Guard pier in Honolulu Harbor. These stations also recorded the barometric pressure fluctuations. Deep water buoy 51002, anchored some 280 miles south southeast of Honolulu, had recorded significant wave heights of about 20 feet, which would indicate a most probable wave height of about 36 feet, which was consistent with what was observed along the south shore of Kauai.

Wind Reporting Stations: There is no much wind data collected for hurricanes occurring in the vicinity of the Hawaiian Islands because most of the recording stations are on land and separated by great distances. The only deep ocean buoy (510020) - close enough to record wind and wave data for Iniki - is anchored about 280 miles south southeast of Honolulu. On the island of Kauai, only WSO Lihue, the Navy station at Barking Sands, and stations at Makahuena, Princeville, Makaha Ridge, and Port Allen provided some wind data - some of the time. There is not a great deal of wind data for the southern part of the island of Kauai and very little data for Oahu. The only stations that reported briefly wind data from Kauai were Port Allen and Makahuena (until it lost power).

Iniki's Damage and Destruction: The most severe damage occurred on the south, east and north of Kauai. Surge damage was heaviest along the south shore of Kauai and affected shoreline hotels and condominiums, especially around Poipu. Extensive wind damage begun in the Poipu area as early as 1:15 to 1:30 in the early afternoon of September 11. Wind damage was extremely heavy throughout Kauai as many homes and buildings were flattened or lost their roofs. The number of homes that were completely destroyed was 1,421. A total of 63 homes were destroyed by wave action or storm surges on the south coast of the island. The number suffering major damage was 5,152 while 7,178 received minor damage. Electric power and telephone service were lost throughout the island and only 20 percent of power had been restored four weeks after the storm. Crop damage was likewise extensive as sugar cane was stripped or severely set back, while tropical plants, such as banana and papaya, were destroyed and fruit and nut trees were broken or uprooted. The overall monetary value of the damage caused by Iniki in the Hawaiian Islands reached close to 3 billion dollars.


Some damage also occurred on the islands of Maui County and the Big Island of Hawaii, where swells and heavy surf from southwesterly directions pounded exposed shorelines and anchorages.


On Oahu, the areas most affected were the leeward coast from Barbers Point through Makaha and Kaena Point, with lesser damage along the south shore from Ewa Beach to Hawaii Kai.

Iniki's Anomalous Path: In the early morning hours of September 10, 1992, Iniki was located near 15 N 159 W, or 410 miles south of Honolulu, but still moving in a generally west direction at 10 knots. It looked as though it would miss the islands. However, subsequent unpredictable flow changes in the overall Central Pacific circulation changed Iniki's path to a northward direction. What deflected Iniki's path in a northward direction was the fact that the western edge of the subtropical high-pressure ridge, a semi permanent feature found north of Hawaii, had weakened. Normally, this pressure ridge keeps hurricanes south of the islands. However, in September 1992, a weakness in this ridge had developed west of 160 W when a large low system or trough began to drift south along and just east of the International Dateline at 180 W. This air mass flow change caused Iniki to change its path in the early hours of September 10 and head north of its previous west-northwest track - bringing it closer to the islands.


Other 1992 Hurricanes and Storm Systems in the vicinity of the Hawaiian Islands after Iniki

In the days and weeks following Iniki, the Hawaiian Islands were affected by four additional storm systems.

Hurricane Roslyn - September 24 - 30, 1992: Hurricane Roslyn moved into the Central North Pacific area early on September 24, crossing at 140 W near 18 N with winds estimated at 75 knots. Roslyn weakened as it moved slowly westward along 18 N and was downgraded to a tropical storm 24 hours later near 145 W. On the 27th, near 18N 150W, shearing aloft occurred and the weakened system began to move northeast and later north over the waters northeast of the Hawaiian Islands where it dissipated. The only effect the weakening cyclone had on the Hawaiian Islands was some higher than normal surf along its eastern shores.

Tropical Depression Tina - October 9 - 11, 1992: Tropical Depression "Tina" crossed into the central North Pacific on October 9 near 24 N 140 W. "Tina" dissipated as it moved in a northerly direction just west of the 140th west meridian. "Tina" had an unusually long life span, which lasted nearly 3 weeks. Tina had no significant effect in the Hawaiian Islands.

Tropical Depression Yolanda - October 22 - 23, 1992: Tropical Depression "Yolanda was dissipating by the time it entered the Central Pacific. It had been sheared and completely stripped of its deep convection as it reached near 16N 140W moving west at about 12 km. An advisory was issued early on October 22 on the dissipating system. The following day the remnant circulation passed to the south of the Big Island of Hawaii, bringing a few showers to its windward coast.

Tropical Depression Three-C - November 21 - 22, 1992: High sea surface temperatures persisted in the equatorial areas of the Central Pacific even though the 1991-92 El Nino had officially ended. As a result, widespread cloudiness and showers persisted to the south and west of the Hawaiian Islands. A small disturbance did form within a cloud mass centered near 10 N 150 W. The disturbance tracked west and developed a closed circulation near 11 N 155 W and was subsequently named Tropical Depression THREE-C late on November 21. TD3C never developed past the depression stage and the last advisory was issued about 24 hours later, when the system was dissipating near 10 N 157 W.

REFERENCES AND ADDITIONAL READING


Brown R. H. (1993).
Natural Disaster Survey Report: Hurricane Iniki. URL accessed on 2006-03-13.

Central Pacific Hurricane Center (1992). The 1992 Central Pacific Tropical Cyclone Season. URL accessed on 2006-03-13.

National Hurricane Center (2004). Costliest U.S. Hurricanes 1900-2004 (adjusted). URL accessed on 2006-03-18.

Pararas-Carayannis G. Hurricane Surge Prediction - Understanding the Destructive Flooding Associated with Hurricanes http://drgeorgepc.com/HurricaneSurge.html

Pararas-Carayannis G. HURRICANE INIKI IN THE HAWAIIAN ISLANDS September 11, 1992

http://drgeorgepc.com/HurricaneIniki.html


Pararas-Carayannis, G., 1975.
"Verification Study of a Bathystrophic Storm Surge Model". U.S. Army, Corps of Engineers - Coastal Engineering Research Center, Washington, D.C., Technical Memorandum No. 50, May 1975 (Study performed for the U.S. Nuclear Regulatory Commission for the licencing of the Crystal River (Florida) nuclear plant).


Pararas-Carayannis, G.,1993.
The Wind and Water Effects from Hurricane Iniki on September 11, 1992, at Lawai Beach Resort, Poipu, Island of Kauai, Hawaiian Islands. A study prepared for Metropolitan Mortgage & Securities Co., Inc, Spokane, Washington,and the Ritter Group of Companies, Chicago, June, 1993.

US Army Corps of Engineers (1993). Hurricane Iniki Assessment. US Military. URL accessed on 2006-03-13.

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