Kwajalein Info

EM Home Be Informed Make a Plan Build a Kit Mass Notification

Geographical Data:

Location: Kwajalein Atoll is located in the “Ralik” (sunset or western) chain of the Marshall Islands in the West Central Pacific Ocean. It is 2,100 nautical miles southwest of Honolulu and about 4,200 nautical miles southwest of San Francisco. Lying less than 700 miles north of the equator, Kwajalein is in the latitude of Panama and the southern Philippines. It is in the longitude of New Zealand, 2,300 miles south and the Kamchatka Peninsula of the former Soviet Union, 2,600 miles north. Its remoteness from centers of population and its proximity to the sea has a major bearing on the operation and maintenance of USAG-KA/RTS.

Atoll Configuration and Size: Kwajalein Atoll is a coral reef formation in the shape of a crescent loop enclosing a lagoon. Situated on the reef are approximately 100 small islands with a total land area of only 5.6 square miles (3,854 acres). The largest islands are Kwajalein (1.2 square miles), Roi-Namur and Ebadon at the extremities of the atoll. Together they account for nearly half the total land area. While the “typical” size of the remaining islands may be about 150 yards X 700 yards, the smallest islands are no more than sand cays that merely break the water’s surface at high tide. In contrast, the lagoon enclosed by the reef is the world’s largest, having a surface area of 1,100 square miles. Its depth is generally between 20 to 30 fathoms (120 to 180 feet). However, there are numerous coral heads approaching or breaking the lagoon surface. The atoll’s longest dimension is 75 miles from Kwajalein to Ebadon and its average width is about 15 miles. Kwajalein, at the atoll’s southern tip and Roi-Namur at its northern

extremity, are the principal islands at USAG-KA/RTS.

Atoll Structure: Coral atolls are seamounts, which are capped by calcareous marine growth constructed by lime-secreting organisms (coral polyps and algae). Presumably, the lower parts are composed of non-calcareous rocks, usually volcanic materials. The coral superstructures may be hundreds or even thousands of feet in thickness. Emergent portions of reef and islands are composed of loose, poorly consolidated calcareous materials derived from foraminifera, coral, shells and marine algae or their debris, resulting from destructive action of the elements. One notable characteristic of atolls is the steep slopes of the mountain seaward of the reef. Around Kwajalein Atoll, the depth plunges to as much as 1,000 fathoms (6,000 feet) within two miles of the atoll and 2,200 fathoms (13,200 feet) within 10 miles. The Kwajalein Atoll reef lies at intertidal level, mostly exposed at low tide and submerged at high tide. There are about 25 passages from the open ocean into the lagoon, through or over the reef, which will admit small boats. Ocean going ships ordinarily use Gea Pass, 10 miles north-northwest of Kwajalein.

Elevation: All islands of the atoll are quite flat with few natural points exceeding 15 feet above mean sea level. The average elevation of Kwajalein is 5.9 feet. Its highest point, “Mount Olympus,” the original missile launch hill, is about 57.6 feet high and is man-made. Because of the coral base and the lack of elevation of the islands, there is a very shallow water table. This

condition presents a major problem for underground construction.

Climate and Weather

Kwajalein has a tropical marine climate characterized by a relatively high average annual rainfall of nearly 100 inches and warm-to-hot, humid, weather throughout the year. The principal rainfall season extends from May through mid-December, with about 75 percent of the annual rainfall recorded during this period. A pronounced diurnal cycle exists in the tropics, with two thirds of atoll rainfall typically recorded between midnight and sunrise. Easterly winds, almost constant cloudiness, and frequent moderate to heavy showers prevail during the wet season. The dry season weather is routinely considered to be from mid-December through April with lighter showers of short duration, but not a complete absence of significant rainfall events. In this “dry” season, brisk trade winds out of the northeast are persistent and cloudiness is at a minimum.

Local Climate Variations: Periodic warming of equatorial waters (El Nino) greatly alters wind, wave, and weather patterns, which not only affects weather on a global scale but can have great effects in the Marshall Islands. For Kwajalein Atoll, El Nino can trigger more extreme local conditions, for example, more frequent tropical cyclones. Similarly, abnormal cooling of equatorial waters (La Nina) also disrupts weather patterns, but along generally less predictable patterns. These events are called El Nino-Southern Oscillation (ENSO) events.

Temperature: Temperatures vary little from day to day and month to month. Typical daily average temperatures are a low of near 78 degrees Fahrenheit (F) and a high near 87 degrees F. Due to the low latitude, only slight variations occur in the length of daylight and the altitude of the sun. The small variation in solar energy and moderating ocean influence are primary reasons for such uniform temperatures in the area. The average monthly temperature is 82.2 degrees F. Normal temperature range between the coldest and warmest months is about one degree F, with an average daily temperature range of 10 degrees F. Maximum daily temperatures occur in the early afternoon and the minimum occurs during showers or in the early morning. The highest temperature ever recorded was 97 degrees F while lowest was 68 degrees F.

Relative Humidity: The relative humidity is quite high, with the 30-year normal being 79%. Relative humidity is typically 70% to 80% during the day and 80% to 90% at night. Humidity is on the low end of the range in the dry season and the high end in the wet season. Unusually dry episodes occur a few times in each dry season, when the humidity drops below 70%.

Winds: Northeasterly trade winds are dominant most of the year. From December through June, the wind blows mostly from the east-northeast (the bearing of the Kwajalein aircraft runway) at speeds averaging about 17 miles per hour. During the summer months, winds are generally weaker with occasional doldrums of almost no winds; the direction tends to be more easterly, sometimes southeasterly, and even westerly on occasion. Winds seldom exceed moderate gale strength (38 miles per hour). Typhoons are rare in the immediate vicinity of Kwajalein but are possible at any time of the year due to the warm water temperatures in the region. Significant west-wind and west-swell episodes have been recorded and appear particularly associated with strong El Nino events. West winds can also occur in the atoll with transiting tropical cyclone threats. Many Kwajalein Atoll harbors lack protection from west-winds and the swells produced by a lengthy period of these winds.

Clouds: Partly to mostly cloudy skies, with one-half to three quarters cloud cover, prevail most of the time. Periods of scattered to broken cumulus clouds (40-90% sky coverage) with bases at 1,500 to 2,000 feet are common throughout the entire year. The atoll does not experience fog and only heavy showers reduce visibility below two miles.

Dry Season and Droughts: The dry season is of particular significance to an installation such as USAG-KA/RTS. As many as 19 weeks have passed with practically no rainfall (in 1983 the rainfall for January-May was only 3.89 inches). Light showers of short duration fall on dry, heated ground and render little, if any, catchable water. During the dry season, fresh water consumption exceeds the amount of rainfall available from catchments and it is necessary to obtain fresh water from lens wells or from seawater treatment.

Kwajalein had severe dry seasons in 1983 and 1984, with 1984 being the driest year on record. Kwajalein sustained a severe dry season in the first half of 1992. Other phenomena can affect the water supply and worsen a drought. For example, Tropical Storm Zelda (November 1991) decreased the fresh water available on many atolls from salt water intrusion in the fresh water wells. The U.S. government provided aid in supplying fresh water from Kwajalein to several outer islands and atolls. In 1995, permanent seawater desalinization capabilities were installed to augment fresh water reserves. Drought conditions attributed to ENSO event followed Typhoon Paka in December 1997 and in 2016 after the 2015 ENSO events.

Rainfall and Heavy Rains: Average annual rainfall at Kwajalein is slightly less than 100 inches. Variation can be significant and ranges from a low of 59.35 inches in 1984 to a high of 149.13 inches in 1950. Heavy rainfall rates are greater than 0.30 inch per hour or more than 0.03 inch in six minutes.

These events can happen in any month of the year, though more common in the wet season than the drier period. Pooling or ponding of water occurs on hard surfaces and in low lying areas of yards or grass covered areas. Reduced visibility can be less than one-quarter mile.

Lightning: Strong convection is common around Kwajalein and produces lightning. Statistics for lightning occurrence cannot be rigorously evaluated over the atoll due to repeated power outages at the outer islands with sensors (decreases in count), communication link issues causing timing issues for location (decreases in count), and radar interference (false additions to the count generally north of the atoll). Therefore, total counts over this large atoll are not accurate due to the difficulty in observations and the remoteness of the area. But the data provides insights into lightning activity in the area by observing the general strike frequency, which was not being recorded before the establishment of the local lightning system. The data also provides an insight into the differences of lightning occurrences between warm (higher activity) and cold (lower activity) water regimes, with the deep convection producing the lightning events. Our most current lightning study (April 2014) shows an occurrence of lightning over and within the atoll of 0.15 flashes per square kilometer per year. For a lagoon size of 1700 square kilometers, this represents an average of 255 strikes over the atoll per year. But, yearly averaging does not reconcile the local risks or differences associated with warm and cold water situations. Establishing solar powered systems and improved communications are producing more accurate counts and these improvements are now coming on-line; the general evidence is that there is

much more lightning than documented by human observations that were the basis for erroneous conclusions from the past data.

Tsunamis: Kwajalein has a low risk for devastating effects from tsunamis. For a tsunami to produce devastating inundation and damage along coastlines, the sea floor must gradually rise up to the shoreline. This forces the tsunami to slow down and build in height, producing a high amplitude wave that can wash inland and cause significant damage. In contrast, Kwajalein Atoll, along with the other atolls of the Marshall Islands, has an extremely steep drop-off from the reef front into deep ocean waters. This prevents a tsunami from building up and allows them to predominantly pass with little noticeable effect.

However, tsunamis can have an effect on Kwajalein if certain conditions exist. If a powerful tsunami moves through the area at or near high tide, it can move enough water over the Oceanside reef to cause some inundation. In addition, parts of the atoll have large ocean-side reef areas that are shallowly submerged. Should a tsunami come from a direction that allows it to directly impact such a reef area, then some inundation is likely to occur. This occurred during the Tohoku earthquake and tsunami on 11 March 2011, with a 9.0-9.1 magnitude. With the tsunami propagating from the northwest, Roi-Namur and other areas along the northern atoll experienced more inundation from the wave crests than areas further south due to protection of the northern atoll. Island Security reported that boats at the Small Boat Marina hit the bottom as the surge receded inside the lagoon, while there were other reports of damage to the northern shoreline and breakwaters with minor flooding or splash over in some areas.

Tropical Cyclone Threats: The generic term for Tropical Disturbances, Tropical Storms (TS) and Typhoons (TY) is tropical cyclone. Typhoons are classified as tropical cyclones with sustained winds greater than or equal to 64 knots (74 mph), while tropical storms contains winds between 35-63 knots and tropical depressions contain winds between 25-35 knots. Due to Kwajalein’s location, typhoons are rare. Tropical storms and tropical depressions, which are less intense than typhoons, are more frequent.

History of Tropical Cyclones at USAG-KA

In January 1988, TS Roy caused extensive shoreline damage at Kwajalein. Various facilities were damaged, mostly the roofs, with the damage estimated at approximately two million dollars for Kwajalein. Because of the storm’s track, most of the damage was to buildings on the ocean side and the shoreline areas along the runway and golf course. Ebeye received even worse damage, leaving 3,500 people homeless, with major damage to more than 50% of the homes, while 30% were destroyed.

TS Zelda came through Kwajalein on Thanksgiving Day 1991 with 55 knot sustained winds and peak gusts of 71 knots. Zelda’s winds and driving rains uprooted trees and severely damaged many facilities. The center of the storm passed within 19 miles southwest of Kwajalein. The Federal Emergency Management Agency (FEMA) declared Kwajalein Atoll a disaster area with damage totaling more than eight million dollars.

TY Paka passed 83 miles south of Kwajalein on December 12, 1997. Sustained winds of 39 knots were recorded on Kwajalein, with gusts to 47 knots. While damage was widespread, it was generally minor.

In December 2004, TS Talas made its way through the Marshall Islands, affecting Kwajalein Atoll from the evening hours of December 10 through the morning hours of December 11. Talas’ track brought it 16 miles south of Kwajalein. The weather station recorded sustained winds of 40 knots, with gusts to 56 knots. There were a few structures on Kwajalein that sustained significant structural damage; however, the storm’s overall impact was not great. Reports indicated more severe damage on Ebeye, with many roofs blown off and significant structural damage to houses.

TS Bavi formed in the RMI in March 2015 and moved within 111 miles southwest of Kwajalein. The Kwajalein Atoll experienced several days of blustery winds in excess of 25 knots with several short peaks of sustained winds over 34 knots. The maximum sustained wind speed was 36 knots with a maximum-recorded gust of 44 knots. TS Bavi damaged the roofs on several buildings, toppled trees, and did damage at both Roi-Namur and Kwajalein. Damage was estimated to be more than a million dollars.

During strong warm water events (El Nino), the general region for tropical cyclone formation shifts eastward, increasing the likelihood of tropical cyclone activity throughout the Marshall Islands. This can have other effects as well. For example, a disturbance forming west of Kwajalein may cause a period of west winds. The lagoon geography allows westerly winds to pile up water on the lagoon shores of Kwajalein and Roi-Namur Islands, resulting in unusually high surf and wash-over in low-lying areas. Structures such as docks, boats and housing, which are usually sheltered from easterly trade winds, become vulnerable to damage during these conditions. In 2008 and again in 2015, harbor docks and boats were significantly damaged by lagoon waves during west wind swell episode. In addition, rough seas along the watercraft traffic channels in the lagoon hinder transport capabilities, disrupt logistics, and limit safe commutes of the Marshallese workforce.

For more information on how to be prepared for an emergency, please visit the Army Ready and FEMA Ready websites.